Fused filament fabrication (FFF) is a promising additive manufacturing (AM) technology due to its ability to build thermoplastics parts with advantages in the design and optimization of models with complex geometries, great design flexibility, recyclability and low material waste. This technique has been extensively used for the manufacturing of conceptual prototypes rather than functional components due to the limited mechanical properties of pure thermoplastics parts. In order to improve the mechanical performance of 3D printed parts based on polymeric materials, reinforcements including nanoparticles, short or continuous fibers and other additives have been adopted. The addition of graphene nanoplatelets (GNPs) to plastic and polymers is currently under investigation as a promising method to improve their working conditions due to the good mechanical, electrical and thermal performance exhibited by graphene. Although research shows particularly promising improvement in thermal and electrical conductivities of graphene-based nanocomposites, the aim of this study is to evaluate the effect of graphene nanoplatelet reinforcement on the mechanical properties, dimensional accuracy and surface texture of 3D printed polylactic acid (PLA) structures manufactured by a desktop 3D printer. The effect of build orientation was also analyzed. Scanning Electron Microscope (SEM) images of failure samples were evaluated to determine the effects of process parameters on failure modes. It was observed that PLA-Graphene composite samples showed, in general terms, the best performance in terms of tensile and flexural stress, particularly in the case of upright orientation . In addition, PLA-Graphene composite samples showed the highest interlaminar shear strength (about 1.2 times higher than PLA and PLA 3D850 samples). However, the addition of GNPs tended to reduce the impact strength of the PLA-Graphene composite samples (PLA and PLA 3D850 samples exhibited an impact strength about 1.2–1.3 times higher than PLA-Graphene composites). Furthermore, the addition of graphene nanoplatelets did not affect, in general terms, the dimensional accuracy of the PLA-Graphene composite specimens. In addition, PLA-Graphene composite samples showed, in overall terms, the best performance in terms of surface texture, particularly when parts were printed in flat and on-edge orientations. The promising results in the present study prove the feasibility of 3D printed PLA-graphene composites for potential use in different applications such as biomedical engineering. Additive manufacturing (AM) is one of the most promising areas in the manufacturing of components from prototypes to functional structures with complex geometries and is revolutionizing different important industrial areas such as in aerospace, automotive, semiconductor or biomedical applications ,6,7,8,9.The interest in FFF abilities has expanded to include functional finished parts in addition to rapid prototyping. Moreover, the cost of manufacturing small series or unique parts can be significantly reduced . This ha3D printing of polymer composites with enhanced mechanical properties solves the previous limitations by combining the matrix and reinforcements to achieve a system with more useful structural or functional properties non-attainable by any of the constituent alone ,30. IncoThe allure of the recent introduction of nanotechnology into this innovative field is due to the remarkable improvements and diversifications in properties of the resulting 3D printed materials, exhibiting optimized properties and multifunctionality. In particular, there is increasing interest in the development of high-performance composites suitable for 3D printing, achieved via the introduction of nanomaterials with unique properties such as nanotubes and graphene and its derivatives in the polymer matrix. Graphene’s excellent mechanical, electrical and thermal properties make it an attractive candidate for the reinforcement of several polymers . GraphenIn this study, commercially available polylactic acid (PLA), an enhanced PLA-based polymer (PLA 3D850) and graphene nanoplatelet reinforced PLA composite (PLA-Graphene) filaments were used to manufacture different samples by the FFF technique using a low-cost desktop 3D printer. The mechanical properties, in terms of tensile and three-point bending performance, are evaluated. In addition, the interlaminar bonding and impact performance of the 3D printed samples are also studied. The effect of the graphene reinforcement and build orientation are analyzed. A comparison of the mechanical performance, dimensional accuracy and surface texture between virgin PLA and reinforced PLA samples is also conducted. Finally, SEM images of failure samples are evaluated to determine the effects of the process parameters on failure modes.The rest of the paper is organized as follows. First, the experimental methodology carried out in this study is briefly summarized with particular emphasis on specimen preparation, the 3D printing process and the experimental set-up. Thereafter, the key results of the investigation are summarized, and the effects of the different process parameters on the mechanical performance, dimensional accuracy and texture are highlighted. Finally, conclusions and extensions of this work are outlined.® PLA natural [® PLA 3D850 natural [® PLA (PLA-graphene) manufactured by Haydale Ltd.  [® functionalized graphene nanoplatelets (GNPs) of a planar size between 0.3–5 μm in order to improve dispersion and bonding within the PLA polymer. It is expected to improve thermal stability, print quality, the first layer and z-axis adhesion. The goal of this study is to analyze the mechanical performance, dimensional accuracy and texture of PLA-graphene composite samples. Three different commercially available PLA-based filaments, with a diameter of 1.75 mm, have been analyzed: SMARTFIL natural , a modif natural , both fiire, UK) . PLA 3D8The basic mechanical properties of PLA-based materials used in this work and typical ranges of mechanical properties for PLA and ABS materials manufactured by FFF technology provided by the manufacturers are presented in PLA-based samples were manufactured using a WitBox desktop 3D printer developed by BQ . WitBox There are no standard test methods for the mechanical characterization of parts manufactured using FFF. In this study, the recommendations of the ASTM standards D638 , D790 5, D6110-1The mechanical, dimensional and surface finish properties of parts fabricated using FFF technology depend on the selection of process parameters ,13. In tThere is a broad spectrum of infill patterns, making it difficult to analyze the influence of raster patterns. In this study, solid samples filled with a perimeter raster were analyzed, which is where shell thickness was selected long enough to fill the sample with a raster angle of 0° d. In othEach sample set consisted of five specimens for each orientation and material, with a total of 150 specimens for mechanical testing  and 45 specimens for dimensional and surface roughness characterization. Average values of the mechanical, dimensional and surface roughness tests were taken as the results. The manufactured specimens were stored in a dry box in order to minimize moisture absorption, which adversely affects the mechanical performance of PLA. Since the physical properties of many materials  can vary depending on ambient temperature, tests were carried out according to the standards for room temperature.A 50 kN universal electro-mechanical testing machine with a 5 kN load cell was used for the uniaxial tensile, 3-point bending and ILSS tests at a fixed loading rate of 2 mm/min, for both the tensile and 3-point bending tests, and 1 mm/min for short beam shear test (SBS) to obtain the ILSS strength. The selection of this displacement rate was in agreement with the displacement rate used in other studies ,13,39 an= 2.0 + 10L/1000 µm, where L is the machine axis length in mm. In addition, surface texture was measured using a 3D Surface Profiling System Talysurf CLI 1000 with a range of 100 mm in the three axes . The Talysurf CLI 1000 system uses an inductive contact gauge with a 2.5 mm Z-axis range and a resolution of 40 nm. In addition, surface texture was measured by sampling a 10 x10 mm2 area in a flat position on the surface center point of the workpiece upper face, taking 334 profiles separated 24 µm. The surface roughness parameters analyzed were the Arithmetic Mean Height (Sa) and the Maximum height (Sz) [Root Mean Square Flatness Deviation (Fltq) with Least Squares Reference Plane (LSPL) [For dimensional inspection, the optical measurement used a vision system Tesa-Visio 200 with a motorized zoom and CCD color camera. The axis ranges are X-200 mm, Y-100 mm, Z-150 mm, with a resolution of 0.001 mm; repeatability is defined by Ex, Ey ght (Sz)  and for e (LSPL) .t, σf) and stiffness  of the 3D printed PLA-based samples are tabulated in C) and the maximum interlaminar shear strength (τILSS) are tabulated in Average and standard deviation of the test results of the maximum tensile and flexural strength  as a function of the PLA material and build orientation. It can be observed that On-edge and Flat orientations showed higher values of impact strength than upright orientation. In the case of Flat samples, impact loading was parallel to the adjacent layers and they withstood most of the applied load. On the other hand, in the case of On-edge samples, impact loading was perpendicular to the individual layers, and they withstood most of the applied load. In addition, Flat samples exhibited the highest value of impact strength for the three PLA-based materials. These results were in line with those reported in references [ferences ,65 for uferences .Ec, of the PLA-Graphene specimens with PLA and PLA 3D850 specimens, it is observed that the impact strength, Ec, of PLA and PLA 3D850 samples was about 1.2–1.3 times higher than the maximum impact strength of PLA-Graphene composite samples. Hence, the addition of GNPs tended to reduce the impact strength of the PLA composite samples. This can be explained by the brittle behavior exhibited by the PLA-Graphene composite samples in On-edge and Flat orientations. On the other hand, in the case of Upright oriented samples, PLA-Graphene composite samples showed similar or even higher ductility and mechanical performance compared to PLA and PLA 3D850 samples. This trend indicates an enhanced interlayer adhesion and it is in agreement with the findings of the previous section.Comparing impact strength, The bonding performance of the different layers is a main factor for the mechanical strength of 3D printed thermoplastic parts. In addition, Finally, SEM examination of the cross-sectional ILSS samples was performed to obtain information on the interlayer performance. X-axis, Y-axis and Z-axis, respectively, showing the mean, the maximum and the minimum values of the three materials and build orientations analyzed in this study. The results of three samples of each set are shown. X-axis and Y-axis are related to the dimensional accuracy of deposited filaments in the same layer. On the other hand, Z-axis is associated with the dimensional accuracy of deposited layers. The results showed that the greatest differences in dimensional accuracy are linked with the build orientation. In the case of the X-axis, Flat and On-edge orientations depicted higher dimensional deviation than Upright orientation. More specifically, flat and on-edge PLA 3D samples showed a mean deviation of 288 ± 13 µm and 304 ± 16 µm, respectively, while upright PLA samples depicted a mean deviation of 78 ± 48 µm. The reason was that Upright orientation was affected by layer accumulation and a lower dimensional deviation was expected. In the case of the Y-axis, it depicted the highest mean dimensional deviation of all test with a maximum mean deviation of 407 ± 9 µm for Flat PLA-Graphene samples. These specimens showed defects in the middle layers of flat-oriented samples  reinforced composites manufactured by FFF technique have been analyzed. The effect of build orientation and graphene reinforcement were studied in particular. Tensile, three-point bending, Charpy impact and interlaminar shear strength tests were carried out to determine the mechanical response of the 3D printed specimens following ASTM standard recommendations. SEM images of ILSS failure samples were evaluated to determine the effects of GNPs on bonding performance.It has been shown that the effect of build orientation was of particular significance on the mechanical performance of PLA-based materials. On-edge and flat orientations showed the highest values for maximum tensile and flexural strengths and stiffness, while upright orientation resulted in the lowest ones. There were no significant differences between PLA and PLA3D850 in terms of tensile and flexural behavior. Furthermore, PLA-Graphene composite samples showed the best performance in terms of tensile and flexural stress and stiffness, except in the case of on-edge orientation. GNPs offered higher stiffness with respect to PLA matrix, preventing the shear strain. More specifically, PLA-Graphene composite showed a significant improvement of the tensile behavior over the other two materials in the case of upright orientation. However, the addition of GNPs tended to reduce the impact strength of the PLA composite samples. Finally, PLA-Graphene composite samples showed the highest interlaminar shear strength. These results were in accordance with the enhanced interlaminar adhesion and performance showed by the PLA-Graphene samples under tensile and flexural loading.Z-axis due to enhanced interlaminar performance. Finally, PLA-Graphene specimens showed, in overall terms, the best performance in terms of surface texture, particularly when parts were printed in flat and on-edge orientations.Moreover, the addition of graphene nanoplatelets did not affect, in general terms, the dimensional accuracy of the PLA-Graphene composite specimens. They showed, in overall terms, the best dimensional accuracy in The results have shown that it is still a challenge to increase the mechanical performance of 3D printed reinforced composite materials with respect to conventional polymer processing methods such as compression or injection molding. A compaction stage after the deposition of the filament would be desirable to reduce porosity. Nevertheless, the properties obtained by 3D printed reinforced composites by FFF are, in general terms, higher than the usual 3D FFF thermoplastics.In conclusion, using FFF to fabricate 3D printed composites with much higher mechanical performance has become a cutting-edge and interdisciplinary research topic in the last few years. It seems to be a very promising technology with potential for future development. It is a relatively new technique and there is a lack of experimental data on the mechanical performance of structures manufactured by this process, underscoring the need for further research to improve our understanding of the mechanical behavior of 3D printed composites.


GaN nanocolumns were synthesized on single-layer graphene via radio-frequency plasma-assisted molecular beam epitaxy, using a thin migration-enhanced epitaxy (MEE) AlN buffer layer as nucleation sites. Due to the weak nucleation on graphene, instead of an AlN thin-film we observe two distinguished AlN formations which affect the subsequent GaN nanocolumn growth: (i) AlN islands and (ii) AlN nanostructures grown along line defects (grain boundaries or wrinkles) of graphene. Structure (i) leads to the formation of vertical GaN nanocolumns regardless of the number of AlN MEE cycles, whereas (ii) can result in random orientation of the nanocolumns depending on the AlN morphology. Additionally, there is a limited amount of direct GaN nucleation on graphene, which induces non-vertical GaN nanocolumn growth. The GaN nanocolumn samples were characterized by means of scanning electron microscopy, transmission electron microscopy, high-resolution X-ray diffraction, room temperature micro-photoluminescence, and micro-Raman measurements. Surprisingly, the graphene with AlN buffer layer formed using less MEE cycles, thus resulting in lower AlN coverage, has a lower level of nitrogen plasma damage. The AlN buffer layer with lowest AlN coverage also provides the best result with respect to high-quality and vertically-aligned GaN nanocolumns. It is also reported that GaN thin-film is achievable on sapphire or amorphous substrates by employing either multi-layer or single-layer graphene as buffer layer14. Such exploitations can be realized by taking advantage of the weak quasi-van der Waals binding17 which can drastically relax the lattice matching condition to be satisfied by constituent materials. That being said, the lack of chemical reactivity of graphene and its extremely low surface energy18 greatly disrupt the nucleation process of GaN, resulting in a low nucleation density19 and difficulty in controlling the stacking sequence of the GaN growth3. The latter issue, which often manifests in the form of stacking faults5 or threading dislocations17, can possibly be suppressed by growing nanowire or nanocolumn structures25. Nevertheless, because of the absence of dangling bonds in graphene, nanocolumns are often aligned in non-vertical directions28 and/or have low density29. Both problems are required to be addressed in order to demonstrate that the growth of III-N semiconductor nanostructures, particularly nanocolumns, utilizing graphene as the substrate can be further considered as an alternative platform in enabling the advancement of optoelectronic device performance and functionality, for instance light-emitting diodes30.Recent progresses in the growth of GaN thin-film on grapheneex-situ manner14. However, the plasma treatments to prepare the growth of GaN on graphene in radio-frequency plasma-assisted molecular beam epitaxy (RF-PAMBE), which is typically done in-situ, often lead to the generation of more severe plasma-induced damage of graphene31. Moreover, it has been evidenced that the GaN nanocolumns may be randomly oriented if the growth is done directly on graphene28. The use of a thin AlN buffer layer can provide substantial protection to the graphene from the direct bombardment of nitrogen plasma and enable the growth of high-density, vertically-aligned GaN nanocolumns on graphene28. Therefore, it is now perceived that the understanding of AlN as an intermediate layer in the GaN/graphene system is necessary to grasp the growth behavior of the GaN nanocolumns in relation to the graphene properties at a given growth condition. Furthermore, it is expected that the insight towards these aspects can shed light on the preference of certain growth conditions over others, which later can be utilized for growing device structures.In this regard, the introduction of defects in graphene by means of plasma treatments could alleviate the issue of absence of dangling bonds in graphene. In case of GaN grown by metal-organic vapor phase epitaxy (MOVPE), the creation of dangling bonds in graphene by this method has been achieved via In the present work, we concentrate on the RF-PAMBE synthesis of self-assembled GaN nanocolumns on transferred single-layer graphene on silica glass for different AlN growth conditions. An insight towards the relation between the AlN migration-enhanced epitaxy (MEE) cycles and the morphology of the AlN buffer layer, as well as the resulting structural and optical properties of the grown GaN nanocolumns on graphene with AlN used as an intermediate layer, is reported. Additionally, the impact of the AlN buffer layer growth on graphene structural properties is presented.first feature is the nucleation of high-density and irregular AlN nanostructures along the line defects of graphene , which is similar to the cases of AlGaN nucleation by MOVPE on graphene29. Commonly, line defects observed in chemical vapor deposition (CVD)-graphene are wrinkles and grain boundaries34. In addition to the surface morphology of the copper foil and the transfer process34, the wrinkles are often related with the compressive stress caused by the difference in thermal expansion coefficients between graphene and the copper foil during cooling from CVD growth temperature to room temperature (RT)35. The grain boundaries are formed as a result of coalesced graphene grains which are grown on the different copper facets during the CVD growth process36. These areas of graphene likely contain defects, which can eventually create dangling bonds to support covalent/chemical bonding of atoms, resulting in a high nucleation density of AlN nanostructures on those particular graphene sites. From bird’s eye-view SEM images, one clearly sees how the nucleation of AlN nanostructures spreads further away from the line defects with the increase of MEE cycles . This will eventually cover the graphene surface, as shown in sample A2, and furthermore in sample A3.The morphology of the thin AlN buffer layer formed on the graphene surface using MEE by RF-PAMBE technique was studied as a function of the amount of AlN deposited, defined by the number of MEE cycles. Details concerning the growth parameters for the AlN buffer layer are outlined in Methods. Three different AlN samples, namely A1, A2 and A3, with respectively 20, 40 and 80 MEE cycles, were grown and characterized. Figures second feature is the formation of individual AlN islands . Unlike the high-density AlN nanostructures along the graphene line defects described above, their size are quite significant, with average diameters of approximately 70, 120 and 200 nm for samples A1, A2 and A3, respectively. In addition to the formation of individual AlN islands, it is also possible for the AlN islands to merge with their nearest vicinity to form coalesced AlN islands . A tendency for AlN to form an island (and its cluster formation) instead of a thin-film could be caused by the extremely low surface energy  of graphene18, which promotes the high surface tension on graphene surface. In addition, the lack of dangling bonds in these graphene surface areas hampers the AlN nucleation process to form a continuous thin-film structure, contrary to the formation of high-density AlN nanostructures in which the dangling bonds are provided by the defects along the graphene line defects. As opposed to this, when the MEE technique was applied to grow AlN on a sapphire substrate at a similar substrate temperature, it resulted in large island sizes and good coverage on the substrate surface37.The first group of features is the row of high-density vertical GaN nanocolumn growth , where nanocolumn diameters vary from 50 to 70 nm. More often, these nanocolumns are found to be grown very close to their neighbor, which is very likely to form coalesced nanocolumn structures, rather than single isolated nanocolumns. Such formation of coalesced GaN nanocolumn structures is clearly visible in sample G1. When formed on 40 MEE cycles AlN buffer (sample G2), it becomes more difficult to discern the rows of vertical GaN nanocolumns, since the density of the nanocolumn structures in general is increased. However, this unique pattern is still observable if one follows the GaN nanocolumns lining with each other, where the nanocolumns have a tendency to coalesce with their vicinity. Interestingly, GaN nanocolumns in sample G3, which has the highest number of AlN MEE cycles, do not meet the expectation of being the most coalesced nanocolumns, forming GaN nanowall-like structures, but rather display nanocolumn structures with identical diameters to those of sample G1.Further RF-PAMBE growth of GaN nanocolumns was then carried out on samples A1, A2 and A3, after which they were re-named as G1, G2 and G3, respectively. In order to gain insight into the influence of the AlN buffer layer on the formation of GaN nanocolumns, the growth conditions of GaN nanocolumns on samples G1, G2 and G3 were kept the same (described in Methods). The representative top- and bird’s eye-view SEM images for samples G1, G2 and G3 are given in Fig. second group of features is the individual vertical GaN nanocolumns . It appears that the number of MEE cycles during AlN formation affects the diameter of the grown nanocolumns, where less cycles give smaller diameter. It is found that the GaN nanocolumns in samples G1, G2 and G3 show average diameters of 90, 130 and 210 nm, respectively. Additionally, it is discovered that there are certain nanocolumns  whose diameter is considerably larger than the mentioned average values. Some of them seem to result from single nanocolumn growth which eventually merges with other nanocolumns in its proximity forming an irregular shape, while there are also circular-shaped nanocolumns where the coalescence process likely starts immediately from the nucleation stage. It should be remarked that GaN nanotubular-like structures (white outlines) can also be formed38 because the edge of the AlN islands can initiate GaN nanocolumn growth39. The third group of features is the formation of tilted nanocolumns . Simultaneous energy dispersive spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) were carried out on the same area to map all present elements. The Ga, Al and O element maps are combined into a color map in Fig. A separate nanocolumn sample was synthesized with nominally the same growth conditions as sample G1 for transmission electron microscopy (TEM) measurements. The cross-sectional high-angle annular dark field scanning TEM (HAADF STEM) image of Fig. A higher magnification of the GaN nanocolumn interface area  of the GaN crystal, it indicates that sample G1 with 20 AlN MEE cycles has the highest density of vertical nanocolumns (since the SEM characterization presented above show that G1 has the lowest average GaN nanocolumn diameter [90 nm] among the G-samples). We note that whereas the peak intensity of the AlN 0002 reflection is higher for sample G2 than for sample G1, there is not much difference in this peak between sample G2 and sample G3, despite higher number of AlN MEE cycles for sample G3 and improved graphene coverage surface area  scans presented in Fig. The ω (rocking) scans of the GaN, shown in Fig. 24. For sample G3, the grown GaN nanocolumns characterized with lower density , (557.9 ± 0.9) and (566 ± 1.0) cm−1. These wave numbers correspond well to the established A1 ), E1 (TO) and E2 (high) phonon modes of wurtzite GaN, respectively53. In line with the former results, the as-grown GaN nanocolumns in samples G1, G2 and G3 likewise exhibit almost identical spectra. As presented in Fig. −1. In addition, the E2 (low) phonon mode  mode at 566.2 cm−1 and its small FWHM  and Si(111)54) correspond to the FWHM of a fully relaxed thick free-standing GaN layer55, which can be an indicator of the high crystalline quality of the GaN nanocolumns. Furthermore, the TO phonon mode at 555 cm−1 related to zinc blende GaN51 is not detected in any of the GaN nanocolumn samples. However, expected A1  and E1 (LO) phonon modes of GaN51 at 734 and 741 cm−1 are not visible in any of the GaN nanocolumn samples, similar to the results obtained by Robins et al.48 and Jeganathan et al.52. Instead, we notice very weak peaks at 715 cm−1 and 743 cm−1  and the 2D band (2680 cm−1) with an intensity ratio of I2D/IG ≈ 2, while the disorder-induced D band (1342 cm−1) is barely seen, making the intensity ratio of ID/IG almost negligible. Changes to the aforementioned intensity ratios, peak positions and possible generation of another band are observed in all of the GaN nanocolumn samples (whereas a faint G* band at ~2456 cm−1 is unaffected). Firstly, the most prominent changes are the decline of the I2D/IG ratio along with an increasing ID/IG ratio from sample G1 to G2 and G3, implying that graphene becomes more defective as the number of AlN MEE cycles increases from 20 to 80. Secondly, another defect-related signature in graphene at 1619 cm−1, known as D’ band56, is noticed only in sample G3. Finally, the peak positions of the D, G and 2D bands experience slight blue shifts, indicating a compressive strain and/or a modification of the carbon atoms in the graphene network by the incorporation of nitrogen atoms which could lead to an n-type doping57. Such blue-shifting peaks have been observed when an intentional plasma nitridation of graphene using either nitrogen58 or ammonia59 causes the introduction of defects as well as changes in the chemical and electronic properties of graphene. Indeed, in this work such nitridation process is an inevitable part of the GaN nanocolumn growth in RF-PAMBE, although during the AlN buffer layer formation the exposure of nitrogen plasma is intended for the nitridation of Al. As shown in Fig. In comparison with the pristine graphene reference sample (i.e. sample before any III-V growth), graphene structural properties after the GaN nanocolumn growth demonstrate quite significant alterations, as can be seen in Fig. e G band 586 cm−1 From the growth observation on the synthesis of GaN nanocolumns on graphene utilizing AlN buffer layers grown via MEE technique with 20, 40 and 80 cycles, it can be suggested that their morphology and orientation are restrained by the AlN structures on graphene. The high surface tension of graphene creates AlN islands on the graphene surface, beneficial for nucleation of GaN nanocolumns. Along with the islands, AlN nanostructures are densely formed along line defects (grain boundaries or wrinkles) of graphene due to the existence of defects which provides dangling bonds. Vertical GaN nanocolumns can be consistently obtained from the AlN islands independent of the number of AlN MEE cycles, whereas the GaN nanocolumns formed on AlN nanostructures can be randomly oriented when they are grown with higher number of AlN MEE cycles. There is also a likelihood of limited direct growth of GaN nanocolumns on graphene, resulting most likely in random growth orientations. Although higher number of MEE cycles produce wider AlN coverage on graphene, the subsequent GaN nanocolumns as well as the graphene property turn out to be not ideal. The structural characterizations and optical measurements present that GaN nanocolumn formation utilizing AlN buffer layer formed with 20 MEE cycles is the most preferable growth condition to obtain overall good quality and vertical alignment of GaN nanocolumns while maintaining the least damage on graphene.2 CVD-graphene grown on copper foil34 and transferred onto the center of a 2-inch supporting silica glass wafer (thickness of 0.5 mm) by Graphene Platform Corp.  was used as growth substrates. All the graphene substrates used in this work refer to an atomic layer of sp2 hybridized carbon atoms arranged in a hexagonal structure with an approximate thickness of 0.335 nm. The samples were grown by an EpiQuest RF-PAMBE system (at Sophia University) equipped with an RF nitrogen plasma source to generate active nitrogen and standard solid-source effusion cells (Knudsen cells) to provide Al, Ga and Si atoms.Commercially available 10 × 10 mm60 at 805 °C, with expectation that the migration length of the supplied atoms on the substrate surface becomes longer than when using the conventional MBE method. Stated substrate temperatures were measured by a pyrometer [ref. –5 Pa, a N2 flow rate of 2.0 sccm and an RF power of 450 W. Each MEE cycle (or MEE period) of AlN consists of four seconds with Al atom supply, five seconds of interruption (resting time) and three seconds with N atom supply27. To investigate the effect of the AlN buffer layer, we grew AlN buffer layer samples A1, A2 and A3 with different layer thicknesses by employing 20, 40 and 80 MEE cycles, respectively. After SEM characterization, these samples were re-loaded into the RF-PAMBE growth chamber and further growth of GaN nanocolumns was performed with conventional MBE method using the following growth parameters28: a Ga flux of 2.5 × 10−4 Pa and a N2 flow rate of 2.75 sccm (RF power of 450 W) at a substrate temperature of 895 °C with a growth duration of 90 minutes. After the growth of GaN nanocolumns on samples A1, A2 and A3, the samples were re-labeled as G1, G2 and G3, respectively.In general, the growth was started by depositing the AlN buffer layer using the MEE techniqueter ref. . MEE wasSEM images were obtained using an SII SMI3050SE focused ion beam-SEM and a Hitachi SU8000 SEM at acceleration voltages of 15 and 10 kV, respectively.The interface of nanocolumn/buffer layer/graphene/silica glass and their element distribution were studied by high-resolution TEM and STEM-EELS in a double Cs-corrected cold field emission gun JEOL ARM200F operating at 200 kV, equipped with a QuantumER GIF for EELS. Details on the TEM specimen preparation can be found in ref. HRXRD was performed with a Bruker D8 Discovery High-Resolution Diffractometer using Cu Kα radiation (1.5406 Å).6 cm−2) was used as the reference sample like for previous studies24.Optical studies were done using RT micro-photoluminescence with a He-Cd laser (325 nm) as the excitation source. A freestanding HVPE-grown GaN bulk substrate (threading dislocation density of 6–8 × 10Unpolarized micro-Raman spectroscopy was conducted at RT in backscattering configuration using a Renishaw InVia Reflex Spectrometer System equipped with a 514.5 nm excitation laser. A pristine graphene transferred onto silica glass was utilized as a comparison to graphene samples after RF-PAMBE growth.


In this paper, we report the finite element method (FEM) simulation of double-clamped graphene nanoelectromechanical (NEM) switches. Pull-in and pull-out characteristics are analyzed for graphene NEM switches with different dimensions and these are consistent with the experimental results. This numerical model is used to study the scaling nature of the graphene NEM switches. We show the possibility of achieving a pull-in voltage as low as 2 V for a 1.5-μm-long and 3-nm-thick nanocrystalline graphene beam NEM switch. In order to study the mechanical reliability of the graphene NEM switches, von Mises stress analysis is carried out. This analysis shows that a thinner graphene beam results in a lower von Mises stress. Moreover, a strong electrostatic force at the beam edges leads to a mechanical deflection at the edges larger than that around the center of the beam, which is consistent with the von Mises stress analysis. The standby power consumption of conventional complementary metal-oxide semiconductor (CMOS) circuits increases to the dynamic ON state level as they are scaled down to the scale of a few tens of nanometers . On the Graphene is a two-dimensional material with excellent mechanical stability and electrical conductivity, and a high Young’s modulus of ~1 TPa . These oIn this work, we present a three dimensional (3D) finite element method (FEM) simulation of double-clamped nanocrystalline graphene beam NEM switches. We focus on designing the graphene NEM switch in line with the experimental work . The pul2 substrate using plasma-enhanced chemical vapor deposition (PECVD) [2- and sp3-hybridized carbon atoms. The deposited NCG film is polycrystalline in nature [L, width W, and thickness t, and a top metal electrode. The schematic representation of the device is shown in In this section, we briefly describe the geometry and operation principles of NEM switches. In our earlier work , we expe (PECVD) . The NCGn nature . The poln nature . The mecn nature . Moreoven nature . The NCGn nature . The poln nature . Usuallyn nature . The pron nature . We usedn nature . For theg0. As the voltage applied between the suspended graphene beam and the top electrode is increased, the resulting electrostatic force balances with the elastic restoring force of the deformed graphene. When the applied voltage reaches a critical point, the electrostatic force overwhelms the restoring force, which causes the graphene beam to be pulled towards the top electrode/fixed element, resulting in closing the switch and thereby leading to a sharp rise in the current flow through the device [The initial air gap of the device is e device . When thThe static electrical and mechanical characteristics of the NEM switch were simulated using the FEM-based CAD tool IntelliSuite  . Figure t = 3, 5, and 9 nm. t = 9 nm, 5 nm, and 3 nm, respectively. This result shows a clear dependence of the pull-in voltage on the scaling of the thickness of the suspended graphene beam. Thus, we confirm that the introduction of thickness scaling leads to a reduction of the pull-in voltage.The von Mises yield criterion is a general way to estimate the yield of any ductile material, such as metals ,24. The NEM switch C has a maximum von Mises stress of 6.2 GPa. When the length of the graphene beam is increased to 1 μm and 1.5 μm, it leads to a decrease in the von Mises stress of 3.8 GPa and 2.3 GPa, respectively. Furthermore, the maximum stress for NEM switch A is 2.5 GPa; when the thickness of the graphene is reduced to 5 nm and 3 nm, the stress is decreased to 1.4 GPa and 0.9 GPa, respectively. V, and the electric field, E, in the free space can be obtained by solving Poisson’s equation [To analyze the impact of the applied electric field on the double-clamped graphene beam NEM switch, we made the same model in COMSOL Multiphysics  . The NEMequation . Figure Z direction at 5 nm above the bottom electrode for the different applied voltages. Consistent with In this paper, we have studied the electro-mechanical switching and mechanical reliability of graphene beam NEM switches by FEM simulations. To evaluate the mechanical reliability of a graphene beam NEM switch, we scaled the length and thickness of the graphene beam and studied the von Mises stress for each structure. This analysis showed that the graphene beam NEM switch with a longer length of 1.5 μm and a thickness of 3 nm has a pull-in voltage of 2 V. The electrostatic force concentration at the edges of the graphene beam leads to more mechanical deflection at the edges than at the center of the beam.


The liquid-phase exfoliation of graphite is one of the most promising methods to increase production and commercial availability of graphene. Because ionic liquids can be easily obtained with chosen molecular structures and tuneable physicochemical properties, they can be use as media to optimize the exfoliation of graphite. The understanding of the interactions involved between graphite and various chemical functions in the solvent ions will be helpful to find liquids capable of dissociating and stabilizing important quantities of large graphene layers. After a step of sonication, as a mechanical precursor, samples of suspended exfoliated graphene in different ionic liquids have been characterized experimentally in terms of flake size, number of layers, total concentration and purity of the exfoliated material. Nine different ionic liquids based on imidazolium, pyrrolidinium and ammonium cations and on bis(trifluoromethylsulfonyl)imide, triflate, dicyanamide, tricyanomethanide, and methyl sulfate anions have been tested. UV-vis, Raman and X-ray photoelectron in addition to high resolution transmission electron and atomic force microscopy have been selected to characterize suspended exfoliated graphene in ionic liquids. The number of layers in the flakes exfoliated, the size and concentration depend of the structure of the ionic liquid selected. In order to obtain large flake sizes, ionic liquids with bis(trifluoromethylsulfonyl)imide anions and a cation with an alkyl chain of medium length should be selected. Smaller cation and anion favors the exfoliation of graphene. The exfoliation caused the formation of C-H bonds and the oxidation of the graphitic surface. Today, two approaches are known to produce graphene: in “bottom-up” methods, such as chemical vapor deposition (CVD), graphene is synthesized, whereas in “top-down” methods, for example liquid-phase exfoliation, graphene sheets are separated from bulk material. The first approach produces low quantities with high quality and large flakes. The second method (top-down) using graphite is low in cost and yields a high concentration of suspended flakes but fabricates limited-size sheets with a low yield of mono-layer graphene. The development of technologies to produce large quantities of high-quality exfoliated graphene is important. One way to achieve a large scalable production is to improve methods of the liquid-phase exfoliation of graphite.Since its isolation in 2004  has stabilized a high concentration of graphene flakes compared to other solvents  are liquid salts below 373 K Seddon, , general4C1im][Ntf2]) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide . The exfoliation conditions are summed up in 6C1im][PF6]) was also used to exfoliate graphite using an ultrasound technique  has been reported in ILs with promising results. In 2010, Wang et al. (1im][Ntf2]), [C4C1im][Ntf2], 1-benzyl-3-metylimidazolium bromide ([BnzC1im][Br]) and 1,3-bis(phenylmethyl)imidazolium bis(trifluoromethylsulfonyl)imide ([(Bnz)2im][Ntf2]). The concentration of graphene in suspension was measured by UV-vis absorbance spectroscopy. [BnzC1im][Br] has a viscosity that was judged too high to disperse graphite. The concentration of suspended graphene in the [C4C1im][Ntf2] was too low to be detected by absorbance with the author's set up. [(Bnz)2im][Ntf2] stabilized a larger amount of graphene over [BnzC1im][Ntf2] 2im][Ntf2] were found oriented parallel to the surface of graphene unlike the single benzyl substituent in [BnzC1im][Ntf2] im][PF6], was exfoliated using microwaves during 0.5 h. The mixture reached the temperature of 443 K. By proton NMR the authors showed that 10% of the IL was degraded. Graphene had no additional structural defects and 95% of the flakes produced were single-layer graphene. The same protocol was used in [C4C1im][PF6] but with a lower exfoliation rate.In 2015, Matsumoto et al.  was used to analyse the surface showing that the IL intercalated between graphene layers and that the cation preferentially interacts with the surface of graphene compared to the anion. One explanation is that the C2C1im+ cation is not very large and can be interposed between two layers of graphene. Also the interfacial energy between the IL and graphene is comparable to that between two stacked graphene sheets.In 2016, Elbourne et al.  studied in this work are listed in Natural graphite flakes were purchased from Alpha Aesar with a 99.8% purity and a size inferior to 325 mesh. Raman spectroscopy and X-ray diffraction (XRD) were performed, without any treatment, to verify the initial purity  for 24 h. The ultrasonic water bath warmed up during use and reached a maximum temperature of 328 K. This thermal energy expanded the graphite layers and made the exfoliation process easier. As we worked with ILs, this temperature increase did not cause degradation of the solvent. Thus, the water bath was not cooled but was maintained at 323 ± 5 K. The horizontal distribution of the ultrasound is not homogeneous in the bath  solutions were prepared by adding graphite flakes to 2 mL of IL at an initial concentration of 5 mg.mL4C1im][AOT]) from Brown et al. sulfosuccinate  using a MET JEOL 2100FEF (field effect gun energy filtering) microscope with a point resolution of 0.23 nm without removing the IL. First, a thin film of SEG in IL was deposited on a copper mesh 200 grid coated with a layer of formvar/carbon. The grid was then dried gently with a filter paper. The liquid films were observed using an acceleration voltage of 200 kV. For each sample, five squares of the grid were analyzed. High resolution transmission electron microscopy, HRTEM, analysis was also performed on some particles using the same microscope. Subsequently, the HRTEM images and their crystal structure were determined from the diffraction pattern seen in the Fourier Transform images.−1 in the range of 1,200–2,900 cm−1.A volume of 1 mL of SEG was filtered through a polyvinylidene fluoride (PVDF) hydrophobic membrane (from Durapore) with a 220 nm pore size. The membrane was washed with dichloromethane and isopropanol (IPA) to remove the IL from the exfoliated graphite. Then, the filter was dried at 463 K during 12 h. This filter with exfoliated graphite was analyzed by Raman spectroscopy. Raman spectra were recorded at 294 K on a Jobin Yvon T64000 spectrophotometer equipped with a Olympus confocal microscope (100 × objective lens) with a CDD multichannel detector cooled with liquid nitrogen. The excitation source was a 514.5 nm ionized argon laser (Spectra Physics) line. The laser power was adjusted to 200 mW . Spectral resolution is at 0.7 cm2). The Si/SiO2 wafer had been previously washed in IPA during 30 min in an ultrasonic bath. After coating with the exfoliated graphene, the wafer was dried at 463 K for 2 h. The lateral and vertical size of the particules on the wafer were measured by AFM  were casted by spin coating at 1,000 rpm onto a silicium wafer  and Lorentzian (20%) distributions. The analyzed covered a surface of approximately 100 μm2 with a depth of 5 nm.XPS analysis was performed with Versaprobe II PHI 5000(ULVAC-PHI) spectrometer using a 100 μm focused monochromatic Al-Kα X-ray source (1486.6 eV) beam. The high-resolution spectral analysis was performed using a pass energy of 23 eV allowing an energy resolution of 0.5 eV. The XPS spectra were fitted by using Multipak VThe Potentiel of Mean Force (PMF), calculated in this work, corresponds to the reversible work required to peel one layer of graphene from a stack of four layers in different ILs. The method and set up of these PMF calculations by molecular dynamics have been described in a previous paper  among the nine studied ILs. In the ILs with other anions, the concentrations are below 0.5 mg.mL−1 and lower than in ILs with the 4C1im][C(CN)3], [C2C1im][Otf] and [C2C1im][N(CN)2] ILs presented the lowest concentrations of SEG. The relatively high error bars make the distinction between ILs with the 1im][Ntf2] and also in [C4C1im][Ntf2] with a different set up. After exfoliation, no nano-carbon object was found in [C4C1im][Ntf2] and 0.81% of SEG in [BnzC1im][Ntf2]. The low and similar concentrations of SEG reported in these two ILs hinders comparison with our results. Our main conclusion is that using a The [Ci et al.  exfoliat4C1im][C1SO4] which is the IL with the highest viscosity, the concentration of SEG is lower than in the ILs based on the −3. ILs with densities around 1.4 g.cm−3 seem to be favorable to suspend exfoliated graphite, this conclusion being a simple observation and does not necessarily imply causation.In −1 leads to higher concentrations of SEG. In a previous work 3] lead to similar lateral size profiles and to approximately the same amounts of suspended material. We conclude that ILs with the Flakes of exfoliated graphite have larger sizes in [Ntf2], [Ntf2], [C2C1im][N(CN)2], [Ntf2] and [C10C1im][Ntf2] are similar to that of bi-layer graphene, as we can observe a shoulder in According to the literature  distance in the hcp structure. Indeed, it is shown in via AFM depends on the substrate and on the experimental conditions . For example, on Si/SiO2, graphene can show an apparent height of 1 nm 3]. Fifty percent of the exfoliated graphene is in fact graphite with more than 30 flakes while in [C2C1im][Otf], 30% of graphene with <5 layers is found. Using 2C1im][Otf] > [C4C1im][C1SO4] > [BnzmC1im][Ntf2] > [Ntf2] ≃ [C4C1im][Ntf2] > [C4C1im][C(CN)3].The SEG were also analyzed by high resolution TEM to identify monolayers of graphene. The choice of the anion seems important to control the degree of exfoliation of SEG. Adding a benzyl function instead of an alkyl chain on an imidazolium head group will reduce the lateral size of flakes but will favor a higher concentration of graphene.2, sp3 and oxydated carbon atoms at the surface of exfoliated graphite, XPS measurements were performed in samples of washed SEG deposited on a PVDF membrane. Based on references samples studies, we performed C1s core level fitting for exfoliated graphite in different ILs media. In exfoliated graphite, we assigned five main contributions, graphitic carbon (CCgraph) at 284.3 eV, IL related carbon , PVDF related peaks (CCH2 and CF2 at 286.3 and 290.5 eV), carbon sp3 at 284.9 eV and carbon oxyde related peak (C–O and COO at 286.0 and 287.5 eV). 4C1im][Ntf2]. The XPS spectrum of natural graphite is presented in the 3], formation of C-H bonds and oxidation of at least 60% of carbon were found at the surface of the carbon material.The purity of SEG in [Ntf2] was sonicated during 24 h. No differences were found between the XPS spectra of the IL before and after sonication, as shown in the  of peeling graphene in ILs was calculated from MD simulations and is plotted in 4, 1, 1, 1][Ntf2] has demonstrated worst results than [C4C1im][Ntf2], in term of concentration, lateral size and number of exfoliated layers.The PMF curves also indicate that the intercalation of [Ntf2] between two layers of graphene requires more energy than [C4C1im][Ntf2].In In order to attain a more complete view of suspended graphene in ILs, different techniques were used to characterize graphene flakes produced by solvent exfoliation of graphite.The concentration of suspended exfoliated graphene (SEG) is related to the stabilization step. UV-visible spectroscopy measurements reveal that the ILs with 4C1im][Ntf2] and [Ntf2] lead to larger flakes compared to [BnzmC1im][Ntf2] whereas smaller SEG flakes were found in [C2C1im][Otf]. A bulky anion seems to be an advantage to stabilize larger flakes. The number of stacked layers in flakes determined by AFM was smaller in [C2C1im][Otf].AFM and TEM measurements allowed to determine the lateral size of graphene flakes, showing that [C3 hybridization of carbon. [C2C1im][Otf] leads to the highest degree of oxidation compared to the others ILs studied. This result could explain the efficiency of this IL to exfoliate graphite down to single layers. Using an ultrasonic bath to process the exfoliation of graphite does not seems to be the best technique to produce a high concentration of pristine graphene. To optimize the exfoliation process, we need first to increase the reproducibility of the sonication/centrifugation procedure used in this work in order to increase the initial concentration and size of graphite flakes significantly.Exfoliation of graphene in ILs using ultrasound caused surface changes mainly oxydation but also spAdding π-π interactions between the IL and the carbon material does not seem to improve the exfoliation process. With these results, the design of the IL can be optimized by choosing a EB conducted the experiments jointly with BM (TEM), CS (TEM and EIS), DB and P-OB (AMF), AB . MG and AP supervised the project. The manuscript was written by EB, MG, and AP with inputs from all authors.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


We studied the effect of low and high sialylated IL4–10 fusion protein (IL4–10 FP) on In vivo activity was assessed in an inflammatory pain mice model upon intrathecal injection.CHO cell lines producing low (IL4–10 FP lowSA) and high sialylated (IL4–10 FP highSA) fusion protein were generated. Bioactivity of the proteins was evaluated in an LPS-stimulated whole blood assay. Pharmacokinetics were studied in rats, analyzing plasma levels of IL4–10 FP upon intravenous injection. in vitro. The pharmacokinetics study showed a 4-fold higher initial systemic clearance of IL4–10 FP lowSA, whereas the calculated half-life of both IL4–10 FP lowSA and IL4–10 FP highSA was 20.7 min. Finally, both IL4–10 FP glycoforms inhibited persistent inflammatory pain in mice to the same extent.IL4–10 FP lowSA and IL4–10 FP highSA had similar potency in vitro and in vivo activity, but clearly results in a difference in systemic exposure. The rapid systemic clearance of low sialylated IL4–10 FP could be a favorable characteristic to minimize systemic exposure after administration in a local compartment.Differential sialylation of IL4–10 fusion protein does not affect the  Interleukin-4 (IL-4) and IL-10, well-known anti-inflammatory cytokines, have potential for the treatment of inflammatory diseases. However, clinical studies with IL-4 or IL-10 have been disappointing ,6. IL4–1in vitro. In whole blood and peripheral blood mononuclear cell (PBMC) cultures IL4–10 FP strongly inhibits the production of LPS-induced pro-inflammatory cytokines such as IL-1β, TNF, IL-6, and IL-8, while having minimal, if any, effect on the production of IL-1RA and sTNFR (ex vivo and in vivo. The fusion protein inhibits pro-inflammatory cytokine production by rheumatoid arthritis (RA) and osteoarthritis (OA) synovial tissue and cartilage cultures  supplemented with 4 mM L-glutamine (Gibco) with pluronic F-68 (Life Technologies), at 0.1 or 0.2%, w/v (culture medium) in a humidified CO2 incubator. Cell number and viability were assessed with a CASY counter (Roche Innovatis AG). Levels of IL4–10 FP produced by the cells were measured in the supernatant with a human IL-10 ELISA kit  according to manufacturer’s instructions.CHOBC® cells were transfected with a proprietary expression plasmid containing cDNA encoding IL4–10 FP, and with a plasmid with cDNA encoding α2,3-sialyltransferase (ST3GAL_IV) using an AMAXA Nucleofector II device (Lonza). After transfection, cells were pooled and seeded at 1.0 × 106 viable cells (vc) per ml culture medium in T-flasks. Cells were incubated for 48 h and seeded in 96-well plates at 300 to 3000 vc/well in culture medium supplemented with Zeocin (Invitrogen) and Blasticidin (Invitrogen) (selection medium). The cells were incubated for ~3 weeks. Visible cell clones were then transferred into 24-well plates containing 2 ml fresh selection medium and screened for IL4–10 FP levels (IL-10 ELISA). Best producing clones were selected, cultured in 6-well plates and expanded into 25 ml T-flasks (4-day culture). Subsequently, they were adapted to culture under shaking conditions and cultured for 7 days while cell density, viability and production were monitored at various intervals (7-day culture). In addition, sialylation of IL4–10 FP produced by different clones was analyzed using lectin-based ELISAs (see below). Finally, two cell lines producing IL4–10 FP with respectively low and high sialylation were selected.To generate IL4–10 FP producing cell lines, CHOBC® clones was evaluated using ELISA-type assays with the galactose-binding Erythrina Cristagalli Lectin (ECL), or the α2,3 sialic acid binding Maackia amurensis Lectin II (MAA). CHOBC® cell supernatant to be tested was diluted in PBS to yield a concentration of 10 μg/ml IL4–10 FP. 100 μl of diluted supernatant was coated in duplicate in the wells of maxisorp plates (Nunc). After O/N incubation at 4°C, plates were washed 3 times with PBS containing 0.05%, w/v, Tween-20 (Merck), followed by incubation with 200 μl/well PBS 0.1%, w/v, Tween-20 (PBS-T), 1 h at room temperature (RT), while gently shaking (300 rpm). 100 μl of biotinylated ECL or MAA (Vector Laboratories), diluted 1 to 10.000 and 1 to 3000 in PBS-T, respectively, were added to the plates, which were subsequently incubated for 1 h at RT. Bound biotinylated lectins were detected by incubation with Streptavidin poly-HRP  in PBS-T for 30 min at RT, followed by incubation with TMB (Invitrogen). The reaction was stopped with 1 M H2SO4 and the absorbance at 450 nm was measured. The ratio MAA/ECL, calculated using the OD450 values of bound MAA and bound ECL, is indicative for the sialylation ratio of the IL4–10 fusion protein.Sialylation of IL4–10 FP produced by the CHOw/v, Bovine Serum Albumin (BSA), and then equilibrated with PBS without BSA. Concentrated conditioned medium containing IL4–10 FP was loaded on the column, which was then washed with PBS. Bound IL4–10 FP was eluted with 0.1 M Glycine, pH 2.25. Fractions were immediately neutralized with 1 M Tris, pH 9.0 and dialyzed in PBS. Fractions containing IL4–10 FP were pooled, assessed for purity and protein content by running a protein gel (see below), a BCA protein assay (Thermo Scientific) and the IL-10 ELISA, aliquoted and stored at −80°C until further analysis.IL4–10 FP was purified from conditioned medium using affinity chromatography according to a previously published protocol . In shorw/v, Tween-20 (PBS-T). The membrane was incubated with the primary Ab mouse anti-human IL-4  or mouse anti-human IL-10 , in 1% milk in PBS-T, followed by HRP-conjugated goat anti-mouse IgG . To visualize the bands ECL Western blotting substrate was added according to manufacturer’s protocol . Stained protein gels and Western blots were imaged using the ChemiDoc MP system (BioRad).Cell supernatants were diluted 1 to 1.33 in Laemmli sample buffer (BioRad), containing 100 mM Dithiotreitol (Sigma-Aldrich), incubated for 10 min at 100°C, whereafter 10 ul was loaded on a 12% polyacrylamide Gel . After electrophoresis, the gel was either stained with Instant Blue (Expedeon) for visualization of total protein content, or prepared for Western blotting in order to specifically detect IL4–10 FP. Blotting was performed using the Trans-Blot system (BioRad) in combination with a 0.2 μm nitrocellulose-membrane Transfer Pack (BioRad), according to manufacturer’s instructions. After transfer, the membranes were blocked in 4% milk  in PBS 0.1%, 2, culture supernatant was collected and tested for TNF concentration with ELISA . The percentage inhibition was calculated relative to TNF production by LPS in absence of IL4–10 FP.Heparinized human blood obtained from healthy volunteers was diluted 1:10 in RPMI1640 medium (Invitrogen), supplemented with 1% penicillin/streptomycin  in 48-well culture plates (Nunc). Lipopolysaccharide  was added at 10 ng/ml, as well as low and high sialylated IL4–10 fusion protein at 0.01–3 nM (0.3–270 ng/ml), final concentrations. As control, HEK293 produced IL4–10 fusion protein was taken along  according to manufacturer’s protocol. Effectiveness of deglycosylation was monitored by Western blotting.1/2 = 0.693*(V/CL), where V is the distribution volume (ml) and CL is the clearance rate (ml/min).Clearance of IL4–10 FP from the circulation was studied in Wistar Crl:WI female rats . The study was approved by the animal ethical committee (project number AVD11500201744) and performed at the animal facility of the Utrecht University. Rats were acclimatized for 1 week prior to the experiment. Rats were intravenously injected via the tail vein with 5 μg IL4–10 FP lowSA or IL4–10 FP highSA, or with a mixture of 5 μg IL-4 (eBioScience) and 5 μg IL-10 (Invitrogen) in a volume of 200 μl PBS. Some rats were injected intravenously with 30 mg asialofetuin (Sigma-Aldrich) in 0.5 ml PBS 10 min prior to injection of low sialylated IL4–10 FP, to saturate the ASGPR. Blood was collected from the tail using a winged infusion system (150 ul per timepoint) in lithium-heparin tubes (Sarstedt) either at 5, 15, 30 and 120 min, or 10, 20, 60 and 120 min after injection of IL4–10 FP and plasma was prepared by centrifugation for 5 min at 2000 g. IL4–10 FP and IL-10 levels were measured with the IL-10 ELISA. IL-4 levels were measured with a human IL-4 ELISA  according to manufacturer’s instructions. Pharmacokinetics were evaluated using non-linear mixed effects modeling (with NONMEM v.7.3). Models were parameterized in terms of fixed effects (population mean) and two levels of random effects; per subject  and per measurement . A one-compartmental model with linear elimination was used as a structural model. Herein, clearance was assumed to be different for IL-10, IL-4, and IL4–10 FP. For IL4–10 FP, the clearance was further differentiated into a slow and fast route, where the fast route represented rapid ASGPR-mediated clearance. The fraction of the dose administered that eliminated via the fast route was estimated separately for high and low sialylated IL4–10 FP. For the rats that received asialofetuin prior to injection with IL4–10 FP, the proportion fast clearance was assumed to be zero. The 95% confidence interval of parameter estimates were calculated by sampling-importance-resampling (SIR). Half-life was calculated using the formula: Tn = 9 for both groups) or vehicle  was injected intrathecally. Mechanical hypersensitivity was measured using von Frey hairs (Stoelting), and the 50% paw withdrawal threshold was calculated using the up-and-down method  as a result of the 4-day culture and 4.2 pcd during the 7-day culture. For CHO372, the specific IL4–10 FP productivity was 3.9 and 3.7 pcd during 4-day culture and 7-day culture, respectively Fig. . These r). Purification of IL4–10 FP lowSA and IL4–10 FP highSA from culture medium using affinity chromatography via an anti-IL4 antibody recovered ~50% of the recombinant protein and yielded ~90–95% purity (data not shown). Both IL4–10 FPs inhibited LPS-induced TNF production in whole blood in a concentration dependent manner, with maximal inhibition at 3 nM . The inhibitory activity was comparable between IL4–10 FP lowSA and IL4–10 FP highSA. Furthermore, both glycoforms inhibited LPS-induced TNF production similar to that of HEK293-produced IL4–10 FP (used in our previous in vitro and in vivo studies)  . These dstudies) . These rIn a pharmacokinetics study we investigated whether the differential sialylation of IL4–10 FP affects its clearance from the circulation. Each IL4–10 FP preparation was injected in rats intravenously (5 μg via the tail vein), and the circulating concentration of IL4–10 FP in serial plasma samples was assessed by ELISA.Concentrations of IL4–10 FP showed an initial rapid decrease upon administration of IL4–10 FP lowSA presumably reflecting fast hepatic clearance Fig. . Adminisin vivo. Intrathecal injection of IL4–10 FP produced in HEK293 cells reduces pain in various mouse models, including models for persistent inflammatory pain . Blockade of the ASGPR with asialofetuin  in rats Although the initial clearance of IL4–10 FP lowSA differed from that of IL4–10 FP highSA, the terminal serum half-life for both IL4–10 FP lowSA and IL4–10 FP highSA were similar. This result is likely due to the presence of a fraction of IL4–10 FP with sialylated galactose-residues in the batch of IL4–10 FP lowSA. Indeed, glycan analysis of IL4–10 FP lowSA, though predominantly showing ECL binding, revealed significant MAA binding too, pointing to the presence of galactose-residues capped with sialic acids.vs 15 kDa). This difference in size impacts the clearance via the kidneys that is mainly affected by the size and the charge of a protein. IL4–10 FP highSA is expressed as a dimer with a molecular weight of ~70 kDa7. Indeed, we observed a considerably increased serum half-life of IL4–10 FP highSA (approximately 21 min), which underlines the contribution of the molecular weight to the clearance rate.Pharmacokinetics in humans of both IL-4 and IL-10 have been studied and indicated a relative short half-life for both cytokines. The apparent serum half-life of recombinant human IL-4 is 19 minutes , while tin vitro potency and different clearance from the circulation. Importantly, both forms effectively reduce inflammatory pain upon local, intrathecal administration. Thus, IL4–10 FP lowSA is an attractive option for local administration as the risk for systemic effects in case of leakage from the local compartment will be minimal due to a rapid clearance by the liver. Conversely, IL4–10 FP highSA might be suitable for systemic therapy since it provides improvements compared to stand-alone IL-10 and IL-4 such as a longer serum half-life and synergistic therapeutic effects. Future studies are warranted to evaluate the clinical potential of either molecule.IL-4 and IL-10 are potent anti-inflammatory cytokines that in preclinical studies yielded promising results ,27. Yet


Introduction: Hepatic granulomas are common in patients with sarcoidosis, but clinically significant liver disease is uncommon and poorly studied. We aimed to characterize the frequency and clinical course of hepatic sarcoidosis in an ethnically diverse population.Methods: This is a retrospective study including all cases of hepatic sarcoidosis in a single center. The median follow-up time was 49 months (4–121). Cases were identified based on ICD-9 and ICD-10 codes for granulomatous hepatitis, sarcoidosis, and hepatic sarcoidosis. The Chi-square and Wilcoxon-signed rank tests were used as indicated to assess for differences between groups.Results: Of 286 patients with sarcoidosis, 27 had hepatic involvement; 78% were female and 48% African American. The most common pattern of liver tests abnormalities was cholestatic. Ten patients had clinically significant hepatic involvement: cirrhosis in seven (25.9%), portal hypertension in nine (33%), and portal vein thrombosis in one (3.7%). Sex, race, and ethnicity were not associated with an increased risk of hepatic involvement or symptomatic hepatic sarcoidosis. Most patients received medical treatment, most commonly oral glucocorticoids. At the end of the follow-up period, all patients were alive but two had undergone liver transplantation due to complications of hepatic sarcoidosis. Three patients with hepatic sarcoidosis had initially been classified as AMA-negative PBC.Conclusions: Hepatic sarcoidosis was found in 9.4% of patients with sarcoidosis and was clinically significant in 37% of those. Identifying and monitoring hepatic sarcoidosis is crucial given its potential complications. Sarcoidosis is a systemic granulomatous disease of unknown etiology characterized by the presence of non-caseating granulomas in affected organs . AlthougMost patients with hepatic sarcoidosis have mild biochemical abnormalities including an elevated alkaline phosphatase (ALP) and gamma glutamyl transpeptidase (GGT) –8. LiverClinical manifestations of hepatic sarcoidosis vary from asymptomatic disease to severe complications due to cirrhosis and/or portal hypertension. The natural history of hepatic sarcoidosis is poorly understood, with important differences reported across diverse racial and ethnic backgrounds. Hepatic involvement is reportedly more frequent and more severe among African Americans. The aim of this study was to describe the frequency of hepatic sarcoidosis and its clinical course in an ethnically diverse population in a single center in the Southeast of the United States and to identify predictors of prognosis among patients with hepatic sarcoidosis.We aimed to identify patients with sarcoidosis and patients with granulomatous hepatitis of all causes. Patients were identified through ICD-9 and ICD-10 codes D86.9 , D86.8 (sarcoidosis of other sites), and K75.3 (granulomatous hepatitis), seen between January 1st, 2010 and December 1st, 2016 at the University of Miami/Jackson Memorial Hospital. After a manual chart review, patients older than 18 years of age with a diagnosis of sarcoidosis or granulomatous hepatitis were included in the study. In addition, those with granulomatous hepatitis were categorized according to etiology, as follows: autoimmune disorders, systemic infections, malignancies, drug-induced, or idiopathic causes.Patients diagnosed with sarcoidosis were further evaluated for hepatic involvement. To confirm the diagnosis of hepatic sarcoidosis, we collected data on the hepatic lesions seen in imaging studies, characteristics of the liver granulomas in biopsies, clinical and/or laboratory evidence of liver involvement, and extra-hepatic manifestations of systemic sarcoidosis. For the purpose of this study, hepatic sarcoidosis was defined as “definitive” if biopsy-proven, and “suspected” when the clinical history and objective laboratory data suggested sarcoidosis and no alternative diagnosis existed.Due to the clinical and histological similarities between primary biliary cholangitis (PBC) and hepatic sarcoidosis, we also retrieved a list of patients with ICD-9 code K74.3 (PBC) in an effort to identify cases of hepatic sarcoidosis potentially misdiagnosed as anti-mitochondrial antibody (AMA)-negative PBC .Data on demographic characteristics, comorbid conditions, extrahepatic manifestations of hepatic sarcoidosis, liver biochemical tests at baseline and at last follow-up, treatment, and clinical outcomes were collected. For patients with AMA-negative PBC, additional information on associated co-morbidities  and bile duct abnormalities on histology were also collected.t-test or Wilcoxon signed rank test. A two-sided p-value < 0.05 was considered statistically significant. Analyses were performed using IBM SPSS Statistics V25.0 .Descriptive statistics were used to summarize the cohort demographics. When appropriate, categorical variables were analyzed using chi-square or Fisher's exact test, and continuous variables using Student n = 326).A total of 632 medical records were identified as having a diagnosis of sarcoidosis and/or granulomatous hepatitis by ICD code. Of those, 286 had confirmed sarcoidosis, 163 AMA-positive PBC, 20 AMA-negative PBC, 3 idiopathic granulomas, 1 tuberculosis, and 159 had insufficient information or incorrect diagnosis, with lack of granulomas, sarcoidosis or PBC . PatientOf the 286 patients with sarcoidosis, 198 (69%) were female, 145 (51%) Caucasian, 122 (43%) African Americans, and 63 (22%) Hispanics. Only 27 had hepatic involvement: 18 with a definitive diagnosis based on biopsy findings and nine with a suspected diagnosis: six were diagnosed based on medical history and three were initially misdiagnosed with AMA-negative PBC which was later modified to hepatic sarcoidosis. Median time from sarcoidosis diagnosis to determination of hepatic involvement was 5.7 months . Median duration of follow-up from diagnosis of hepatic sarcoidosis to last visit was 4.0 years .In our cohort of 27 patients, 20 were female (74%), 13 were African American (48%), 10 were Caucasian (37%) and 4 (15%) were Hispanics. The median age at diagnosis of hepatic sarcoidosis was 45.7 years (range: 23.9–72.5 years). Laboratory tests at baseline and follow-up are illustrated in The most common laboratory abnormality was an elevation in serum ALP, or a cholestatic pattern of liver enzyme abnormalities. Median serum ALP at baseline was 3.5 times the upper limit of normal, associated with minimal elevation in transaminases . Anti-nuAt presentation, the most frequently reported symptom was fatigue, followed by pruritus, weight loss, and hepatomegaly equally . Ten patp = 0.29, 1.0, and 0.62 compared to no treatment 0.29). Antimetabolites elicited a statistically significant change in ALP in individuals with preexisting ALP elevation (p < 0.05). On the other hand, patients receiving oral glucocorticoids or biologic agents showed some lowering in their ALP level which was not statistically significant, p = 0.09, 0.11, respectively.A total of 21 patients were medically treated with one or more agents during our follow-up period; six patients were never treated medically. Oral glucocorticoids were the most frequently used in 17 patients (63%), followed by antimetabolites in 15 patients (56%), and biologic agents in five patients (19%). Median change in ALP from baseline to last follow-up for patients treated with anti-metabolites, steroids, and biologics was −163.5, −219, and −108, respectively, compared to −162.5 in untreated patients  due to complications of hepatic sarcoidosis. The first is a 56-year-old African American woman with well-established cutaneous and pulmonary sarcoidosis, hypertension, hyperlipidemia, depression, and Parkinson's disorder, who initially presented with complications of cirrhosis including esophageal varices, encephalopathy, and hepatopulmonary syndrome. Although the treating physician was concerned about AMA-negative PBC, her explant showed cirrhosis with moderate chronic inflammation, ductopenia, intracellular cholestasis, with multiple portal and lobular non-necrotizing granulomas. There was no evidence of destructive cholangitis. Non-necrotizing granulomas involving the fibroadipose tissue surrounding hilar vessels were noted. Her post-operative course was complicated by delayed graft function, two embolic strokes, and wound infection, but she eventually recovered.The second patient is a 65-year-old Caucasian male with a long-standing 20-year history of extensive granulomatous liver disease which eventually led to end-stage liver disease. He had been treated with ursodiol, multiple courses of steroids and methotrexate without success; he underwent OLT due to complications of portal hypertension. His explant showed a cirrhotic liver with marked cholestasis, ductopenia, focal periductal fibrosis, mild chronic inflammatory infiltrates, and non-caseating granulomatous inflammation. The post-operative course was remarkable for partial wound dehiscence, an episode of cholangitis, and acute cellular rejection.p = 0.66, 0.79, 0.15, respectively). In our cohort there was no statistically significant association between sex (p = 0.49) or race (p = 0.86) and clinically significant hepatic sarcoidosis.Sex, race, and ethnicity were not associated with an increased risk of hepatic involvement in patients with systemic sarcoidosis ; in addition, both can coexist with sarcoidosis , 21. In In conclusion, our study highlights the importance of correctly identifying hepatic sarcoidosis, given increased morbidity when associated with cirrhosis and/or portal hypertension. Race, sex, and ethnicity may not predict hepatic involvement and disease progression. When appropriate, special attention should be given to AMA-negative PBC patients to exclude the possibility of hepatic sarcoidosis.The raw data supporting the conclusions of this manuscript will be made available by the authors, without undue reservation, to any qualified researcher.The studies involving human participants were reviewed and approved by University of Miami Institutional Review Board. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.CL designed the study concept. Data collection was performed by NF, PS, and LD. Analysis and interpretation of data was performed by MS and CL. Draft of the manuscript was performed by NF and MS. MG-B, MM, and CL provided the critical revision of the manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


N, N-dimethylacetamide (DMAc); N, N-dimethylformamide (DMF); and N-methyl-2-pyrrolidinone (NMP). A set of concentrations of highly stable surfactant-free graphene nanofluids developed in-house was prepared and characterized. A correlation between the modification of the vibrational spectra of the fluids and an increase in their thermal conductivity in the presence of graphene was confirmed. Furthermore, an explanation of the non-modification of the thermal conductivity in graphene-NMP nanofluids is given based on its structure and a peculiar arrangement of the fluid.It is well known that by dispersing nanoparticles in a fluid, the thermal conductivity of the resulting nanofluid tends to increase with the concentration of nanoparticles. However, it is not clear what the mechanism behind this phenomenon is. Raman spectroscopy is a characterization technique connecting the molecular and macroscopic world, and therefore, it can unravel the puzzling effect exerted by the nanomaterial on the fluid. In this work, we report on a comparative study on the thermal conductivity, vibrational spectra and viscosity of graphene nanofluids based on three different amides:  However, as dimension decreases, the effective thermal conductivity  conduction towards the cold edges of the solid piece or to a second piece  and then, by (2) forced convection in air or liquid. It is clear that the material, together with the structural and architectural design of heat sink, is crucial to increase efficiency levels of active cooling systems. Great efforts have been made to improve the performance of current heat sinks, such as the modification of the architectural designs ,9,10,11,Among these active methods, the air-based (heat-sink-and-fan) can be found in many electronic devices from the cheapest laptop to the most expensive laboratory equipment. However, this is an old technology and not always efficient. Furthermore, it is not cost-effective for the dissipation of large amounts of heat. Murshed and Nieto de Castro  demonstrIn this context, liquid-cooling technology has proven to be an efficient and low-cost method to cool high-power components ,15,16, dWithin liquid-based active cooling, the most common is the use of heat transfer fluids (or coolants) confined in basins. The coolant flows from tower pumps through pipes along the hot side of the device, thereby reducing the temperature.Conventional coolants are mainly classified into dielectric and non-dielectric fluids. Dielectric coolants are organic-based fluids with quite low thermal conductivity but widely used in direct liquid immersion systems, while, the non-dielectric coolants are preferred for heat pipes and microfluidics due to their superior thermal properties compared to their dielectric counterparts. They are normally aqueous solutions and thus exhibit quite a high heat capacity and low viscosity. Water, ethylene glycol, and mixtures of these two are the most popular and widely used as coolants for many electronic devices . HoweverNanofluids (NFs) are colloidal dispersions of nanoparticles (1–100 nm) suspended in a base liquid . The prei) Increase of the thermal transfer due to Brownian motion of nanoparticles, (ii) localized convection created in the fluid due to Brownian motion of nanoparticles, (iii) agglomeration of nanoparticles, (iv) enhanced thermal energy transfer due to increased interatomic interactions arising from the modification of interatomic potential, (v) ordered layering of liquid around the solid, and (vi) ballistic phonon transport of heat through solid nanoparticles [i), (ii) and (iii) cannot explain our experimental observations. In addition, the displacement of some Raman modes of DMF-graphene NFs led us to conclude that there is a strong modification of the interatomic potential as a function of graphene concentration, as the model (iv) suggests.Several studies have been reported on the enhancement of thermophysical properties in nanofluids, however, the mechanism behind this phenomenon is not clear ,47,48,49articles ,47,48,49articles , we showTaking into account all of the above, in this paper, we report an extension of our previous work related to the enhancement of thermophysical properties of graphene-based nanofluids . Here, wN, N-dimethylacetamide , N, N-dimethylformamide  and N-methyl-2-pyrrolidinone  were used as the base fluids. The preparation of the nanofluids consisted of direct mixing of the base fluid with graphene nanosheets. Then, graphene was dispersed in the fluid using a planetary ball mill  and soft ultrasonic vibration  for 1 hour. These techniques were used to suppress the formation of particle clusters in order to obtain stable dispersions [Graphene flakes were prepared from graphite  by mechanical exfoliation. An extended description of the sample preparation can be found in the section on experimental methods in the supporting information of Reference . The propersions . The sampersions .T = 20–21 °C. The shear rate used was 2880 s−1 with a measurement time of 30 seconds. The Raman spectra were recorded by T64000 Raman spectrometer manufactured by HORIBA Jobin Yvon . It was used in single grating mode (2400 lines) with a spectral resolution better than 0.4 cm−1. The NF was placed in a transparent quartz cuvette. Then a green diode laser (λ = 532 nm) was focused on the cuvette by using a 50× long working distance microscope objective. The power of the laser was kept as low as possible (<2 mW) to avoid any possible effect from self-heating. Raman analyses of the samples were repeated under similar conditions as a function of time  to verify the reproducibility of the Raman spectra  method ,52 in thN, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc) and N-methyl-2-pyrrolidinone (NMP). Progressive enhancement of k was observed in DMAc and DMF-based nanofluids (NFs) as C increased, with a maximum enhancement of ~48% for C = 1.50 mg/mL in DMAc-based NF. Concentrations between 0.1–0.5 mg/mL in DMF and DMAc produced relatively large enhancements of ~6–25% and 3–17%, respectively. While in the same set of concentrations no significant enhancement of k was detected in NMP-based NFs. In contrast, in the case of viscosity, a maximum enhancement of ~44% was observed for 0.50 mg/mL graphene in NMP.The An increase in viscosity as the nanoparticle concentrations rise has been frequently observed in graphene-based ,57,58,59C = 0, 0.05 and 0.10 mg/mL. The vibrational assignment was carried out based on the work of Peek and McDermott [Firstly, we will discuss the Raman characterization of DMAc and DMF as a function of graphene concentration ranging from 0 < C < 1.5 and 0 < C < 1.13 mg/mL, respectively. Due to the very high light absorption of the most concentrated dispersions , we were only able to detect one peak in the entire Raman spectrum. The vibrational assignment for DMAc and DMF was done based on the work of Chalapathi and Ramiah . SecondlcDermott  and Xu ecDermott . The peacDermott .−1 for a band around ~470 cm−1 (see 3–N–CH3) of the DMAc molecule [The Raman spectra of DMAc for different graphene concentrations are displayed in cm−1 see b. This bmolecule . The dis−1 occurred for a rocking vibration of the bond (CH3)–N of the DMF molecule. In a previous study, we related such observation to an apparent hardening of the bonds of DMF molecules produced by the presence of the graphene flakes. [A similar effect can also be observed in DMF-based nanofluids as displayed in  flakes.  In this p-orbital with unshared electron pairs  along the out-of-plane direction [p-orbitals. It can favor a π-π bond between the solvent molecules and the graphene surface. This interaction thus increases the rigidity of the internal bonds of the molecules closest to graphene and, consequently, modifies their Raman spectra. It is important to mention that our simulations suggested that this interaction is local rather than global, i.e., just the molecules around of graphene flakes feel this change. It is not clear how the rest of the fluid is also affected by this interaction. Returning to DMAc NFs, a similar blue-shift in several Raman modes can be observed. If we consider that DMF and DMAc molecules are amides with quite similar structures and electron delocalization, then it is reasonable to suggest that a similar geometric configuration occurs in DMAc-based NFs. As a consequence, DMAc molecules may also tend to lay parallel to the graphene flakes, favoring a π-π stacking between the graphene and the molecules thereby contributing to the blue-shift in the Raman spectra.Taking into account that both graphene and DMF molecules contain a irection ,64. The C = 0, 0.05 and 0.10 mg/mL. At first glance, a very small displacement of certain Raman modes can be detected (see −1) and the error determination of each peak position. In conclusion, there is not a significant displacement of the Raman bands as the graphene concentration increases.The case of NMP-based fluids is quite different, cted see . HoweverN-methyl-2-pyrrolidone is a five-membered cyclic amide (with a ring structure), and therefore, the bonds tend to be more rigid than those of amides having a linear structure. Consequently, it is conceivable that small amounts of graphene do not affect or modify the intramolecular vibrations of inner bonds in the solvent. Furthermore, Adams et al. [2 hybridization of N-C-O , can explain the long-term dispersion stability of graphene in NMP. However, the internal structure of NMP seems to be an obstacle to the improvement of the thermal properties of the fluid induced, in other cases, by graphene.The Raman spectroscopy results from graphene-NMP NFs are not surprising if we consider the structure of the organic compound. s et al.  suggestes et al.  reportedAt this stage, one could consider as a possibility that higher concentrations of graphene may be preferable in order to observe a modification of the Raman spectra of NMP. However, although we prepared higher concentrations of this nanofluid, it was not possible to measure their Raman spectra. In addition to the high light absorption in the most concentrated samples, we also observed photoluminescence, which masks the Raman peaks. The origin of this photoluminescence has been attributed to the sonochemical degradation of the NMP suffered during the preparation of the NFs. Previous investigations ,68 have In this work, a correlation between the modification of the vibrational spectra of the fluids, and the increase of their thermal conductivity and viscosity in the presence of graphene is presented, where the base fluids were DMAc, DMF, and NMP. Our results suggest that the presence of graphene produces important changes at the macroscopic level in DMF and DMAc-based fluids. This is reflected in the displacement of some Raman bands when the concentration of graphene increases. The blue-shift of several Raman bands in DMF and DMAc reveals a hardening of the bonds associated with those vibrational modes (intramolecular interactions), which requires higher energy to make them vibrate. In a way, it can be explained as if graphene has the ability to modify, as an external force, the solvent–solvent interaction, and fluid molecules, in turn, influence the intramolecular bonds of the neighbor molecules. This interpretation suggests that there is a strong modification in the intermolecular interaction between fluid molecules in the presence of graphene flakes, which in turn seems to be directly connected with the enhancement of the thermal conductivity of the fluid. In the case of NMP-graphene-based nanofluid no significant modification in the thermal conductivity was found. Similarly, we did not find an important modification in their Raman spectra either. The structure of the NMP molecule and the peculiar arrangement of the bare fluid (dimerization and inner order), can explain why the presence of graphene does not affect NMP in vibrational terms. NMP is a cyclic amide and has a strong tendency to form dimers in the liquid state, therefore, the modification of the intramolecular forces in the cycle would require great efforts. We can deduce from Raman spectroscopy and thermal conductivity results, that those concentrations of graphene are insufficient to impact on the fluid’s thermal properties. We tested a higher concentration of graphene in NMP (C = 0.5 mg/mL), but the thermal conductivity was not enhanced, and the Raman spectrum showed photoluminescence, which masks the Raman peaks. Photoluminescence can be attributed to the degradation of NMP during sonication, which is a crucial step in the preparation of stable dispersions. The sonochemical degradation of NMP, together with the formation of the small organic contaminating particulates, affects the interaction between the graphene flakes, which could also contribute to a detrimental impact on the thermal conductivity.


RGO/SnO Nitrogen dioxide NO, a well-Metal oxide gas sensors have been extensively studied and commercially applied. As an n-type semiconducting metal oxide material , tin oxive films . Meanwhietection ,5,6,7.In recent years, graphene and its derivatives (such as graphene oxide (GO) and reduced graphene oxide (RGO) etc.) have shown great potential in chemical- and bio-sensors because of their low cost, high specific surface area, low electrical noise and high carrier mobility at room temperature ,5. To fu studies ,8,9,10.The metal oxide/graphene composite materials were prepared by many methods such as the gas–liquid interfacial solvothermal method , the hydIn this paper, different amount of SnORGO aqueous dispersion  was purchased from Chengdu Organic Chemicals Co. Ltd., Chinese Academy of Sciences . SnOThe morphologies of the as-prepared sensitive films were observed by a Hitachi S4800 field emission scanning electron microscope  operated at an acceleration voltage of 20 kV. The microstructures were characterized on a FEI Tecnai G2 F20 transmission electron microscope  equipped with energy dispersive X-ray (EDX) spectrometry at an acceleration voltage of 200 kV. The phase composition was identified by grazing incidence X-ray diffraction (XRD) technique on a Panalytical X’Pert Pro MPD diffractometer  with Cu KR) of the sensors were obtained by Keithley 2700 multimeter/Data Acquisition System at a constant flow rate of 100 mL/min, when NOThe testing apparatus for gas sensing is shown in In this paper, sensing response is defined asWhen the resistance of sensor changes from the initial value to 90% of the total resistance change during the adsorption process, the corresponding time is response time. While the recovery time is the time that the resistance of sensor recovers 90% of the total resistance change during the desorption process .The SEM images in The pure RGO film shown in After introducing SnOarticles  but alsoRaman spectra are commonly used to characterize graphene-based materials. The Raman spectra of the RGO film and the RGO/SnOnch mode ,9,10. Thd to SnO2. Both chRaman aterials ,10. ID/IThe FTIR spectra of RGO and RGO/SnOfrom SnO2,13,14, wolecules ,13, and As a matter of fact, more active adsorption sites means a more difficult desorption of NOne drift .Therefore, the 5.1%RGO/SnOto 101 s , the resRous work , the FirCompared with the previously reported sensors based on RGO/ SnO hybrids ,15,17 as sensors ,17 have A room temperature chemoresistive NO