Infrared Spectroscopy and X-ray Diffraction Characterization of Dimorphic Crystalline Structures of Polyethylenes with Halogens Placed at Equal Distance along the Backbone.
Polyethylenes with halogens placed on each and every 21st, 15th, or ninth backbone carbon display crystallization patterns enabled by the size of the halogen and by changing crystallization kinetics. The different structures have been identified from X-ray patterns combined with a detailed analysis of the infrared spectra of series containing F, Cl, or Br atoms that were either fast or isothermally crystallized from the melt. Under both crystallization modes, all specimens develop layered crystallites that accommodate 5-9 repeating units along the chain's axis. The size of the halogen and intermolecular staggering to maximize packing symmetry are responsible for striking structural differences observed between the series and between the two modes of crystallization. While the small size of the F atom causes a small perturbation to the crystal lattice and the orthorhombic structure is maintained for all members of the series either fast or isothermally crystallized, each Cl or Br-containing system presents dimorphism. Under fast crystallization, Cl and Br containing samples adopt the all-trans conformation (planar Form I), while in slowly crystallized samples gauche conformers set for bonds of the backbone carbons adjacent to the carbon with the halogen due to a close intermolecular staggering of halogens (herringbone Form II). In both forms the methylene sequence between halogens maintains the all-trans conformation. The structural details are extracted from the analysis of the C-halogen stretching region of the IR spectra, and from adherence to the n-alkane behavior of CH2 rocking, CH2 wagging, and C-C stretching progression modes.
Effect of microplasma treatment on stratum corneum lipid molecule
The stratum corneum is a lipid matrix with embedded corneocytes. This layer protects the body against foreign substances and the outer environment. However, the lipid matrix is permeable to selective molecules and this permeability can be improved by several methods. One of these methods includes microplasma irradiation of the skin. Stearic acid is a model fatty acid from the lipid matrix of stratum corneum. In this study, the interaction between microplasma and stearic acid was investigated. Plasma was generated at a low voltage of about 800 V (0-Vpeak) using a thin dielectric (∼30 μm) as a barrier. The plasma electrode treated the lipids under an argon atmosphere at a frequency of 25 kHz. The results of the microplasma treatment were investigated by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy. The concentrations of C, O and N atoms were determined before and after the microplasma treatment. Also, functional groups of C–C/C–H, C–O, C=O, OH–C=O, N–C=O were identified in the carbon spectra. The structure of stearic acid was evaluated by analysis of CH2, CH3 and C=O bands in the ATR-FTIR spectrum.
Science fairs as learning tool for teaching excellence
Science fairs are usually considered to be a pedagogical and cultural activity that involves the students actively. Gifted students need challenges to further develop their skills while maintaining the motivation level. Science fairs may provide the informal environment that will request and allow these students of excellence to challenge themselves by developing a scientific research project. Despite being well known in different countries, in Portugal first steps are being made on the use and implementation of science fairs as effective pedagogical tool. In this work, we will present a 4 years study that was developed on a Portuguese school with the main goal of evaluating the advantages of this informal way of teaching. The study includes an analysis of the evolution of the students’ knowledge that have participated, or visited, the different science fairs. Some advices for the implementation of these projects will be given. The motivation of the students was monitored as well as the knowledge and skills effectively improved by this activity.