Investigation on solvent casting films of surfactant-encapsulated clusters.
The surfactant-encapsulated cluster (SEC) composed of a hydrophobic dimethyl dioctadecyl ammonium (DODA) shell and an encapsulated hydrophilic polyoxoanion core can form casting films. The structure of the casting film is influenced by evaporation rates of organic solvent. When the casting films are prepared by slow evaporation of chloroform, the alkyl chains are considered to possess a partial interdigitation, and the interdigitated length is 1.6 nm. The casting film structure is characterized by scanning force microscopy (SFM), Fourier transformation infrared (FT-IR), wide-angle X-ray diffraction, and differential scanning calorimetry (DSC).
Crystal structure and replacement reaction of coordinated water molecules of the heteropoly compounds of sandwich-type tungstoarsenates.
Six new heteropoly compounds in the [M4(H2O)2(As2W15O56)2]16- series (M = CuII, MnII, CoII, NiII, ZnII, CdII), previously unknown, were synthesized and characterized by means of IR, UV-vis, CV, 183W NMR, TG-DSC, and elemental analyses. The synthetic method used in preparing this type of heteropoly compounds was different from that in preparing the corresponding tungstophosphates in that the starting materials were transition metal chlorides in 1.5 times the stoichiometric amount and the required pH value is lower than 2. The crystal structure of Na16[Cu4(H2O)2(As2W15O56)2].47H2O was solved in triclinic, P1 symmetry, with a = 12.721(3) A, b = 24.516(5) A, c = 26.450(5) A, alpha = 89.90(3) degrees, beta = 77.32(3) degrees, gamma = 89.96(3)degrees, V = 8048(3) A3, Z = 2, and R = 0.0966. This anion is isostructural with the previously reported [Cu4(H2O)2(P2W15O56)2]16-, having a rhombic tetrameric cluster Cu4O16 sandwiched by two trivacant Dawson-Wells anions [As2W15O56]12-. The range of the bond lengths of the equatorial Cu-O bonds is 1.83-2.05 A, while that of the axial Cu-O bonds is 2.30-2.39 A. The distortion of the Cu4O16 cluster is smaller in the As species than in the P species. Two copper atoms in the Cu4O16 cluster are coordinated by water molecules. The replacement reactions of the coordinated water molecules of this series of heteropoly compounds in aqueous solutions and in selected organic solvents are also reported here for the first time. The results show that [Fe(CN)6]4-, [Fe(CN)6]3-, H2NCH2CH2NH2, etc., can replace the coordinated water to form its characteristic color in aqueous solutions, while in organic solvents the coordinated water molecules are lost, leaving unshared coordination positions that can be occupied by some organic ligands such as pyridine, lactic acid, and acetone to restore the octahedral coordination of M2+. The crystallographic morphologies of this series of heteropolyanions after phase transfer are dependent on different transition metal ions present in the central M4O16 clusters although the anions are isostructural with each other.
The micro-mechanical behaviour of artificially cemented sand particles under compression and shear
The mechanical behaviour of cemented sands at macro-scale has been widely studied in the past, while there is still a lack of laboratory test data for the micro-mechanical response. Therefore, a series of uniaxial compression and tangential shear tests on artificially cemented sand particles have been conducted using a microscope to observe their behaviour. First, the consistency of cemented particles with different cementing agents is discussed. Three breakage modes are proposed according to the images taken using a microscope camera. A new parameter named ‘local roundness at contact’ is introduced to emphasise the effect of contact morphology on sample strength. Moreover, the effect of bond thickness on the mechanical response of cemented particles has been investigated. Finally, the shear strength parameters of artificially cemented sand samples have been determined for two different sample diameters.