Interaction of supercritical CO2 with alkyl-ammonium organoclays: changes in morphology

This paper investigates the influence of supercritical carbon dioxide on the morphology and surface chemistry of three organic modified montmorillonite species. Alkyl based quaternary ammonium surfactants with differing numbers of chains attached, were chosen to vary the degree of CO(2)-philicity exhibited by the organoclay. In a high pressure batch vessel, the different organoclays were suspended in the supercritical solvent at temperatures of 50 and 200 degrees C and pressures of 7.6 and 9.6 MPa and then removed after de-pressurization at 0.2 or 4.8 MPa/s. The structures of these treated clays were characterized by X-ray diffraction (XRD), differential scanning microscopy (DSC), and thermogravimetric analysis (TGA), and their chemical properties were analyzed by various methods including atomic absorption spectroscopy, and water uptake measurement. Solute-solvent interactions plasticized the organic medium while suspended in the supercritical fluid, which resulted in greater chain mobility and further cation exchange. The results indicate that intercalated surfactants exhibiting a paraffin complex arrangement were most likely to experience significant basal expansion, provided the tilt angle was not already close to being perpendicular to the silicate surface. At the lower processing temperature condition, the chemistry of the clay surface was notably altered by the CO(2) associations with the Lewis acid/base sites, which significantly reduced the moisture adsorption capacity of the material. For those organoclays demonstrating basal expansion, it was noted that the resulting particle size was increased due to enhanced porosity.     

Thermal and real-time FTIR spectroscopic analysis of the photopolymerization of diepoxide-vinyl ether mixtures

Both epoxides and vinyl ethers can be polymerized cationically albeit through different intermediates. However, in the case of epoxide-vinyl ether mixtures the exact mechanism of cationically initiated polymerization is unclear. Thus, although vinyl ethers can be used as reactive diluents for epoxides it is uncertain how they would affect their reactivity. Cationic photocuring of diepoxides has many industrial applications. Better understanding of the photopolymerization of epoxy-vinyl ether mixtures can lead to new applications of cationically photocured systems. In this work, photo-DSC and real-time Fourier Transform Infrared Spectroscopy (RT-FTIR) were used to study cationic photopolymerization of diepoxides and vinyl ethers. In the case of mixtures of aromatic epoxides with tri(ethylene glycol) divinyl ether, TEGDVE, photo-DSC measurements revealed a greatly reduced reactivity in comparison to the homopolymerizations and suggested the lack of copolymerization between aromatic epoxides and TEGDVE. On the other hand, for mixtures of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, ECH, with TEGDVE the results indicated high reactivity of the blends. The polymerization mechanism might include copolymerization. To examine this mechanism, mixtures of the ECH with a tri(ethylene glycol) mono-vinyl ether, TEGMVE, were studied by both photo-DSC and RT-FTIR. Principal component analysis (PCA) proved to be an efficient tool in analyzing a large matrix of the spectral data from the polymerization system. PCA was able to provide insight into the reasons for the differences among replicated experiments with the same composition ratio and supported the hypothesis of copolymerization in the ECH/TEGMVE system. Thus, blends of cycloaliphatic epoxides and vinyl ethers seem to have a great potential for applications in high-productivity industrial photopolymerization processes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydroxypropyl guar-borate interactions with tear film mucin and lysozyme

The interactions of hydroxypropyl guar (HPG) with boric acid, lysozyme, and mucin were characterized by rheology, light scattering, electrophoresis, and isothermal titration calorimetry to help understand how HPG interacts with tear film components. Borate binds to guar under pH, temperature, and ionic strength conditions representative of those found in the eye. The HPG-borate complexes behave as anionic polyelectrolytes and thus interact with cationic lysozyme, a major tear film protein, whereas HPG-borate does not appear to bind to mucin, an anionic glycoprotein. The interactions of HPG, borate, lysozyme, and mucin can be explained by two physical interactions: (1) pH-dependent binding of borate to carbohydrates and (2) the electrostatic attraction of oppositely charged macromolecules.     

Extraction of rhodium and iridium with 4-(non-5-yl) pyridine

The extraction of rhodium and iridium with 4-(non-5-yl)pyridine (NP) was investigated. The rate of rhodium extraction increases with increasing concentration of NP and chloride ions. Spectroscopic studies indicate that the extracted species is an ion pair, RhCl^3?₆ 3HNP⁺. Under the conditions of optimum Rh extraction ([Cl^?]=3.7 M, [NP]=0.3 M, [H]=0.08 M), iridium is also extracted by NP with similar efficiency in the form of IrCl^3?₆ 3HNP⁺. The use of hypophosphorous acid to labilize rhodium results in a better extraction of rhodium without significantly changing the extraction of iridium. The efficiency and kinetics of the rhodium extraction improve with increasing chloride concentration. For [Cl^?] ? 3.7 M, [H₃PO₂]=2.5 M, [NP]=0.3 M and Ph ≈ 1.6, 82% of rhodium is extracted in 4 min and 95% in 30 min.