Molecular mobility and transport in polymer membranes and polyelectrolyte multilayers

Polyelectrolyte multilayers prepared by the layer-by-layer technique provide an efficient way to generate planar structures of tailored surface charge and hydrophobicity, which are used as membranes for pervaporation. The use of polyelectrolyte multilayers to form the membrane permits tailoring the surface charge of the membrane and, thus, selectivity; at the same time, it reduces fouling of the membrane by adsorption of organic matter. Pulsed field gradient (PFG) nuclear magnetic resonance has been used to investigate the diffusion of probe molecules into polymer systems. Evaluation of the apparent diffusion coefficient in porous poly(amide) results in a pore size of 4 microm, as found in electron micrographs. For the pore size obtained for polyelectrolyte multilayers, no equivalent pores could be found in microscopy. Propagators for the diffusion of propanol and propanol-water mixture into multilayers reveal that there might be selective interaction of probe molecules with the polyelectrolyte system.     

Sorption of cadmium ions from aqueous solutions onto nanoporous modified carbon sorbents

Physicochemical properties of nanoporous modified carbon sorbents and sorption of cadmium ions (0.1–20 mg L^?1) onto them from nitrate solutions at pH 5–7 were studied. The acid-base nature of functional oxygen-containing groups on the carbon surface of the sorbents was determined. The ability to sorb cadmium ions depends on the kind of chemical modification of the sorbent surface.     

Combustion of a Powder Layer of Methane Hydrate: The Influence of Layer Height and Air Velocity Above the Layer

The paper studies the dissociation and combustion of a layer of methane hydrate powder at a forced air flow over the upper surface of the layer (the air velocity is directed parallel to the upper surface of the layer). The influence of the layer thickness and air velocity on the combustion of gas hydrate is investigated. The calculated curves for the effect of the heat transfer coefficient, external convection and vapor concentration on the combustion temperature are obtained. The layer thickness and the air velocity significantly affect the dissociation rate of methane hydrate.

     

STRUCTURE,MORPHOLOGY, AND COMPOSITION OF NATURAL GAS HYDRATES SAMPLED IN THE KEDR-1 MUD VOLCANO (LAKE BAIKAL)

Journal of Structural Chemistry - Structure, morphology, and composition of the gas for natural gas hydrates sampled in the Kedr-1 mud volcano (Lake Baikal) are studied. It is shown that all these...     

Pore size distribution measurements in small samples and with nanoliter volume resolution by NMR cryoporometry

NMR cryoporometry is demonstrated to provide access to pore size and pore size distribution in small amounts of porous materials. With a conventional NMR spectrometer and probe, the detection limit for total pore volume is shown to be on the order of 100 nL with a volume resolution on the order of a few nanoliters.     

Self-diffusion and nuclear magnetic relaxation of dendritic macromolecules in solutions

The self-diffusion and nuclear magnetic relaxation of poly(butylcarbosilane) and poly(allylcarbosilane) dendrimers dissolved in deuterated chloroform and poly(amidoamine) dendrimers with hydroxyl surface groups in solutions with methanol have been studied. The diffusion rates(D) have been measured by the pulsed-field-gradient nuclear magnetic resonance. It is shown that experimental concentration dependencesD(ϕ) obtained for macromolecules in the dendrimer-solvent systems studied can be reduced to a unified view, and thus, the generalized concentration dependence of the normalized diffusion rates of dendrimers can be obtained. In the macromolecular volume concentration range from 0.01 up to 0.55, the generalized dependence of the normalized diffusion rates for dendrimers coincides with the analogous dependence for globular proteins in aqueous solutions; the last result suggests that self-diffusion features of dendrimers and globular proteins are in general similar. It is also shown that the experimental data obtained permit one to characterize the changes of the own monomer density of dendrimers depending on their molecular weight and, as a consequence, to make a conclusion about the swelling of dendritic macromolecules in the solutions studied.     

Internal magnetic field gradients as information source about porous media characteristics

The geometry of particles is analyzed by the example of a model porous system (filling of glass spheres and glass cylinders) studied by nuclear magnetic resonance. The experimental approach is based on the registration of the <G _int> (ζ) dependences, where <G _int> is the effective (average) internal magnetic field gradient and ζ=<r ²>^1/2<R> is the ratio of the root-mean-square displacement of molecules to the average particle size <R>. It is shown that the dependence <G _int> (ζ) can be approximated by the power law <G _int>(ζ) ∝ ζ^α, where the power index α does not depend on the particle size but is sensitive to its geometry.