Vibrational spectroscopy studies of interdiffusion in polymer laminates and diffusion of water into polymer membranes.

Confocal Raman microspectroscopy has been used to study the interdiffusion in polymer laminates at the interfacial region between the constituent polymer layers. The effects of the polymer molecular weight, annealing temperature, and annealing time have been studied. Three different laminates with various PMMA molecular weights have been examined, with a view to studying the hydrogen bonding interaction between the alcohol and ester groups of PVOH and PMMA layers. It has been found that v(C=O) band shows no apparent frequency shift due to hydrogen bonding. However, considerable broadening of the v(C=O) band has been observed at the interfacial region. In order to study the effect of annealing temperature, a PAN/PVOH laminate has been chosen. It has been shown that the degree of hydrogen bonding is reduced if the polymer laminate is annealed at a higher temperature than the glass transition temperature of both of the constituent polymers. No significant change has been observed after annealing the laminate for various lengths of time. It has been shown that Raman imaging and Raman microscopy can provide invaluable information about the molecular distribution and chemical interactions of various phases in polymer blends. The diffusion of pure water and also water from some ionic solutions into sulphonated polyetherethersulphone/polyethersulphone, SPEES/PES has been studied using Fourier transform infrared-attenuated total reflectance, FTIR-ATR spectroscopy. The effects of sulphonation level, annealing temperature, ionic concentration, and presence of some ionic species on diffusion of water into SPEES/PES has been examined. In addition the sorption and desorption processes, and diffusion into a laminate of SPEES/PES-PVOH has also been studied. It was found that the above diffusion processes are not Fickian nor Case II and is best described by a dual-mode sorption model.The diffusion coefficient for H2O in various cationic solutions into SPEES/PES has a descending order of Li[+] > Cs[+] > Na[+] > K[+]. Increasing the ionic concentration results in a decrease in the water diffusion coefficient. It was found that an increase in annealing temperature caused the diffusion curve to become more sigmoidal in shape with a decreases in diffusion coefficient

Vibrational spectroscopy studies of interdiffusion in polymer laminates and diffusion of water into polymer membranes

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FTIR-ATR studies of diffusion and perturbation of water in polyelectrolyte thin films. Part 4. Diffusion, perturbation and swelling processes for ionic solutions in SPEES/PES membranes

We report diffusion rates and equilibrium concentrations of water in a polyelectrolyte SPEES/PES film using ATR/FTIR spectroscopy. The data for water obtained by fitting spectral intensities to a dual mode diffusion model in the presence of different counter ions (at 0.2 mol dm(-3)) follow the order Li+ > Cs+ > Na+ > Ca2+ > K+. Diffusion is progressively slower for higher concentrations of NaCl (0.2-0.85 mol dm(-3)) and the NO3- counter anion leads to a faster diffusion rate than for Cl- at the same concentration. Both water uptake and diffusion rates are broadly consistent with expectations based on the differential degrees of swelling, caused by changes in the SO3-/SO3- interpolymer chain repulsive forces leading to a decrease in volume diffusion compared with the value for pure water. Direct spectral measurements of the degree of swelling confirm that the process does occur, although the order of the swelling amounts does not map directly onto that of the diffusion rates. This is probably because the interfacial dissociation processes are hydration dependent. (C) 2002 Elsevier Science Ltd. All rights reserved

ATR-FTIR study of the diffusion and interaction of water and electrolyte solutions in polymeric membranes

We present a comparative review of the most up to date ATR-FTIR measurements of water diffusion into three polymers, PET, PVC and SPEES-PES. New data on the diffusion of water from electrolyte solutions into SPEES-PES have been added and we discuss reasons for changes in transport coefficient due to ionic screening of interchain repulsions. Finally, we point out, and attempt to interpret, the differences in perturbation of the water IR bands in the three different polymer types. Some suggestions for further elucidation of the effect have been made