No abstract

Diffusion coefficients for the moving boundary thermosensitive poly(N‐isopropylacrylamide) hydrogels, which were swelled to equilibrium in aqueous solutions of either BSA or phenol, have been determined. Using a uniaxial compression apparatus the collective (Dcol) and with confocal Raman spectroscopy the mutual (Dmut) diffusion coefficients were estimated. The solute distribution in the hydrogel in addition to the effect of the swelling ratio, the cross‐linking ratio and the hydrogel cylinder thickness on the Young's modulus were investigated.

Thin, defect-free palladium, palladium/copper and palladium/silver hydrogen absorbing membranes were microfabricated. A dual sputtering technique was used to deposit the palladium alloy membranes of only 1 lm thickness on a nonporous silicon substrate. Advanced silicon etching (ASE) was applied on the backside to create a mechanically stable support structure for the thin films. Performance evaluation was carried out for different gases in a temperature range of 20°C to 298°C at a constant differential pressure of 110 kPa at the two sides of the membrane. The composite membranes show an excellent permeation rate of hydrogen, which appears to be 0.05 Pa m 3 s -1 and 0.01 · 10 -3 Pa m 3 s -1 at 20°C for the microfabricated 23 % silver and the 53 % copper composite membranes, respectively. The selectivity to hydrogen over a gas mixture containing, in addition to hydrogen, carbon monoxide, carbon dioxide and nitrogen was measured. The mass spectrometer did not detect any CO 2 or CO, showing that the membrane is completely hydrogen selective. The microfabricated membranes exhibit both high mechanical strength (they easily withstand pressures up to 4 bar) and high thermal stability (up to 650°C).

A hydrogel kept at its equilibrium swelling state during taking the measurements controlled in a diffusion cell. The diffusion data gained from Raman spectra were analyzed to calculate the mutual diffusion coefficient in the hydrogel as semi-infinite medium. The relation between the solute concentration and Raman intensity for poly(N-isopropylacrylamide), which is characterized by the distinct peak for the isopropyl group at 2925 cm-1 was taken into account. The determination of the mutual diffusion coefficient, Dmut for hydrogels/phenol system was achieved successfully using confocal Raman spectroscopy at different solute concentrations. At 25oC, the value of the mutual diffusion coefficient is found between 5.61845x10-11 m2/s and 3.34565x10-9 m2/s for the hydrogel loaded with phenol of an initial concentration of 0.01 mM and 0.1 mM, respectively.