MEASURING WATER DIFFUSION IN POLYMER-FILMS ON THE SUBSTRATE BY INTERNAL-REFLECTION FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

Among the various analysis modes which can be used in FTIR spectroscop y, the internal reflection mode enables us to gain near-surface inform ation on solids or liquids. The interaction between the evanescent fie ld created upon internal reflection of the infrared beam and a sample can be. used to monitor the uptake of water molecules by a polymeric f ilm. In this technique, a polymer film of sufficient thickness is appl ied to a substrate and a special cell is used to study the water diffu sion in the polymer films. Spectra were taken automatically at specifi ed time intervals without disturbing either the specimen or the instru ment. Results for polystyrene and poly(methyl methacrylate) films appl ied to a ZnS substrate are presented to demonstrate the method. The di ffusion coefficients of water in these polymers are calculated using t he sorption kinetics approach, and the diffusion process in each type of polymer is discussed. The effects of the molecular weight and defec ts in the films on water transport in the polymers are illustrated. (C ) 1997 John Wiley & Sons, Inc.