FTIR–ATR studies of the sorption and diffusion of acetone/water mixtures in poly(vinyl alcohol)

The diffusion kinetics of water and acetone into dried PVOH polymer films have been measured simultaneously using the FTIR–ATR technique. The data have been fitted to a pseudo-Fickian model, along with allowance for a ‘lag’ time which lengthens considerably when the water mole fraction is low. It has been found that a case II model is viable at short times when the polymer is ‘glassy’ (<Tg). However, as water enters the polymer (unzipping the chain–chain hydrogen bonding), conversion to a ‘gel’ is rapid and the crystallinity drops concurrently. A Fickian-like model then becomes viable at intermediate times. FTIR–ATR is an excellent technique with which to study sorption from solvent mixtures. In this case, for example, we have demonstrated that acetone does not enter a dry polymer film and that the micro-crystallinity of the PVOH returns at longer times. Neither of these two potentially important results could have been obtained using gravimetric methods.