Analysis of the water bound to a polymer matrix by infrared spectroscopy

This article focuses on the interaction of water with solid polymers. A por tion of the water adsorbed in hydrophilic materials is strongly bound to in dividual sites (bound water), while an additional amount is bound less firm ly to the polymeric chain (free water). Both free and bound water have been the subject of many studies that have uncovered, in some cases, qualitativ e evidence of the presence of water directly bound. In this article, we rep ort a method to determine the different fractions of water adsorbed in hydr ophilic materials. One fraction corresponds to the first layer in contact w ith the adsorbing solid and the other corresponds to the remaining water ab sorbed layers. We were able to determine said quantification by means of me asuring the change in the natural vibration frequency brought about by the interaction of water molecules with the solid. The measurement was done on films of methylcellulose exposed to humid environments using infrared spect roscopy and gravimetric static microclime sorption methods. Theoretical pre dictions for bound water were developed using multilayer adsorption models. The experimental concentration of bound water as a function of relative hu midity was compared with these predictions, allowing us to judge the applic ability of different adsorption models employed in the study of gas condens ation. (C) 2001 American Institute of Physics.