A STUDY OF THE WATER SORPTION KINETIC OF POLY(HEMA) HYDROGELS BY SLAMAND FT-IR MEASUREMENTS

The relative changes in the ultrasonic attenuation measured by scannin g laser acoustic microscopy (SLAM) during water sorption in Poly-hydro xy-ethil-methacrilate [Poly(HEMA)] are analyzed, Acoustical images per formed at 10 and 30 MHz of Poly(HEMA) during water absorption show an ultrasonic attenuation increase followed by a decrease, This phenomeno n is analyzed in terms of reflections, scattering, and absorption of t he acoustic waves, However, the contribution of scattering and reflect ion may be neglected and the time dependence of acoustic attenuation i s attributed to absorption of the acoustic waves occuring in accordanc e with the glass transition, although induced by a solvent and not by temperature. Fourier transformed infrared spectrometry (FT-IR) measure ments indicate that bound water is responsible of the glass-rubber tra nsition, On the other hand, the longitudinal velocity changes are only affected by the variations of density and mechanical properties of th e polymer during water sorption, The traditional weight gain data are compared with the attenuation changes observed by ultrasonic measureme nts.