ULTRASONIC WAVE ATTENUATION DURING WATER SORPTION IN POLY(2-HYDROXYETHYL METHACRYLATE) HYDROGELS

A scanning laser acoustic microscope (SLAM) was used to measure the ac oustic attenuation during water sorption in a film of crosslinked poly (2-hydroxyethyl methacrylate) [poly(HEMA)] hydrogel. The contribution of reflection, scattering, and absorption of acoustic waves to the mea sured attenuation is evaluated. The analysis of a model accounting onl y for the possible reflection of the acoustic waves at the swollen/uns wollen boundaries indicates that the time dependence of the attenuatio n during water sorption cannot be explained simply by accounting for t he presence of two additional interfaces. A predominant contribution o f acoustic wave absorption during the glass transition, occurring at t he two swollen/unswollen interfaces, is assumed. Also, microvoids cann ot be excluded as contributors to craze growth in the glassy matrix at the penetrant/polymer interface.