| Abstract: | A complex mechanism characterizes the water uptake kinetics in hydrogels, as a consequence of the strong structural changes occurring in the material during the sorption process. Water acts as a plasticizer, reducing the glass transition temperature of the polymer below the sorption temperature and determining a glass transition in the polymer. In this study the changes in the ultrasonic attenuation and velocity in semicrystalline Poly-vinyl-alcohol (PVA) hydrogel films during water sorption are measured by a pulse-echo system. The ultrasonic wave propagation is applied to monitor the position of the swollen/unswollen fronts and to the measurement of velocity and attenuation. The structural changes in PVA hydrogels, monitored by Wide Angle X-ray Diffractometry (WAXD), performed during the sorption process, are correlated with the ultrasonic data. |
