Abstract
Brillouin light-scattering measurements of H2O imbibed in hydrogels of poly(2-hydroxyethyl methacrylate) of two cross-linking densities have been made at 294 K. Increase in the amount of water imbibed in 19-30 Angstrom size pores of the cross-linked network causes the velocity of sound to decrease monotonically from a value, which differs for the two pure polymers, to a limiting value for pure water. The absorption coefficient reaches a maximum at about 30% water content and then decreases toward that for pure water. The velocity and absorption coefficient of both pure polymer and hydrogel containing 32% water were measured from 110 to 300 K. The former decreases and the latter increases with increasing temperature, and both show a change in the slope at about 160 K for the hydrogel, which agrees with the calorimetric glass transition temperature of the hydrogel. The effect of the water on the velocity and absorption coefficient of the polymer increases with temperature.