Bending-cantilever method for the study of moisture swelling in polymers

Self-induced bending of a bilayer strip is shown to be a simple but sensitive method for the study of water absorption and swelling in polymers. Expressions for both the time-dependent and equilibrium curvature of the strip have been derived, enabling both diffusional and dilatational parameters to be extracted from experimental data. To illustrate the technique, it is shown that a vacuum-dried epoxy swells linearly with water content, at a rate of 0.93% in volume per weight percent of water. Desorption into vacuum has been observed under diffusion-controlled conditions and the diffusion coefficient for water in the epoxy found to be 2.5×10
⁻⁹
cm
²
/s at 295 K.