Shape memory of composites based on silicone rubber and polyacrylamide hydrogel

The shape memory of hydrophilic composite materials based on silicone rubber and slightly crosslinked polyacrylamide, which is a non-ionic hydrogel, has been studied. Before the shape memory testing, it was necessary to determine the glass transition temperature (T_g) of the slightly crosslinked polyacrylamide as well as the mechanical properties of the composites at temperatures above T_g of a crosslinked polyacrylamide. Afterwards, the shape memory of the composite material was tested by performing a set of simple experiments based on deformation and heating of test pieces, their subsequent cooling and deformation force removing, and their repeated heating or water swelling, during which the residual elongation was measured and calculated. The composite material shaped in this way resumes its original shape if it is again heated above T_g of the crosslinked polyacrylamide or allowed to swell in distilled water. There exists a limiting concentration of hydrogel phase (approx. 30 phr), which is limited by good dispersion and good contact of hydrogel particles within the silicone matrix, under which the shape memory does not occur, and above which it exists.