Shape memory of composites based on silicone rubber and polyacrylamide hydrogel

Abstract

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 (Tg) of the slightly crosslinked polyacrylamide as well as the mechanical properties of the composites at temperatures above Tg 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 Tg 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.

Novel Shape‐Memory Polymer with Two Transition Temperatures

“…Polymers designed to exhibit a shape‐memory effect require two components on a molecular level, crosslinks to determine the permanent shape and switching segments with a T trans in order to fix the temporary shape 1. Up to now, almost all papers on shape‐memory polymers have introduced switching segments using a covalent linking method 3–10. Only a few reports have detailed the use of non‐covalent interactions 2,11–13.…”

Sequential interpenetrating polymer networks of poly(2‐hydroxyethyl methacrylate) and polydimethylsiloxane

“…Although many reports can be found in the literature dealing with silicone/hydrogel composites and hydrogel‐grafted silicones, 10–27 interpenetrating polymer network systems made from hydrogels and silicone rubber have received relatively little attention 28–31…”

Hydrophilisation of silicone rubber for medical applications

“…The cyclic monomers were polymerised by bulk anionic polymerisation58 using a dispersion of KOH in octamethylcyclotetrasiloxane at 150 °C. Viscosity‐average molecular mass of the product was 560 000 g mol −1 the concentrations of water and ethyl alcohol extracts were 0.0031 wt% and 0.0033 wt% respectively.…”

“…The glass temperature of PAA hydrogel was determined by DSC and DTA characterisations 58. The phenomenon of shape memory occurred only in the case where the percolation of hydrogel particles took place.…”