Chemo-mechanical coupling effects in shape memory polymers: Molecular dynamics simulations versus experiments
Fathollah Varnik, ICAMS, Ruhr University Bochum, Bochum, GermanyElias M. Zirdehi, ICAMS/Ruhr University Bochum, Bochum, GermanyAxel Marquardt, IFW/Ruhr University Bochum, Bochum, GermanyNeuking Klaus, IFW/Ruhr University Bochum, Bochum, GermanyGunther Eggeler, IFW/Ruhr University Bochum, Bochum, Germany
Shape memory polymers (SMPs) are capable of recovering a programmed initial shape. In many applications, temperature is raised to trigger the shape recovery process. Here, we show via molecular dynamics simulations of a coarse-grained model for SMPs that the penetration of small additive molecules into a shape memory polymer can reduce the glass transition temperature, thereby triggering the shape recovery process as a certain threshold concentration is reached. This issue is also addressed via carefully designed experiments on a polyurethane SMP. Remarkable agreement is found between simulations and experiments. Simulations also predict a non-monotonic effect of the size of additive molecules on the glass transition. These results open a qualitatively new perspective in designing advanced shape memory materials based on a mixture of polymers and small additive molecules.