Phase behaviour of Shape Memory Polymer-Nanoparticle Ternary Blends*

Shape memory polymers (SMPs) are a class of smart materials that have been extensively used in a variety of biomedical applications. Typically, the shape changes in SMPs are through phase transformation that is triggered by an external stimulus. SMPs that use a non-invasive trigger, like magnetic field, are therefore desirable in biocompatible stents, implants, etc. Here, we simulate the shape memory behavior of binary polymer blends with magnetic nanoparticle (NP) fillers and investigate the role of magnetic field on polymer-polymer-NP compatibility, which inturn affects its shape memory performance. Our approach harnesses Flory-Huggins theory of mixing for polymer interactions, combined with free energy formulation of spherical NPs. In particular, we construct the phase diagram of the SMP blends and determine the optimized SMP characteristics as a function of NP concentration and magnetic field strength. We demonstrate that the shape fixity and recovery ratios can be tailored for the existing SMP blends by tuning the composition of NPs. Our findings can be used to design and predict the characteristics of SMP blends to be used as biomechanical devices.