Theoretical and experimental investigations of shape memory characteristics of miscible rubber-wax blends

Shape Memory Polymers (SMPs) are smart materials capable of transforming back to their intended shape and therefore, are used to replicate biomimetic functionalities in synthetic materials. Here, we demonstrate that polymer blending can be used as an effective technique to design SMPs. In particular, the blends consists of wax and rubber that signify soft and hard segments of the SMP, respectively. In particular, we use the standard linear viscoelastic model where the two constituents, rubber represented by Hookean spring and wax represented by Maxwellian liquid, are connected in parallel; hence, we assume that the contribution of each component in the total stress is distributed in proportion of the composition. Via simulation, we establish that wax and rubber, individually do not exhibit shape memory behavior but do so upon blending; the shape memory behavior is qualitatively validated from experiments. We also confirm that the shape memory properties of our rubber-wax blends, namely, the shape fixity and shape recovery ratios at different concentrations, is in qualitative agreement with the properties of SMPs. Our findings indicate that polymer blending can be seen as an alternative strategy to design SMPs; the properties of these polymers can be varied directly by changing the composition of the blend.