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Abstract

Shape memory polymers (SMP) are fascinating materials, which are able to recover large shape changes. In contrast to metallic shape memory materials, where the recovery of the original programmed shape is triggered by a diffusion free (martensitic) phase transformation, the shape memory effect in polymers has an entropic origin. Upon heating above the glass transition temperature, low entropic elongated polymers become sufficiently mobile to recover a high entropic spherical conformation. We address this topic using both experiments [1] and atomistic computer simulations [2]. It is shown via spectroscopy experiments that additive molecules dramatically alter the distribution of hydrogen bonds in the polymer matrix, thereby changing the shape memory switch temperature. These findings are in line with results obtained from MD simulations. Moreover, simulations also reveal interesting dependence on the size of additive molecules [3]. [1] H. Dumlu, A. Marquardt, E. M. Zirdehi, F. Varnik, Y. Shen1, K. Neuking and G. Eggeler, A Mechanical Analysis of Chemically Stimulated Linear Shape Memory Polymer Actuation, Materials 14, 481 (2021) [2] E. Zirdehi, F. Varnik, Non-monotonic effect of additive particle size on the glass transition in polymers, J. Chem. Phys. 150, 024903 (2019). [3] E. M. Zirdehi, H. Dumlu, G. Eggeler, F. Varnik, On the Size Effect of Additives in Amorphous Shape Memory Polymers, Materials 14, 327 (2021)