[SY-H1] Symposium H-1

[SY-H1] Non-monotonic particle size effect on the glass transition in polymer-particle blends and its application to shape memory polymers

^○Elias M. Zirdehi, Fathollah Varnik (Ruhr-University Bochum, Germany)

Both via experiments and molecular dynamics simulations, it is shown that adding small molecules enhances the dynamics of structural relaxation in polymer melts and glasses [1]. While this effect is a monotonic function of concentration [1], it is found to be a non-monotonic function of particle size [2]. A detailed survey of non-Gaussian parameter for small molecules and polymer beads reveals a separation of time scales for cooperative motion between the above two species. This is indicative of a decoupling of the fast dynamics of small molecules from the chains’ relaxation dynamics and a resulting weak effect. The dynamics of large particles, on the other hand, is strongly coupled to that of polymer. However, since large particles are only slightly more mobile than the polymer beads, their enhancing effect is also relatively weak. For intermediate particle sizes, the particles are sufficiently fast and the coupling to polymer strong enough to induce a large enhancement of the chains' relaxation kinetics. This non-monotonic effect occurs both for entangled and non-entangled polymers, hinting towards local packing effects as the main origin of the phenomenon [1]. It is shown that the effect can be explored in shape memory polymers to tune the triggering temperature of the shape recovery process in a non-monotonic manner.

[1] Elias M. Zirdehi, Axel Marquardt, Gunther Eggeler and Fathollah Varnik, Molecular dynamics simulations of entangled polymers: The effect of small molecules on the glass transition temperature, Procedia Computer Science 198C, 265 (2017).

[2] Elias M. Zirdehi and Fathollah Varnik, Non-monotonic particle size effect on the glass transition in polymer-particle blends (submitted).