# Non-monotonic effect of additive particle size on the glass transition in polymers

## TL;DR

This study uses molecular dynamics simulations to reveal that the size of additive particles non-monotonically influences the glass transition and relaxation dynamics in polymers, highlighting the importance of monomer-scale packing effects.

## Contribution

It demonstrates the non-monotonic impact of additive particle size on polymer relaxation and glass transition, providing insights into the underlying microscopic mechanisms.

## Key findings

- Non-monotonic change in relaxation dynamics with particle size
- Non-monotonic effect on glass transition temperature in entangled chains
- Size effects linked to monomer-scale packing phenomena

## Abstract

Effect of small additive molecules on the structural relaxation of polymer melts is investigated via molecular dynamics simulations. At a constant external pressure and a fixed number concentration of added molecules, the variation of particle diameter leads to a non-monotonic change of the relaxation dynamics of the polymer melt. For non-entangled chains, this effect is rationalized in terms of an enhanced added-particle-dynamics which competes with a weaker coupling strength upon decreasing the particle size. Interestingly, cooling simulations reveal a non-monotonic effect on the glass transition temperature also for entangled chains, where the effect of additives on polymer dynamics is more intricate. This observation underlines the importance of monomer-scale packing effects on the glass transition in polymers. In view of this fact, size-adaptive thermosensitive core-shell colloids would be a promising candidates route to explore this phenomenon experimentally.