Investigating the role of compression rates in pressure induced polymerization of crystalline acrylamide using ab-initio molecular dynamics

Pressure-induced transformations in molecular crystals with varying pressure increase rates (PIRs) can enable the kinetic control of the obtained phase. Herein, we investigate the dependence of PIR on the pressure-induced polymerization of acrylamide. 0 K optimizations and room temperature molecular dynamics simulations at two different PIRs are used to characterize the structural evolutions and transformation mechanisms. Quasi-static compression at 0 K suggests polymerization to a 3-dimensional polymer, whereas rapid compression indicates the existence of multiple metastable polymers with lower activation barriers for polymerization. Room temperature ab initio MD simulations led to different structural evolutions based on the applied PIR. Although both compression pathways eventually yield the same metastable polymer, rapid compression results in disordered polymers. The mechanism of formation as well as the structural and electronic properties of the various polymers obtained are characterized. Our results suggest a hierarchical route towards the thermodynamic polymer through other metastable polymers.