Kinetics of phase transitions

General introduction

Phase transitions are all around us and fascinating for many reasons. From cloud formation to ice nucleation they play an important role in natural processes. For many years, the theoretical framework to explain the transition from one phase of matter to another has been classical nucleation theory (CNT). CNT aims to compute the work associated to the formation of a small nucleus in an initial metastable phase. From the past 20 years, considerable improvements were made in both numerical and experimental methods, which allow us to get more insights into the microscopic pathways during a phase transition. Interestingly, the resulting picture is more complex than the simple one step nucleation process imagined before.

Crystallization under shear flow

The goal of this study is to quantify the role of shear in crystallization kinetics and whether shear induces or suppresses crystallization. To answer these questions, we employ molecular dynamics simulations to study the crystallization kinetics of a nearly hard sphere liquid that is weakly sheared. The snapshots show that shear flow (left: without, right: weak shear flow) can enhance crystallization at sufficiently high densities.

References

  • The role of shear in crystallization kinetics: From suppression to enhancement
    D. Richard and T. Speck
    Sci. Rep. 5, 14610 (2015)
    abstract preprint
  • Crystallization in a sheared colloidal suspension
    B. Lander, U. Seifert, and T. Speck
    J. Chem. Phys. 138, 224907 (2013)
    abstract preprint

Phase separation in active Brownian particles

Collective behavior in active matter leads also to nucleation and pattern formation. Since we deal most of the time with strongly driven systems, it is not straightforward to make any analogy to equilibrium nucleation. Therefore we aim, for a minimal model exhibiting a 'gas-liquid' phase separation, to explore the kinetics and relevant order parameters leading to a reactive transition.