Isaac Newton Institute for Mathematical Sciences

Phase transition kinetics and polydispersity

Presenter: John J. Williamson (University of Leeds)

Co-author: R. M. L. Evans

Abstract

Polydispersity -- the continuous non-identicality of ostensibly similar particles -- is a pervasive complication in the study of colloids and other soft matter. We use Kinetic Monte Carlo simulation to take a "kinetics-focused" approach to polydispersity (and phase transitions generally), in contrast to predominantly equilibrium existing work. Our key findings are:

  1. A wide class of free energy landscapes can give rise to a split crystal-gas-liquid interface during growth; moreover the effect of the gas layer on growth rate is qualitatively altered by a small degree of polydispersity, an effect explained by novel measurements of fractionation and local particle size correlations
  2. Fractionation (de-mixing) of polydisperse particles, traditionally conceived of as a slow relaxation, can occur even in the earliest stages of spinodal decomposition, and inter-particle potentials which are identical in the monodisperse case may be "split" by polydispersity to give rise to opposite fractionation effects.