Effects of particles on spinodal decomposition: A Phase field study

Abstract

In this thesis, we study the interplay of phase separation and wetting in multicomponent systems. For this purpose, we have examined the phase separation pattern of a binary mixture (AB) in presence of stationary spherical particles (C) which prefers one of the components of the binary (say, A). Binary AB is composed of critical composition(50:50) and off-critical compositions(60:40, 40:60). Particle sizes of 8 units and 16 units are used in the simulations. Two types of particle loading are used, 5\% and 10\%. We have employed a ternary form of Cahn-Hilliard equation to incorporate immobile fillers in our system. To elucidate the effect of wetting on phase separation we have designed three sets of $χ_{ij}$ and $κ_{ij}$ to include the effects of neutral preference, weak preference and strong preference of the particle for one of the binary components. If the particles are preferentially wetted by one of the components then early stage microstructures show transient concentric alternate layers of preferred and non-preferred phases around the particles. When particles are neutral to binary components then such a ring pattern does not form. At late times, neutral preference between particles and binary components yields a continuous morphology whereas preferential wetting produces isolated domains of non-preferred phases dispersed in a continuous matrix of preferred phase. For off-critical compositions, if minor component wets the particle then a bicontinuous morphology results whereas if major component wets the network a droplet morphology is seen. When majority component wets the particle, a possibility of double phase separation is reported. In such alloys phase separation starts near the particle surface and propagates to the bulk at intermediate to late times forming spherical or nearly spherical droplets of the minor component.