On The evolution of phase separation in polymer blends

Abstract

An investigation is undertaken into the dynamics of phase separation in polymer blends in order to try to understand the morphologies produced via spinodal decomposition and to identify ways to target beneficial morphologies. Cahn-Hilliard theory is used with the Flory-Huggins free energy to model phase separating systems undergoing spinodal decomposition for a number of different systems. Initially a simple two component blend is studied undergoing spinodal decomposition via a temperature quench from the one phase to the two-phase region. The model is then used to study the process of secondary phase separation via a two-step quench process. A temperature quench from the one phase to the two phase region is undertaken and then the system is left to equilibrate for two different time periods before a quench further into the two phase region is carried out. The model is then extended to focus on the technologically useful process of reaction induced phase separation. In this case a two component polydisperse blend is quenched from the one phase to the two phase region via polymerisation of one component of the blend. The phase separation process is followed for selected reaction rates and the consequences of changing the final degree of polymerisation are studied both with and without the formation of a network in the reacting component of the blend. Finally a study of the effect of adding a surface into the blend is undertaken to show the development of a phase separated morphology at and near to the surface, we also present a method to overcome inconsistencies found in the Cahn-Hilliard model. The model is then used to target specific phase separated morphologies on a chemically patterned surface and to try and understand the processes involved in the phase separation of a three component, A B C, blend at a surface.