Fundamentals of Phase Separation in Polymer Blend Thin Films

In this Ph.D. thesis, I investigate fundamental aspects of phase separation in polymer-blend thin films by unifying 1D phase equilibria with film evolution phenomena. I begin by extending a Hamiltonian phase portrait method, useful for visualising and calculating phase equilibria of polymer-blend films, allowing the method to be applied to systems with no convenient symmetries. Consideration of equilibria suggests a thermodynamic mechanism of film roughening, whereby laterally coexisting phases could have different depths in order to minimise free energy. I then make use of the phase portraits to demonstrate that simulations of lateral phase separation via a transient wetting layer, which conform very well with experiments, can be satisfactorily explained by 1D phase equilibria and a surface bifurcation mechanism involving effective boundary conditions caused by the film surfaces. Lastly, to tie together the aforementioned work, I introduce a novel 3D model of coupled phase separation and dewetting, for which I solved the problem of including a general non-uniform composition profile in the depth direction between the film surfaces. Pattern formation, in which surface roughening shadows the phase separation, seems to be determined by an interplay between dewetting kinetics and underlying phase equilibria.