The interplay of thermodynamics and kinetics: Imparting hierarchical control over film formation of self-stratified blends

Spin casting is an attractive method to fabricate thin films found in electronic devices. Recent results investigate the impact of spin casting parameters on final film structure, and proved the impact of casting speed and molecular weight on film structure are due to the thermodynamic properties of surface energy and miscibility of the polymer blend, respectively. To determine the overarching thermodynamic property controlling final film structure, we monitor final film structures developed from the polymer blend of poly(3-hexylthiophene-2,5-diyl) and poly(methyl methacrylate) at controlled loading ratios, relative molecular weights, and casting speed. The structures of these thin films were characterized via neutron reflectivity, and the results show that at the fastest casting speed, enthalpy and surface energy of the blend dictate final film structure, and at the slowest casting speed, there is less control over the film orientation due to multiple thermodynamic properties simultaneously driving the stratification. These results broaden the current correlation between spin casting parameters and final polymer thin film architecture, providing routes to polymer thin film fabrication protocols that result in targeted structures.