Formation of nanostructured thin films of immiscible polymer blends by directional crystallization onto a crystallizable organic solvent

Abstract

We show that epitaxial crystallization on a crystallizable solvent is a valuable method for achieving well-ordered nanoscale patterning in thin films of crystalline/amorphous immiscible polymer blends. Nanoscale patterning was achieved by cooling a hot solution of poly(l-lactic acid) (PLLA) and polystyrene (PS) in hexamethylbenzene (HMB) to a temperature below the melting temperature of HMB. Crystallization of HMB induced deposition of the polymers, directional crystallization of PLLA, and freezing of the progress of the phase segregation almost simultaneously, allowing the development of nanoscale well-oriented lamellar patterns. We compare the patterns formed in thin films of PLLA/PS immiscible blends with those formed in thin films of PLLA/poly(vinyl acetate) miscible blends and discuss the mechanism underlying the formation of ordered structures in immiscible blends in crystallizable solvents.