Self-assembling nano mixed-brushes having co-continuous surface morphology by melt growing single crystals and comparison with solution patterned leopard-skin surface morphology

Abstract

Self-assembled mixed-brushes with co-continuous surface morphologies were developed from melts of poly(ethylene glycol)-b-polystyrene (PEG-b-PS) and poly(ethylene glycol)-b-poly(methyl methacrylate) (PEG-b-PMMA) diblock copolymers by a self-seeding technique. Some features of solution-grown matrix-dispersed mixed-brushes having controllable characteristics were briefly recalled and compared with the behavior of the corresponding melt-grown mixed-brushes. The observations implied that some major differences exist between the two growth systems. An obvious deduction made from atomic force microscopy (AFM) height images was that the patterned leopard-skin like surface morphology of the solution-induced mixed-brush single crystals changed to a co-continuous morphology in the melt state. Beside the alteration of the growth environment from solution to melt, this phenomenon was assigned to the dominant kinetic effect which replaced the thermodynamic effect that prevailed in the dilute solution systems. The ratio of PMMA- to PS-covered surface area on the substrate increased from 20/80 for the solution-grown mixed-brush single crystals to 50/50 for the melt-grown ones. Owing to an accelerated kinetic effect, the thickness of a melt-grown mixed-brush single crystal was significantly greater than that observed for a solution-grown mixed-brush single crystal of the same molecular weight. Similar trends, nevertheless, were observed for the thickness changes with molecular weight and crystallization temperature. The lateral sizes of the melt-grown single crystals were about 4-fold larger than those of the solution-grown single crystals (e.g., 24 vs. 6 μm). The thicknesses were also proven by the interface distribution function of small angle X-ray scattering analysis.