Suppressed surface dynamics of poly(methyl methacrylate) chains in the corona of collapsed dry micelles tethered by a fluorinated block core

Abstract

The effect of chain constraint on the surface dynamic of poly(methyl methacrylate) (PMMA) was investigated in the context of polymer tethering to a micelle core. Film surfaces dominated by either poly(methyl methacrylate) (PMMA) tethered by a poly(2-perfluorooctylethyl methacrylate) (PFMA) micelle core or non-micellized free PMMA chains are fabricated by spin coating a solution of PMMA end-capped with various numbers of FMA units onto silica substrates. By measuring the surface rearrangement kinetics of these films under thermal annealing, the onset temperature of rearrangement (T^onset_R) and the activation barrier for relaxation (E_a) of surface PMMA chains are determined. It is found that the T^onset_R and E_a of the PMMA micellized chains are 83 °C and 317 kJ mol⁻¹, respectively, which are higher than those of the non-micellized PMMA free chains (70 °C and 164 kJ mol⁻¹). The T^onset_R and E_a of PMMA in the corona increase linearly with increasing compactness of the PFMA core. The higher T^onset_R and E_a values demonstrate the reduced mobility of surface PMMA segments tethered to a micelle core. The constraint of conformational freedom, reduction of free volume and increment of chain packing density are proposed as the speculative origins for this depressed dynamic of poly(methyl methacrylate) chains in the corona of collapsed dry micelles tethered by fluorinated block core.