A novel method was developed to detect the glass transition of thin and ultrathin polystyrene (PS) films by correlating the relationships between the temperature-dependent viscoelasticity of the PS films and stick–slip behavior on their surfaces during dynamic wetting of glycerol or oligo-poly(ethylene glycol) droplets. The peak temperature (T jm) obtained from the jumping angle–film temperature curve, in which the jumping angle Δθ was employed to scale the stick–slip behavior, was nearly identical to the corresponding T g (or T α) of the PS film. This was confirmed by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The change of the measured T jm with film thickness and substrate chemistry (SiO2–Si and H–Si) further confirmed that the developed method is very sensitive for detecting the dynamics of ultrathin polymer films.

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 À1 , respectively, which are higher than those of the non-micellized PMMA free chains (70 C and 164 kJ mol À1 ). 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.

The effect of the concentration of casting solutions on the surface dynamics of the corresponding spin-coated poly(methyl methacrylate) (PMMA) film was investigated by measuring the surface reorganization of fluorine tracer-labeled PMMA. The onset temperature of fluorinated PMMA chain end reorganization (T(onsetR)) was identified and is shown to depend on the PMMA concentration in the film-forming solution. It was found that the surface T(onsetR) and relaxation activation energy E(a) of the PMMA films prepared from 4.2 wt% PMMA cyclohexanone solution are 70 °C and 260 kJ mol(-1), respectively, which are higher than those of the PMMA films prepared from 0.8 wt% PMMA cyclohexanone solution (55 °C and 144 kJ mol(-1), respectively). The T(onsetR) and E(a) of PMMA films increased with increasing concentration of casting solutions within the range of 1.8 wt% to 4 wt%. The chain entanglement of PMMA chains is proposed to be the speculative origin for these observed depressed dynamics of poly(methyl methacrylate) chains on the films' surface prepared using casting solutions of various concentrations.