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We report on measurements of relaxation times of nanometer-sized deformations resulting from the impact of individual energetic ions on poly͑methyl methacrylate͒ surfaces at temperatures close to and below the glass transition T g. The temporal evolution of the dimensions of the deformations is well described by a stretched exponential function, but with relaxation times ͑T͒ many orders of magnitude smaller than bulk values at the same T. The local T g was around 86°C, roughly 30°C below the conventional bulk T g. At the vicinity of the local T g , ͑T͒ follows the Vogel-Fulcher type of T dependence, but at lower T a transition towards a less steep behavior is seen.

Hybrid nanocomposites of polystyrene (PS) and methacryl phenyl polyhedral oligomeric silsesquioxane (POSS) were synthesized by reactive melt blending in the mixing chamber of a torque rheometer using dicumyl peroxide (DCP) as a free radical initiator and styrene monomer as a chain transfer agent. The effects of mixing intensity and composition on the molecular structure and morphology of the PS-POSS hybrid nanocomposites were investigated. The degree of POSS hybridization (a POSS ) was found to increase with the POSS content, DCP/POSS ratio, and rotor speed. For the PS-POSS materials processed in the absence of styrene monomer, an increase in the a POSS led to a reduction in the molecular weight by PS chain scission, as a consequence of the free radical initiation. On the other hand, the use of styrene monomer as a chain transfer agent reduces the steric hindrance in the hybridization reaction between POSS and PS, enhancing the degree of POSS hybridization and avoiding PS degradation. The PS-POSS morphology consists of nanoscale POSS clusters and particles and microscale crystalline POSS aggregates. PS-POSS with higher a POSS values and lower amounts of nonbound POSS showed improved POSS dispersion, characterized by smaller interfacial thickness (t) and greater Porod inhomogeneity lengths (l p ). The processing-molecular structure-morphology correlations analyzed in this study allow the POSS dispersion level in the PS-POSS materials to be tuned by controlling the reactive melt blending through the choice of the processing conditions. These insights are very useful for the development of PS-POSS materials with optimized performance.

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