Influence of C-60 fullerenes on the glass formation of polystyrene

Alejandro Sanz, Him Cheng Wong, Alisyn J. Nedoma, Jack F. Douglas, Joao T. Cabral

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review


We investigate the impact of fullerene CH on the thermal properties and glass formation of polystyrene (PS) by differential scanning calorimetry (DSC) and dielectric spectroscopy (DS), for CH concentrations up to 30% mass fraction. The miscibility and dispersibility thresholds of PS/C-60 nanocomposites are first estimated by a combination of microscopy, small angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS) experiments, and these thresholds were found to be similar or equal to 1 mass% and similar or equal to 4 mass% C-60, respectively. The addition of C-60 increases the glass-transition temperature (T-g) of rapidly precipitated PS composites, up to a `threshold' C-60 concentration (similar or equal to 4 wt in agreement with the dispersibility estimate). Beyond this concentration, the T-g reverts gradually towards the neat PS value. We present a comprehensive study for composites based on PS of molecular mass 270 kg/mol, and demonstrate the generality of the impact of CH on T-g for PS matrices of 2 and 20 kg/mol. Thermal annealing or slowly evaporated composites largely reverse these effects, as the dispersion quality decreases. The dynamic fragility m of the composite is found to increase in the presence of C-60, but the scaling of m with T-g for PS is retained. Similarly, physical ageing experiments show a reduction of relaxation enthalpy in the glass regime, which is largely accounted for by the increase of T-g with C-60. The slowing down of the PS alpha-relaxation with C-60 contrasts with the local `softening' indicated by former Debye-Waller measurements and increase in fragility m. This effect is opposite to that of antiplasticizer additives, which both stiffen the material in the glassy state and reduce T-g, and simulations suggest this could be due to an increase in packing frustration. Finally, we review observations on the effect of nanoparticles on the T-g of PS and discuss the non-universal nature of T-g shifts by various types of nanoparticles. (C) 2015 The Authors. Published by Elsevier Ltd.
TidsskriftEuropean Polymer Journal
Sider (fra-til)47-56
Antal sider10
StatusUdgivet - 26 jun. 2015
Udgivet eksterntJa

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