Plasticization effect of C60 on the fast dynamics of polystyrene and related polymers:: an incoherent neutron scattering study

We utilize inelastic incoherent neutron scattering (INS) to quantify how fullerenes affect the 'fast' molecular dynamics of a family of polystyrene related macromolecules. In particular, we prepared bulk nanocomposites of (hydrogenous and ring-deuterated) polystyrene and poly(4-methyl styrene) using a rapid precipitation method where the C-60 relative mass fraction ranged from 0% to 4%. Elastic window scan measurements, using a high resolution (0.9 mu eV) backscattering spectrometer, are reported over a wide temperature range (2-450 K). Apparent Debye-Waller (DW) factors < u(2)>, characterizing the mean-square amplitude of proton displacements, are determined as a function of temperature, T. We find that the addition of C-60 to these polymers leads to a progressive increase in < u(2)> relative to the pure polymer value over the entire temperature range investigated, where the effect is larger for larger nanoparticle concentration. This general trend seems to indicate that the C-60 nanoparticles plasticize the fast (approximate to 10(-15) s) local (approximate to 1 angstrom) dynamics of these polymer glasses. Generally, we expect nanoparticle additives to affect polymer dynamics in a similar fashion to thin films in the sense that the high interfacial area may cause both a speeding up and slowing down of the glass state dynamics depending on the polymer-surface interaction.