Papers by Author: Hans Grande

Abstract: We report the phase behavior of nanocomposites composed of weakly-charged flexible polymers and polar nanoparticles by extending a mean-field theory for all-polymer nanocomposites recently introduced (Journal of Nano Research 2 (2008) 105). Translational, nanoparticle-driven, electrostatic and enthalpic interaction effects are taken into account. Weakly-charged polymers are predicted to be miscible with polar nanoparticles about one order of magnitude larger (in radius) than conventional uncharged polymers, even in the presence of moderate unfavorable enthalpic interactions. The detrimental effect of addition of a low molecular weight monovalent 1-1 salt on nanocomposite miscibility is also evaluated.

Abstract: The miscibility behaviour of polymer-nanoparticle / linear-polymer blends (all-polymer nanocomposites) has been investigated using an incompressible mean-field theoretical model that accounts for combinatorial, temperature-dependent exchange interaction energy and nanoparticle-driven effects. The theory is employed to predict the phase diagram of poly(styrene)-nanoparticle (PS-np) / linear-poly(vinyl methyl ether) (PVME) nanocomposites from room temperature to 675 K. Complete miscibility is predicted for PS-nanoparticles with radius < 6 nm blended with PVME (molecular weight 62 500 g/mol, nanoparticle volume fraction 20 %). The effect of PVME molecular weight and blend composition on the miscibility diagram is also addressed. When compared to the well-known experimental phase diagram of linear-PS / PVME blends displaying lower critical solution temperature (LCST) behaviour, the miscibility improving effect of sub-10 nm PS-nanoparticles is clearly highlighted. In terms of the model, this favourable nanoscale effect arises mainly from the reduced stretching induced by the sub-10 nm nanoparticles and the increased exothermic contacts when compared to nanoparticles with sizes > 10 nm.