(180bu) Effect of Nanoparticles On Rubber Mechanics

Addition of nanoparticles has been shown to reduce polymer melt viscosity.  This phenomena is poorly understood but is often associated with R_c/R_g<1, h/R_g<1 and Mw/Mw_e>1 where R_c is the particle radius, R_g is the polymer radius of gyration in the bulk h is the particle’s average surface to surface separation Mw is the polymer molecular weight and Mw_e is the polymer entanglement molecular weight. In addition polymer segments must have a weak enthalpy of attraction with the particle surface.  This last requirement renders the particle solubility marginal such that above a certain particle concentration, increases in viscosity are often associated with particle aggregation. Here we explore the effects of addition of weakly soluble nanoparticles on the mechanics of rubber.  Using a commercial RTV PDMS system we explore the effects of adding nanoparticles up to their solubility limit on the kinetics of polymerization, and linear elastic moduli as a function of particle concentration.  We start by demonstrating that particle addition reduces the viscosity of the PDMS polymer melt prior to cross linking and then explore the effects of the nanoparticles on kinetics of polymerization, the effective crosslink density and loss tangent.  Our goal is to develop an understanding of how the nanoparticles alter polymer chain dynamics within the rubber and how the nanoparticles can be used to tune rubber mechanical properties.