Disentangling the Calorimetric Glass-Transition Trace in Polymer/ Oligomer Mixtures from the Modeling of Dielectric Relaxation and the Input of Small-Angle Neutron Scattering

Abstract

We have disentangled the contributions to the glass transition as observed by differential scanning calorimetry (DSC) on simplified systems of industrial interest consisting of blends of styrene-butadiene rubber (SBR) and polystyrene (PS) oligomer. To do this, we have started from a model previously proposed to describe the effects of blending on the equilibrium dynamics of the alpha-relaxation as monitored by broadband dielectric spectroscopy (BDS). This model is based on the combination of self -concentration and thermally driven concentration fluctuations (TCFs). Considering the direct insight of small-angle neutron scattering on TCFs, blending effects on the alpha-relaxation can be fully accounted for by using only three free parameters: the self-concentration of the components q)self SBR and q)selfPS) and the relevant length scale of segmental relaxation, 2Rc. Their values were determined from the analysis of the BDS results on these samples, being that obtained for 2Rc approximate to 25 angstrom in the range usually reported for this magnitude in glass-forming systems. Using a similar approach, the distinct contributions to the DSC experiments were evaluated by imposing the dynamical information deduced from BDS and connecting the component segmental dynamics in the blend above the glass-transition temperature Tg (at equilibrium) and the way the equilibrium is lost when cooling toward the glassy state. This connection was made through the alpha-relaxation characteristic time of each component at Tg, tau g. The agreement of such constructed curves with the experimental DSC results is excellent just assuming that tau g is not affected by blending.