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WLF to Arrhenius dynamic transition in nanocomposites

AuthorsBaeza, Guilhem P.; Alegría, Ángel ; Vlassopoulos, Dimitris
Issue Date2015
Citation87th Annual Meeting of The Society of Rheology (2015)
AbstractWe investigate the dynamics of nanocompositesconsisting of poly(2 vinyl pyridine), P2VP, matrix and well dispersed nanosilica spheres by means of rheology and dielectric spectroscopy. Master curves are obtained via time-Temperature superposition but, remarkably, the temperature dependence of the frequency shift factors changes from William-Landel-Ferry behavior to an Arrhenius-like as the filler fraction increases (to about 50%wt). Dielectric spectroscopy reveals a significant decrease in the strength of the alfa-process and its broadening at lower frequency (called alfa2) becoming noteworth at high silica content. The significant dynamic change with increased silicia loading implies strong physico-chemical interactions between silica particles and polymer matrix. NMR and FTIR revealed the presence of physical H-bond between silanols at the silica surface and nitrogen atoms of the P2VP chains, which we clain to give rise to the bridging of particles through the polymer chains forming a network. this is consistente with recent results suggesting a transitionfrom soft to glassy bridges in the same nanocomposites system at the same filler fraction. The huge activation energy of about 380 kJ/mol is rationalized by estimating the density of bonds per particle and polyner chain, yielding a "Velcro" picture for the network. The effects of matrix molar mass and nonlinear strain are also addressed.
DescriptionResumen del trabajo presentado al 87th Annual Meeting of The Society of Rheology, celebrado en Baltimore (USA) del 11 al 15 de octubre de 2015.-- et al.
Appears in Collections:(CFM) Comunicaciones congresos
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