Double Glass Transitions and Interfacial Immobilized Layer in in-Situ-Synthesized Poly(vinyl alcohol)/Silica Nanocomposites

Abstract

The results of dynamic mechanical analysis (DMA) revealed that there were double tan δ peaks in the poly(vinyl alcohol)(PVA)/silica nanocomposite samples at low frequencies. The two relaxations attribute to glass transition for PVA matrix and motions of segments for PVA chains confined by the surface of silica nanoparticles, respectively. The thickness of the interfacial immobilized layer was calculated, and schematic models were founded, which can well interpret the results. The changes of the two relaxations with various silica contents at different frequencies are discussed. It is considered that most of the interfacial PVA chains probably span the two layers. The peak position of the first relaxation moves to high temperature with the increase of frequency for strain lag of the sample whereas the second one shifts to low temperature for the “drag effect” between the intrinsic and interfacial segments of the spanned PVA chains.