Dynamics, thermal behaviour and elastic properties of thin films of poly(vinyl alcohol) nanocomposites

Abstract

A combined differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and laser-interferometric creep rate spectroscopy (CRS) approach has been utilised to study the dynamics, thermal behaviour and elastic properties of thin films (0.05–0.10 mm) with poly(vinyl alcohol) (PVA) based nanocomposites at temperatures ranging from 20 to 180–220 °C. 3D amorphous fumed silica (nanoparticles of ∼9 nm in average diameter, specific surface area S_BET = 330 m² g⁻¹, bulk density ρ_b = 0.045 g cm⁻³) initial and compacted by mechanochemical activation to ρ_b = 0.32 g cm⁻³ (dense nanosilica with a small change in S_BET), and exfoliated graphite (oxidised 2D sheets packed in stacks of approximately 200 nm in thickness) were used as nanofillers of the PVA films at content of 1, 10 or 20 wt%. The impact of nanofillers which significantly modified structure, dynamics and other properties of the PVA matrix due to constrained dynamics effects depends on the filler type and concentration. The most detailed, discrete pictures of the dynamics and pronounced dynamics heterogeneity in the glass transition of the composites were shown by the CRS method. At any temperature within the 20–180 °C range, the composite modules changed by an order of magnitude. Up to a 14 °C rise of the glass transition temperature was observed for the nanocomposites. The most dramatic enhancing effect of elastic and creep resistance properties was attained for a composite incorporating 10 wt% of exfoliated graphite.