Free volume and lamellar structure of poly vinyl alcohol-nanosized BaTiO3 composite: Positron annihilation and small angle X-ray scattering study

Abstract

The sub-nanoscopic free volume structure of poly vinyl alcohol (PVA) matrix in its composite with nanosized BaTiO3 (BT loading 0.2, 0.6, 1.0 and 2.0wt%) is investigated using positron annihilation lifetime spectroscopy (PALS). The lamellar structure of PVA matrix at nm scale is investigated using Small Angle X-ray Scattering (SAXS) technique. The results indicate that the free volume and lamellar structure of PVA matrix is significantly altered even at very low BT loading (0.2wt%) due to attractive interfacial interaction. The variations observed in the free volume characteristics are consistent with the existing theory of polymer-nanocomposites i.e. at low filler loading, the polymer-nanocomposites’ dynamics is polymer like with increased friction and a constrained interphase is created around the filler particles. The SAXS results supplemented by differential scanning calorimetry measurements show that the crystallization in PVA is altered due to physical restriction imposed by BT particles on PVA chains. These results are supported by the crystallinity measurements using X-ray diffraction technique.