Role of copper content on EPR, susceptibility and optical studies in poly(vinylalcohol) (PVA) complexed poly(ethyleneglycol) (PEG) polymer films

Polymer films of poly(vinylalcohol) (PVA) complexed with poly(ethyleneglycol) (PEG) with different dopant concentrations of Cu2+ ions are prepared by solution casting technique. Improvement in the crystallinity of the samples is observed with the X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. Thermal transition and thermal degradation of the films with respect to copper concentration were studied by Differential Scanning Calorimetry (DSC) and thermo gravimetric analysis (TGA). The change in glass transition temperature (Tg) as a function of copper concentrations (x = 1–5 mol%) has been attributed to branching and steric effects in PVA + PEG complexes. In TGA curves low thermal degradation in the samples has been observed with high copper content. The EPR spectra of all the polymer samples exhibit resonance signals characteristic of Cu2+ ions. The spin-Hamiltonian parameter, indicate that the ground state of Cu2+ ions is d x 2 - y 2 and the site symmetry around Cu2+ ions is tetragonally distorted octahedral site. The spin concentration (N) participating in the resonance is measured as a function of temperature and it obeys Boltzmans law. The paramagnetic susceptibility (χ) is calculated from the EPR data at various temperatures and the Curie constant (C) is evaluated. The optical absorption spectrum exhibits a broad band at 784 nm which is assigned to the 2B1g → 2B2g transition.