Positron annihilation studies of free volume changes accompanying the incorporation of lead nitrate in PVA-PVP polymeric blend

Lead nitrate (Pb(NO3)2) – filled polyvinyl alcohol (PVA) – polyvinyl pyrrolidone (PVP) composite films were prepared by solution casting method, with filler levels (FL) varying from 2.7 wt% up to 42.7 wt%. Positron annihilation lifetime spectroscopy and measurements of Doppler broadening of annihilation radiation (DBAR) were carried out to monitor the changes in polymer microstructure due to the filler loading. The lineshape parameter, S, increased at lower doping levels, followed by a decrease at higher FL due to the effects of the filler (Pb(NO3)2) on the microstructure of PVA-PVP composite films. A significant drop in the intensity (I3) of the ortho-positronium (o-Ps) component, from 18% down to approximately 2%, is observed on increasing the FL from 16.2 up to 26.7 wt%. This is accompanied by a decrease in the intensity (I1) of the shortest lifetime component and a compensating increase in intensity (I2) of the intermediate lifetime component. It indicated the inhibition of positronium (Ps) formation in Pb(NO3)2-filled PVA-PVP composites. •Lead nitrate filled PVA-PVP composite films are studied using PALS and DBAR.•Significant changes are observed in positron parameters due to filler loading.•Intensity of o-Ps component decreases from 18% to 2%, at higher filler levels (FL).•Inhibition of positronium (Ps) formation is observed for FL beyond 19.8 wt%.•Ps trapping rate in the composite decreased significantly at moderate and high FL.