Experimental investigation of the structural features of polycarbonate (PC) filled with bismuth nitrate pentahydrate (BNP) composite films in terms of free volume defects probed by positron annihilation lifetime spectroscopy.

The effect of bismuth nitrate pentahydrate (BNP) on the properties and microstructural features of polycarbonate (PC) has been investigated using PALT, XRD, SEM, EDX, TG, ATR-FTIR and tensile mechanical measurements. Positron Annihilation Lifetime Spectroscopy reveals that the ortho-positronium lifetime and its corresponding intensity significantly decrease as the filler level of BNP in PC (in the composite) increases from 0.3 wt% up to 5.0 wt%. This is due to the increasing fraction of positrons that annihilate with the filler particles and also in the interfacial layers of the filler and the host polymer. Fourier Transform Infrared spectra show that there is no significant shift in the IR bands of the composite when compared to those of pure PC, and so there is little molecular level interaction between PC and BNP. The micrographs of SEM revealed a random distribution of filler particles in the composite, and there is the formation of agglomerates of BNP at higher filler levels. There is an increase in the degree of crystallinity of the composite films due to the addition of the crystalline filler, which was confirmed by XRD analysis. Tensile mechanical tests confirmed the improved tensile strength of prepared composites at lower and moderate filler levels, from 0.0 wt % up to 2.5 wt%. The free volume properties of the composite films are correlated with its tensile mechanical properties.