Positron lifetime and third-order nonlinear optical studies of P(St-co-MMA)/NiO polymer nanocomposites

Abstract

Polymer nanocomposites of Poly(styrene-co-methylmethacrylate) (P(St-co-MMA))/Nickel oxide (NiO) with different NiO nanoparticles wt% (0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) are prepared by solution casting technique. The UV–Vis and XRD results revealed decreased direct energy band gap, increased Urbach energy and decreased crystallinity with the increased NiO nanoparticles wt%. The SEM results show the agglomeration of nanoparticles for higher concentrations of NiO nanoparticles loading. The Z - scan studies show the increased nonlinear optical (NLO) parameters viz., nonlinear absorption coefficient (β), nonlinear refractive index (n2) and nonlinear susceptibility (χeff(3)) with increased NiO nanoparticles wt%. The free volume parameters viz., free volume (Vf) and fractional free volume (Fv) show increasing and decreasing trends with the NiO nanoparticles concentration respectively. The effect of free volume parameters on nonlinear optical parameters such as β,n2 and χeff(3) is brought out. The increased β,n2 and χeff(3) is due to the increased polarization by the NiO nanoparticles in P(St-co-MMA) polymer matrix. The decreased fractional free volume (Fv) with the increased NiO (wt%) indicates the increased packing density of polymeric chains of P(St-co-MMA) polymer matrix. The increased NLO parameters are attributed to the increased polarizability and packing density of polarizable groups in the P(St-co-MMA) polymer matrix.