Microstructural, thermal, and free-volume properties of silver nanoparticle/reduced graphene oxide-loaded poly(vinyl alcohol)–poly(vinyl pyrrolidone)–carboxymethyl cellulose nanocomposites

Abstract This study reports the development of bio-based polymer nanocomposite films comprising a poly(vinyl alcohol)–poly(vinyl pyrrolidone)–carboxymethyl cellulose (PVA–PVP–CMC) ternary blend loaded with silver nanoparticles (Ag NPs) and reduced graphene oxide nanosheets (rGO NSs). Nanocomposites containing single and hybrid nanofillers (1–3 wt%) were fabricated via a solution casting technique. Structural analysis using XRD confirmed an average Ag NP crystallite size of 24.82 nm and a specific surface area (SSA) of 22.92 m 2 /g. The XRD patterns further confirmed the crystalline nature and purity of Ag NPs with an FCC structure and the graphitic rGO (002) reflection, while the nanocomposites exhibited predominantly amorphous characteristics with enhanced crystallinity upon filler incorporation, ranging from 5.99% for the pure blend to 15.07% for the film containing 3 wt% rGO NSs. FTIR revealed strong intermolecular hydrogen bonding among the polymer constituents and progressive interfacial interactions with the nanofillers, reflected in systematic shifts and intensity changes of the O–H, C = O, and C–O–C bands. SEM and EDX analyses of representative sample regions indicated generally uniform apparent dispersion and effective integration of the nanofillers within the polymer matrix. Thermal properties investigated by DSC showed a rise in Tg from 72.1 °C for the pure blend to 88.8 °C for the film containing 3 wt% Ag NPs, suggesting reduced polymer chain mobility resulting from strong interfacial interactions between the matrix and nanofillers. Free-volume characteristics evaluated by positron annihilation lifetime spectroscopy (PALS) showed that the ortho-positronium lifetime (τ 3 ) and corresponding free-volume size (V F ) ranged from 1.452 to 1.530 ns and 52.04–59.51 ų, respectively, across the filler series. The largest free volume was observed at 1 wt% Ag NP loading, indicating that low filler loading promotes free-volume formation, whereas higher loading reduces the free-volume size. Temperature-dependent PALS further confirmed the correlation between free-volume expansion and Tg. These findings establish a structure–property framework connecting nanofiller dispersion, free-volume architecture, and thermal transitions in this ternary matrix, positioning it as a candidate tunable platform for lightweight, sustainable nanocomposite films, pending complementary mechanical, electrical, and functional testing.