Synthesis-temperature-driven evolution of structural, optical and charge transport properties in polypyrrole–poly(vinyl alcohol) nanocomposites

This study presents a systematic investigation of the influence of synthesis temperature on the structural, optical and charge transport properties of polypyrrole–polyvinyl alcohol (PPy–PVA) nanocomposites prepared by in situ dispersion polymerisation. Films synthesised at 5°C, 25°C and 50°C were characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, UV–Visible absorption spectroscopy and electrical transport measurements. SEM analysis reveals predominantly spherical nanoparticles with mean diameters of 50 ± 5 nm, 75 ± 6 nm and 92 ± 7 nm at 5, 25 and 50°C, respectively. The resolved PPy-related diffraction feature becomes progressively sharper with increasing synthesis temperature, and the apparent crystallite size increases from 5.8 ± 0.5 nm for Film 2 to 8.7 ± 0.6 nm for Film 3. FTIR analysis indicates interactions between the PPy and PVA components, with changes in the hydroxyl-related spectral features suggesting the involvement of Fe³⁺-mediated coordination. Tauc plot analysis yields optical band gaps of 2.08 ± 0.03 eV, 1.82 ± 0.03 eV and 1.72 ± 0.03 eV, decreasing monotonically with synthesis temperature. Room-temperature in-plane conductivity increases correspondingly from (5.6 ± 0.4) × 10⁻² S cm⁻¹ to (19.1 ± 0.8) × 10⁻² S cm⁻¹. Statistical analysis of temperature-dependent conductivity using Mott's variable-range hopping (VRH) model reveals a transition in charge transport dimensionality from two-dimensional (2D) VRH at 5°C to three-dimensional (3D) VRH at 25°C and 50°C. These results establish a coherent, quantitative correlation among synthesis temperature, nanoparticle morphology, crystallite size, optical band gap, DC conductivity and hopping dimensionality, underscoring the potential of PPy–PVA nanocomposites for flexible electronics, optoelectronic devices and chemical sensing.