Highly responsive reduced graphene oxide embedded PVDF flexible film-based room temperature operable humidity sensor

Abstract

The current study reports a flexible, free-standing nanocomposite thick film based on reduced graphene oxide incorporated PVDF for room temperature humidity sensing application. A facile, cost-effective solvent casting method fabricates PVDF-RGO (PR) films with varied nanofiller loadings (0.1, 0.2, and 0.3 vol%). The structural properties, including the variation in the α, β, and γ polymorphic phases, are studied in detail from XRD, FTIR, and Raman spectra, confirming the β phase’s dominance in composite films at lower RGO content. Optical studies confirm the nanofiller-induced changes in absorbance, bandgap, and Urbach energy. For films with lower RGO concentration (PR1 and PR2), a significant increase in bandgap is observed compared to pure PVDF, and the trend reverses at a higher RGO content (PR3), whereas Urbach energy has depicted an increasing trend with the filler content. Surface morphology and roughness of the film are analyzed using FESEM and AFM images, respectively. Maximum surface roughness is observed for PR3, which is one of the reasons for the exceptional humidity response of the latter sample. The compositional analysis via XPS verified the interaction between RGO and PVDF, leading to the phase transformation. The thermogram of the films manifested the increased thermal stability of composite film due to the inclusion of RGO as a nano additive. The humidity sensing measurements show that the composite films have exhibited excellent sensitivity for the relative humidity range of 11–97% compared to pure PVDF. PR3 has shown maximum sensitivity of 98.99% with a rapid dynamic response and recovery time of 21 s and 26 s, respectively. Hence, the prepared composite has revealed an outstanding humidity response in terms of sensitivity, response/ recovery time, long-term stability, and negligible hysteresis.