Optical and thermo-optical properties of polyvinyl alcohol/carbon nanotubes composites investigated by prism coupling technique

Abstract

In this paper, optically tunable polyvinyl alcohol (PVA) nanocomposite films containing carboxyl functionalized multi-walled carbon nanotubes (COOH-MWCNT) were developed using the solution casting method. The compositional dependence on morphological, structural, optical, and thermo-optical properties of these nanocomposites was studied using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and prism coupling measurements. It was be found that a small loading with MWCNT affects the molecular mobility of PVA/MWCNT nanocomposites and results in prominent modifications of their optical and thermo-optical properties. The incorporation of 0.1 wt% harms improving PVA's refractive characteristics, whereas with nanotubes content in the range of 0.1–1 wt%, the refractive index increases. The refractive indices were measured at different wavelengths (from 404 to 1548 nm) and the dispersion coefficients were calculated. The temperature dependence of the refractive index of PVA nanocomposites in the temperature range from 30 °C to 110 °C was also explored and the thermo-optic coefficients were determined. The measured thermo-optic coefficients (dn/dT) were found to be negative below the glass transition temperature and on the order of 10−4/°C. Furthermore, dn/dT decreases with the thermal expansion coefficient and increases with the MWCNT weight fraction. The promising results suggest an enormous potential of PVA/MWCNT composites for use in tunable optical devices.