Thermodynamic and spectroscopic characterization of a weakly polar liquid crystalline compound dispersed with polyvinyl pyrrolidone capped gold nanoparticles

Abstract

In the present study a deliberate attempt has been made to examine the consequences of dispersion of gold nanoparticles in an azoxybenzene-based nematic liquid crystal, namely 4,4′- di pentyl azoxy benzene. Investigations were made on gold nanoparticles doped nematic liquid crystals analysing differential scanning calorimetry, polarized light microscopy, ultraviolet–visible absorption spectroscopy, photoluminescence and Fourier-transform infrared spectroscopy (FTIR). Gold nanoparticles of different concentrations 0.25, 0.5, and 1.0 wt% were dispersed in pure 4,4′- di pentyl azoxy benzene, and it was observed in the experiment that no significant change occurs in the crystal to nematic phase (Cr-Ne) transition temperature with the increase in gold nanoparticles concentration. However, the nematic to isotropic (Ne-Iso) transition temperature decreases significantly with the increase in gold nanoparticles concentration. This study reports around 76% increase in ultraviolet–visible absorbance and 46% enhancement of photoluminescence intensity with the suitable amount of gold nanoparticles dispersion in 4,4′- di pentyl azoxy benzene. The surface plasmonic resonance (SPR) and re-excitation of 4,4′- di pentyl azoxy benzene molecule due to collision with gold nanoparticles has been accredited to the escalation in photoluminescence intensities.