Studies on Thin Films of Hexa-Alkoxy Triphenylene(HAT5) and Composite of HAT5-TiO2 Nanoparticles

Abstract

The studies on discotic liquid crystals are important not only for basic scientific research but also for industrial applications. It can be potentially employed for the fabrication of devices in photovoltaics, organic solar cells and organic LEDs. Hexa-alkoxy triphenylene (HAT5) is one of the commonly studied discotic liquid crystals. We formed Langmuir monolayer of pure HAT5 on ultrapure water subphase. We have studied the effect of doping the monolayer of HAT5 with different concentration of TiO2 nanoparticles on the surface pressure-area isotherms of the Langmuir monolayer. We observed considerable shift in the isotherms towards lower area per molecule on increasing the concentration of TiO2. We deposited the Langmuir-Blodgett (LB) films of pure HAT5 and HAT5+TiO2 (5 and 20% by weight) nanocomposites on the glass substrates. We characterized the films using UV-Vis spectrophotometer and atomic force microscope (AFM). The energy gap is found to decrease with increasing concentration of TiO2 nanoparticles in the HAT5 matrix. It decreases rapidly with increasing the target surface pressure of LB deposition. The AFM images reveal higher density of clusters of TiO2 nanoparticles with the increase in concentration of the nanoparticles in HAT5 monolayer. Such increase in the density may results in reduction in energy gap of the LB films of the nanocomposites.