Effect of Silica on Director Alignment of 4-cyano-4’pentylbiphenyl Liquid Crystal

Abstract

The application of liquid crystal can be look so advanced nowadays in the evolution of liquid crystal displays (LCDs).In this study, colloidal particles of silica, SiO2 were dispersed in the liquid crystal, 4-cyano-4‟-
pentylbiphenyl (5CB) during isotropic phase. Various sets of SiO2 with different concentrations were prepared from 1 to 5 w/v%. The phase behaviour and morphologies of this silica colloidal liquid crystal were characterized by three different techniques, which are infrared spectroscopy (IR), polarized optical microscopy (POM) and electron spin resonance (ESR). The IR spectra revealed the presence of functional groups in the compounds indicating there are no chemical changes in which only physical interactions were involved when two different compounds were mixed together. The POM characterization was used to determine the presence of birefringence and the temperature of phase transition of liquid crystal and its hybrid system. The result showed the hybrid system exhibits nematic phase upon temperature at 25.0 °C. The ESR technique able to determine the director alignment of liquid crystal where it shows the director is affected by the silica concentration. The suspension of liquid crystal with low concentration of silica, 1 w/v% was found to align the director of liquid crystal in between of parallel and perpendicular to the magnetic field. By increasing the concentration of silica up to 5 w/v%, powder pattern was
finally observed.