Indium tin oxide nanoparticles induced tunable dual alignment in nematic liquid crystal

Abstract

Monotonic alignment variation with a uniaxial domain through the noncontact-based technique is highly appreciated for several elements of LC-based latest technologies (that rely on the alignment of LC molecules over the desired substrate). So, with this motivation, the present article covers the achievement of various alignments (homogeneous and homeotropic) of a nematic liquid crystal (NLC, 5CB) material in ITO sample cell devoid of alignment layer by dispersion of indium tin oxide (ITO) NPs (0.25 wt% and 1 wt%). Firstly, various LC alignments are observed with the help of polarizing optical micrographs (POM) in presence of external DC biasing voltage (ranging from 5 to 20 V) at 28˚C. POM depicts the various domains of 5CB in pristine form while uniform vertical (homeotropic) monodomain was achieved through the dispersion of 0.25 wt% ITO NPs that, interestingly, again tuned to the planar (homogeneous) alignment when ITO concentration was increased up to 1 wt%. The achievement of tunability in the alignments may be attributed to the ITO-ITO interaction and their various arrangements on the ITO substrate. Moreover, conoscopic study done on this composite also confirmed the uniform mono-domain vertical alignment under cross polarizers. To further confirm POM observations, the frequency-bias dependent dielectric parameters (dielectric permittivity, dielectric loss and loss factor) were also examined that eventually confirming the vertical alignment only for 0.25 wt% ITO NPs-5CB composite. We do anticipate that the underlying mechanism of ITO NPs based on the tunable dual alignment could be utilized to make improved and high-performance tunable LC-based devices.