Effect of cetyltrimethylammonium bromide coatings on indium tin oxide surfaces in reverse mode polymer dispersed liquid crystal films

Abstract

The vertical alignment of liquid crystals (LCs) on cetyltrimethylammonium bromide-coated (CTAB-coated)indium tin oxide (ITO) glass is the consequence of specific interactions between the LCs, CTAB and ITO surface. The CTAB concentration influences the LC orientation, which changes the ITO surface energy. Changes in the surface energy of CTAB-coated ITO glass are investigated by the Owens–Wendt method. Both polar- and dispersive-component energies on the ITO surface decrease as the CTAB concentration increases, and reach saturation around 0.002% CTAB. The physico-chemical interaction between the LCs and the ITO surface was diminished by the presence of the CTAB layer, which induced the vertical alignment of LCs having positive or negative dielectric anisotropy. Vertical alignment is confirmed using crossed polarisers and the crystal rotation method. The electro-optical properties of fabricated reverse mode polymer dispersed liquid crystal films display transmittance of Ton: 29.7%, Toff: 85% and a response time of τon: 33 ms, τoff: 107 ms.