Electro-optical effects of oxidized multi-walled carbon nanotube doping on holographic polymer dispersed liquid crystal films

Abstract

In this work we demonstrate an improved electro-optic response and quantify the effect on transmitted wavefront properties of thiolene based reflection mode holographic polymer dispersed liquid crystals (HPDLC) gratings doped with oxidized multi-walled carbon nanotubes (MWNT). Effect of various doping levels on the reflection efficiencies is evaluated and optical spectrometry results indicate a reduction in the reflection efficiency and an anomalous electrooptic behavior at higher doping levels of MWNT especially in gratings with longer pitch where the diffusion length for liquid crystal (LC) is long. Wavefront analysis based on Shack-Hartmann wavefront sensor show an increase in the transmitted RMS wavefront error in a 633nm wavefront after a critical level of MWNT doping. Polarized optical microscopy results indicate that the MWNT do not participate in the photo polymerization induced phase separation hence acting as physical barriers for the counter diffusing LC at high MWNT concentrations. Reduction in overall size of the LC droplets in the LC rich planes, observed using scanning electron microscopy imaging, leads to faster rise and fall times hence quicker relaxation time. Observation of reduced switching voltage is attributed to the modification of dielectric properties of the medium manifested by an increase in capacitance and decrease in resistivity in presence of MWNT.