Order parameter and crossover temperature from temperature-dependent refractive indices for low birefringence liquid crystals

Abstract

Abstract The temperature dependencies of three low birefringence ( ∆n ) liquid crystals (LCs) at similar clearing temperatures ( T NI ) were investigated to characterize the order parameter S ( T ) and crossover temperature ( T co ). Three different methods were used to determine the S ( T ) property, including the Vuks model, the Haller approximation model, and a model based on the effective geometry parameter ( α eg ). In our low ∆n LCs with relatively analogous T NI , three parameters ( B , ( ∆n ) o , and β ) that originated from the modified four-parameter model were analyzed to increase the T co condition. A larger absolute value for the B parameter and a smaller β parameter were also needed to reduce the temperature dependence of ∆n . In particular, a lower ( ∆n ) o value was found to be beneficial for increasing the T co value, which resulted in a higher T co value for the low ∆n LCs, compared with that of a high ∆n LC with a similar T NI value. This led to a narrower temperature range between T co and T NI for the low ∆n LCs compared to that of the high ∆n LC, which could result in appropriate temperature properties for LCs for practical display applications, including a lower temperature dependence of ∆n and wider operational temperature regime.