Viscoelasticity in Liquid Crystals Studied by Dynamic Light Scattering

In part because of its anticipated application for faster and lower power-consuming electro-optic devices and low operating voltage in multicolor LC display, the bent-core nematic (BCN) liquid crystals has long been sought after. The viscoelastic parameters are relevant to performance of LC devices and to the understanding of the connection between unusual properties and structure that gives rise to them. We have investigated the viscoelastic properties in the nematic phases of three BCNs, using dynamic light scattering (DLS) and magnetic Fredericksz transition on well aligned samples. Our results reveal unusual viscoelastic parameters with very large orientational viscosities compared to conventional rod-like calamitic LCs, which is discussed in terms of a nematic containing molecular clusters exhibiting short-range smectic-CP-type correlations. We have conducted additional DLS studies on one of these three BCNs to search for fluctuation modes that are not purely associated with the uniaxial director. We have analyzed our results using available models – including formation of short-range smectic layered clusters – used to describe the microscopic structure of bent-core nematics.