Temperature Dependence of Visco-Elastic Properties of 5CB

Abstract

Visco-elastic properties of 5CB as a function of temperature in the nematic region are studied. Three Miesowicz viscosity coefficients η_a η_b and η_c and rotational viscosity γ₁ are determined by dynamic light scattering (DLS) measurements. By assuming α₃ ≅ 0, other Leslie viscosity coefficients are also calculated. Fitting our γ₁ data to Osipov and Terentjev's theory, a coupling constant of 3.14k_BT_c is obtained, which is smaller than the mean field theory value. Temperature dependence of order parameter is obtained from refractive index measurement using Haller's method. To obtain accurate viscosity parameters from DLS, accurate values of elastic constants are required. Three different techniques are used to determine K₁₁, K₂₂ and K₃₃, respectively: fitting the electric field dependence of capacitance to nematic continuum theory, ac electric field DLS and magnetic Freedericksz transition.

Key Words:

• dynamic light scattering
• visco-elastic properties
• 5CB