Temperature dependence of visco-elastic properties of 5CB

Visco-elastic properties of 5CB as a function of temperature in the nematic region are studied. Three Miesowicz viscosity coefficients eta(a), eta(b) and eta(c) and rotational viscosity gamma(1) are determined by dynamic ligh t scattering (DLS) measurements. By assuming alpha(3) = 0, other Leslie vis cosity coefficients are also calculated. Fitting our gamma(1) data to Osipo v and Terentjev's theory, a coupling constant of 3.14k(B)T(c) is obtained, which is smaller than the mean field theory value. Temperature dependence o f order parameter is obtained from refractive index measurement: using Hall er's method. To obtain accurate viscosity parameters from DLS, accurate val ues of elastic constants are required. Three different techniques are used to determine K-11, K-22 and K-33, respectively: fitting the electric field dependence of capacitance to nematic continuum theory, ac electric field DL S and magnetic Freedericksz transition.