Determination of viscoelastic coefficients from the optical transmission of a planar liquid crystal cell with low-frequency modulated voltage

Abstract

The viscoelastic response of the nematic director field to low-frequency modulations of the driving voltage was studied by means of optical transmission measurements. An external ac voltage above the critical field Uc was weakly amplitude modulated with frequencies in the range of 1 to 100Hz. The viscosity coefficients a 1 , r 11 r 2 , and 'Tfb influence the time dependence of the director field. They were determined by fitting the phase and amplitude of theoretically calculated optical transmission curves to measured data.

Nematic Liquid Crystals: Physical Properties, Section 2.5

“…tial law. The relaxation of the deformation angle @between the director orientation in the sample and at the surface is given by (39) 2 (40) z -I / l a -Yl n2k22 ~~a~c 2…”

Experimental Determination of Elastic and Viscous Parameters of Liquid Crystals

“…Moreover, the light intensity shows nonmonotonic dependence on d in accordance with (5.40). Attempts to extract other Leslie coefficients [112] provided numerical values of low accuracy that can be used only for estimations. In principle, this procedure can help determine almost all Leslie coefficients at strong deformation of the initial structure under electric field [112].…”

“…46 Temperature dependence of g 1 (T) for MBBA obtained from the experiments in geometry with initial planar (P) and homeotropic (H) orientation. (After Schmiedel et al[112]. (After Schmiedel et al[112].…”

Influence of surface anchoring and viscosity upon the switching behavior of twisted nematic cells

“…13 -15 The bulk viscosities are measurable using a lowfrequency modulation method. 16 An offset voltage is modulated in the frequency range of 1-100 Hertz and the time dependence of the optical transmission is measured. From this, a phase difference between voltage and transmission is obtained.…”