Ultrasonic shear and 'capillary viscosity study of 4-cyano-4'-n-heptylbiphenyl in the nematic and the isotropic state

Abstract

Using capillary viscometry and ultrasonic shear at frequencies between 50 and 70 MHz, we have measured viscous properties of 4-cyano-4'-n-biphenyl (7-CB) in the nematic and the isotropic state. The data in the nematic state, when compared with results from low frequency shear experiments, raise important questions on the behaviour of the Leslie coefficient α3 [1, 2]

Transient flow-driven distortion of a nematic liquid crystal in channel flow with dissipative weak planar anchoring

“…For nematic materials that are commonly used in industrial manufacturing of LCDs, typically is small. For example, 0.210 for 4-Cyano-4'-pentylbiphenyl (5CB) [17], 0.143 for 4-Cyano-4'-heptylbihenyl (7CB) [48], and 0.001 for 4-Cyano-4'-octyloxybiphenyl (8OCB) [49]. In fact, most modern LCDs use mixtures of nematics with physical properties similar to E7, which contains 51% 5CB, 25% 7CB, 16% 8OCB and 8% of other similar biphenyl compounds [50], and so typically is also small for these mixtures.…”

“…The insets inFigure 4show the corresponding results for an intermediate value ofĒr, namelyĒr = 50. In particular,Figure 4shows how the leading-order velocity in the channel u 0 given by(48) affects both the initial director angle and the steady state director angle. Specifically, as described in Section II C, in the lower half of the channel the positive shear rate (∂u 0 /∂z > 0) rotates the director angle towards the positive Leslie angle φ 1 = +1, while in the upper half of the channel the negative shear rate (∂u 0 /∂z < 0) rotates it towards the negative Leslie angle φ 1 = −1.…”