J. Physique Lett. 44, 59-63 (1983)
DOI: 10.1051/jphyslet:0198300440205900

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

S.D. Hunnisett et J.C.A. van der Sluijs

School of Physical and Molecular Sciences, University College of North Wales, Bangor, Gwynedd LL57 2UW, Great Britain

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].

Résumé
Nous avons mesuré les propriétés visqueuses en phase nématique et isotrope du 4-cyano-4'-n-biphenyl (7-CB) par viscométrie capillaire et ultra-sonore à des fréquences comprises entre 50 et 70 MHz. En phase nématique nos résultats, comparés à ceux obtenus sous cisaillement de basse fréquence, posent d'importantes questions sur le comportement du coefficient α3 de Leslie [1, 2].

PACS
6130E - Experimental determinations of smectic, nematic, cholesteric, and lyotropic structures.
6260 - Acoustic properties of liquids.
6620 - Viscosity of liquids: diffusive momentum transport.

Key words
acoustic impedance -- nematic liquid crystals -- organic compounds -- ultrasonic propagation -- viscosity of liquids -- liquid crystal -- 4 cyano 4' n heptylbiphenyl -- viscosity -- isotropic state -- capillary viscometry -- ultrasonic shear -- 7 CB -- nematic state -- Leslie coefficient