J. Physique Lett. 46, 881-886 (1985)
DOI: 10.1051/jphyslet:019850046018088100

A new torsion pendulum technique to measure the twist elastic constant of liquid crystals

S. Faetti, M. Gatti et V. Palleschi

Dipartimento di Fisica dell'Universita' di Pisa, Piazza Torricelli 2, 56100 Pisa, Italy

Abstract
A new experimental method to measure the twist elastic constant of nematic liquid crystals is proposed. The method is based on a direct measurement of the torque which the nematic liquid crystal exerts on the surfaces when a magnetic field is applied. The reliability of this technique is tested by measuring the twist elastic constant of the nematic liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB). The experimental results are compared with previous measurements performed by other authors.

Résumé
Une nouvelle technique de mesure de la constante élastique de torsion des cristaux liquides nématiques est proposée. Cette technique est basée sur une mesure directe du couple exercé par le directeur sur les surfaces quand le nématique est soumis à un champ magnétique. Cette technique est appliquée à la mesure de la constante élastique K22 du cristal liquide 4-n-pentyl-4'-cyanobiphényl (5CB).

PACS
6130G - Orientational order of liquid crystals in electric and magnetic fields.
6210 - Mechanical properties of liquids.

Key words
elastic constants -- nematic liquid crystals -- organic compounds -- torsion -- 5CB -- torsion pendulum technique -- twist elastic constant -- nematic liquid crystals -- magnetic field -- 4 n pentyl 4' cyano biphenyl