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Soft Matter and Biological Physics

Eur. Phys. J. E 4, 21-28

Cellular solid behaviour of liquid crystal colloids 2. Mechanical properties

V.J. Anderson and E.M. Terentjev.

Cavendish Laboratory, The University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK


(Received 13 March 2000 and Received in final form 6 June 2000)

This paper presents the results of a rheological study of thermotropic nematic colloids aggregated into cellular structures. Small sterically stabilised PMMA particles dispersed in a liquid crystal matrix densely pack on cell interfaces, but reversibly mix with the matrix when the system is heated above $T_{\rm ni}$. We obtain a remarkably high elastic modulus, $G'
\geq 10^5 {Pa}$, which is a nearly linear function of particle concentration. A characteristic yield stress is required to disrupt the continuity of cellular structure and liquify the response. The colloid aggregation in a "poor nematic"MBBA has the same cellular morphology as in the "good nematic"5CB, but the elastic strength is at least an order of magnitude lower. These findings are supported by theoretical arguments based on the high surface tension interfaces of a foam-like cellular system, taking into account the local melting of nematic liquid and the depletion locking of packed particles on interfaces.

61.30.-v - Liquid crystals..
82.70.-y - Disperse systems..
81.40.Jj - Elasticity and anelasticity, stress-strain relations..

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001