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Crystals 2019, 9(3), 143; https://doi.org/10.3390/cryst9030143

Effect of Size Polydispersity on the Pitch of Nanorod Cholesterics

Laboratoire de Physique des Solides—UMR 8502, CNRS, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay, France
Received: 13 February 2019 / Revised: 4 March 2019 / Accepted: 4 March 2019 / Published: 10 March 2019
(This article belongs to the Special Issue Advances in Cholesteric Liquid Crystals)
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Abstract

Many nanoparticle-based chiral liquid crystals are composed of polydisperse rod-shaped particles with considerable spread in size or shape, affecting the mesoscale chiral properties in, as yet, unknown ways. Using an algebraic interpretation of Onsager-Straley theory for twisted nematics, we investigate the role of length polydispersity on the pitch of nanorod-based cholesterics with a continuous length polydispersity, and find that polydispersity enhances the twist elastic modulus, K 2 , of the cholesteric material without affecting the effective helical amplitude, K t . In addition, for the infinitely large average aspect ratios considered here, the dependence of the pitch on the overall rod concentration is completely unaffected by polydispersity. For a given concentration, the increase in twist elastic modulus (and reduction of the helical twist) may be up to 50% for strong size polydispersity, irrespective of the shape of the unimodal length distribution. We also demonstrate that the twist reduction is reinforced in bimodal distributions, obtained by doping a polydisperse cholesteric with very long rods. Finally, we identify a subtle, non-monotonic change of the pitch across the isotropic-cholesteric biphasic region. View Full-Text
Keywords: chirality; cholesterics; nanorods; Onsager theory; polydispersity chirality; cholesterics; nanorods; Onsager theory; polydispersity
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Wensink, H.H. Effect of Size Polydispersity on the Pitch of Nanorod Cholesterics. Crystals 2019, 9, 143.

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