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Memory Effects in Randomly Perturbed Nematic Liquid Crystals

Authors: Amid Ranjkesh, Milan Ambrožič, Samo Kralj

Abstract:

We study the typical domain size and configuration character of a randomly perturbed system exhibiting continuous symmetry breaking. As a model system we use rod-like objects within a cubic lattice interacting via a Lebwohl–Lasher-type interaction. We describe their local direction with a headless unit director field. An example of such systems represents nematic LC or nanotubes. We further introduce impurities of concentration p, which impose the random anisotropy field-type disorder to directors. We study the domain-type pattern of molecules as a function of p, anchoring strength w between a neighboring director and impurity, temperature, history of samples. In simulations we quenched the directors either from the random or homogeneous initial configuration. Our results show that a history of system strongly influences: i) the average domain coherence length; and ii) the range of ordering in the system. In the random case the obtained order is always short ranged (SR). On the contrary, in the homogeneous case, SR is obtained only for strong enough anchoring and large enough concentration p. In other cases, the ordering is either of quasi long range (QLR) or of long range (LR). We further studied memory effects for the random initial configuration. With increasing external ordering field B either QLR or LR is realized.

Keywords: Liquid crystals, disorder, memory effect, Lebwohl-Lasher model, orientational order

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1070825

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References:


[1] ZurekW.H."Cosmological experiments in superfluid helium?" Nature, 1985, 317, 505.
[2] Bray A.J. "Theory of phase-ordering kinetics" Adv. Phys. 1994,43, 357.
[3] Kibble T.W.B. "Topology of cosmic domains and strings "J. Phys. A: Math.Gen., 1976, 9, 1387,.
[4] Imry Y.; Ma S. "Random-Field Instability of the Ordered State of ContinuousSymmetry"Phys. Rev. Lett., 1975,35, 1399.
[5] Feldman D.E. "Quasi-long-range order in nematics confined in random porous media"Phys. Rev. Lett., 2000,85, 4886.
[6] ChakrabartiJ. Phys. Rev. Lett. 1998, 81, 385.
[7] Cleaver D.J.; Kralj S.; Sluckin T.J.; Allen M P.In Liquid Crystals in "Complex Geometries Formed by Polymer and Porous Networks" Crawford G.P. and Zumer S. Eds.; Oxford University Press: London, 1996.
[8] Radzihovsky L. Toner "Anomalous Elasticity of Disordered Smectics"J.Phys. Rev. Lett., 1997,79, 4214.
[9] Popa-Nita V. " " Statics and Kinetics at the Nematic-Isotropic Interface in Porous Media"" Eur. Phys. J., 1999, 83, 12.
[10] Popa-Nita V.; Romano S. " Nematic-Smectic A Phase Transition in Porous Media" Chem. Phys., 2001,91, 264.
[11] De Gennes P.G.; Prost J. "The Physics of LiquidCrystals" Oxford University Press: Oxford, 1993.
[12] Virga E.G. Variational "Theories for Liquid Crystals" Chapman Hall: London, 1994.
[13] M.Ambrožic,S.Kral,E.G.Virga"Defect-enhanced nematic surface order reconstruction" , Phys. Rev. E , 2007,75, 031708 .
[14] M.Ambrožic S. Kralj,T.J.Sluckin, S. Žumer, and D. Sven┼íek "Annihilation of edge dislocations in smectic-A liquid crystals" Phys. Rev. E , 2004,70, 051704 .
[15] Lebwohl P.A.; Lasher G. "Nematic-Liquid-Crystal OrderÔÇöA Monte Carlo Calculation", Phys. Rev. A, 1972, 6, 42.
[16] M.Krasna, M.Cvetko, M. Ambrozic1 "Symmetry breaking and structure of a mixture of nematic liquid crystals and anisotropic nanoparticles",Beilstein J. Org. Chem.6, No. 74,2010.
[17] Cruz, C.; Figueirinhas, J. L.; Filip, D.; Feio, G.; Ribeiro, A. C Frère, Y.;Meyer, T.; Mehl, G. H. "Biaxial nematic order and biaxial order and phase behavior studies in an organosiloxanetetrapode using complementary deuterium NMR experiments" Phys. Rev. E, 2008,78,051702.
[18] Popa-Nita, V."Statics and kinetics at the nematic-isotropic interface in porous media" Eur. Phys. J. B, 1999,12, 83-90.
[19] Popa-Nita, V.; Gerli─ì, I.; Kralj, S. Int. "The Influence of Disorder on ThermotropicNematic Liquid Crystals Phase Behavior" J. Mol. Sci. , 10(9), 2009,3971-4008.
[20] Romano, S. Int. J. Mod. Phys. B " Computer simulation study of a Nematogenic Lattice-Gas model with fourth- rank interactions ", 2002,16,2901-2915.