Flow alignment phenomena in liquid crystals studied by molecular dynamics simulation

Sarman, Sten; Laaksonen, Aatto

doi:10.1063/1.3238549

Cited by 13 publications

(16 citation statements)

References 42 publications

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“…Indeed, numerous equilibrium and nonequilibrium MD simulation studies of flow phenomena in bulk LC systems have been performed [19][20][21][22][23][24]. However, simulations of confined LC molecules subject to shear are less common: Simplified models of the Gay-Berne type have been considered [25,26], but, in general, to our knowledge, extensive numerical studies of LC lubricants have not been performed.…”

Section: Introductionmentioning

confidence: 99%

Boundary lubrication with a liquid crystal monolayer

et al. 2014

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We study boundary lubrication characteristics of a liquid crystal (LC) monolayer sheared between two crystalline surfaces by nonequilibrium molecular dynamics simulations, using a simplified rigid bead-necklace model of the LC molecules. We consider LC monolayers confined by surfaces with three different atomic structures, subject to different shearing velocities, thus approximating a wide variety of materials and driving conditions. The time dependence of the friction force is studied and correlated with that of the orientational order exhibited by the LC molecules, arising from the competition between the effect of the structure of the confining surfaces and that of the imposed sliding direction. We show that the observed stick-slip events for low shear rates involve order-disorder transitions, and that the LC monolayer no longer has enough time to reorder at high shear rates, resulting in a smooth sliding regime. An irregular stick-slip phase between the regular stick-slip and smooth sliding is observed for intermediate shear rates regardless of the surface structure.

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Section: Introductionmentioning

confidence: 99%

Boundary lubrication with a liquid crystal monolayer

et al. 2014

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“…Studies have also shown that the stationary alignment observed for simple one component systems may be replaced by a so called tumbling behavior for more complex materials, e.g. nematic liquid crystals with pre-transitional smectic fluctuations [10,[31][32][33], polymeric liquid crystals [34][35][36][37] as well as dilute suspensions where individual particles rotate in shear flows (Jeffery orbits, [38]). For the limiting case of very dense suspensions direct interparticle forces dominate, leading to stationary flow alignment, analogously to what is expected for simple one component systems.…”

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confidence: 99%

Orientational Order and Alignment of Elongated Particles Induced by Shear

et al. 2012

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Shear induced alignment of elongated particles is studied experimentally and numerically. We show that shear alignment of ensembles of macroscopic particles is comparable even on a quantitative level to simple molecular systems, despite the completely different types of particle interactions. We demonstrate that for dry elongated grains the preferred orientation forms a small angle with the streamlines, independent of shear rate across three decades. For a given particle shape, this angle decreases with increasing aspect ratio of the particles. The shear-induced alignment results in a considerable reduction of the effective friction of the granular material.

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“…This means that there is no orientation angle where the antisymmetric pressure is zero, so that no steady state is attained. Then the l i q u i dc r y s t a li ss a i dt ob ef l o wu n s t a b l ea n dt h ed i r e c t o rw i l lr o t a t ef o r e v e r [3, 4, 23,24].…”

Section: Shear Flow Of Nematic Liquid Crystalsmentioning

confidence: 99%

Variational Principle for Nonequilibrium Steady States Tested by Molecular Dynamics Simulation of Model Liquid Crystal Systems

Sarman¹,

Wang²,

Laaksonen³

2019

Non-Equilibrium Particle Dynamics

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The purpose of the work presented in this chapter is to test a recently proven variational principle according to which the irreversible energy dissipation rate is minimal in the linear regime of a nonequilibrium steady state. This test is carried out by performing molecular dynamics simulations of liquid crystals subject to velocity gradients and temperature gradients. Since the energy dissipation rate varies with the orientation of the director of the liquid crystal relative to these gradients and is minimal at certain orientations, this is a stringent test of the variational principle. More particularly, a nematic liquid crystal model based on the Gay-Berne potential, which can be regarded as a Lennard-Jones fluid generalized to elliptical molecular cores, is studied under planar Couette flow, planar elongational flow, and under a temperature gradient. It is found that the director of a nematic liquid crystal consisting of rod-like molecules lies in the vorticity plane at an angle of about 20°to the stream lines in the planar Couette flow. In the elongational flow, it is parallel to the elongation direction, and it is perpendicular to the temperature gradient in a heat flow. These orientations are the ones where the irreversible energy dissipation rate is minimal, so that the variational principle is fulfilled in these three cases.

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Flow alignment phenomena in liquid crystals studied by molecular dynamics simulation

Cited by 13 publications

References 42 publications

Boundary lubrication with a liquid crystal monolayer

Boundary lubrication with a liquid crystal monolayer

Orientational Order and Alignment of Elongated Particles Induced by Shear

Variational Principle for Nonequilibrium Steady States Tested by Molecular Dynamics Simulation of Model Liquid Crystal Systems

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