Rheo-Optical Evidence of a Flow-Induced Isotropic−Nematic Transition in a Thermotropic Liquid-Crystalline Polymer

Mather, Patrick T.; Romo-Uribe, Ángel; Han, Chang Dae; Kim, Seung Su

doi:10.1021/ma970737h

Cited by 81 publications

(88 citation statements)

References 79 publications

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“…This birefringence (Figure 2) is the signature of the formation above the N-I transition temperature, of a non-equilibrium nematic phase oriented along the velocity axis. The first observation of shear-induced transition in the isotropic phase of thermotropic liquid crystal polymers was made by P. T. Mather in 1997 on a main-chain polymer [1]. The phenomenon was then identified a decade ago on a series of Side-Chain Liquid-Crystal Polymers (SCLCPs) evidencing the generic character of the shear-induced transition [2].…”

Section: Figurementioning

confidence: 99%

Richness of Side-Chain Liquid-Crystal Polymers: From Isotropic Phase towards the Identification of Neglected Solid-Like Properties in Liquids

et al. 2012

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Very few studies concern the isotropic phase of Side-Chain Liquid-Crystalline Polymers (SCLCPs). However, the interest for the isotropic phase appears particularly obvious in flow experiments. Unforeseen shear-induced nematic phases are revealed away from the N-I transition temperature. The non-equilibrium nematic phase in the isotropic phase of SCLCP melts challenges the conventional timescales described in theoretical approaches and reveal very long timescales, neglected until now. This spectacular behavior is the starter of the present survey that reveals long range solid-like interactions up to the sub-millimetre scale. We address the question of the origin of this solid-like property by probing more particularly the non-equilibrium behavior of a polyacrylate substituted by a nitrobiphenyl group (PANO2). The comparison with a polybutylacrylate chain of the same degree of polymerization evidences that the solid-like response is exacerbated in SCLCPs. We conclude that the liquid crystal moieties interplay as efficient elastic connectors. Finally, we show that the "solid" character can be evidenced away from the glass transition temperature in glass formers and for the first time, in purely alkane chains above their crystallization temperature. We thus have probed collective elastic effects contained not OPEN ACCESSPolymers 2012, 4 1110 only in the isotropic phase of SCLCPs, but also more generically in the liquid state of ordinary melts and of ordinary liquids.

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Section: Figurementioning

confidence: 99%

Richness of Side-Chain Liquid-Crystal Polymers: From Isotropic Phase towards the Identification of Neglected Solid-Like Properties in Liquids

et al. 2012

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“…A simple example is the existence of a tumbling phase where the molecules rotate in an applied shear [2]. Other examples include shear banding, a non-equilibrium phase separation into coexisting states with different strain rates [3], and the possibility of Williams domains, convection cells induced by an applied electric field [1].…”

Section: Introductionmentioning

confidence: 99%

Lattice Boltzmann simulations of liquid crystal hydrodynamics

2001

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We describe a lattice Boltzmann algorithm to simulate liquid crystal hydrodynamics. The equations of motion are written in terms of a tensor order parameter. This allows both the isotropic and the nematic phases to be considered. Backflow effects and the hydrodynamics of topological defects are naturally included in the simulations, as are viscoelastic properties such as shear-thinning and shear-banding. 83.70.Jr; 47.11.+j; 64.70.Md

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“…A simple closure condition for passive hard rods [46] is Q ∼ (PP) + , where A + with components A + ij = (A ij + A ji − δ ij A kk )/2 denotes the symmetric traceless part of tensor A in 2D. However, this commonly used closure condition does not account for the fact that active microswimmers permanently impose stress on the ambient fluid which feeds back into the orientational order, analogous to the shear-induced isotropicnematic transition in liquid crystals [47][48][49][50]. To derive a selfconsistent closure condition, we multiply Eq.…”

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Hydrodynamic length-scale selection in microswimmer suspensions

et al. 2016

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A universal characteristic of mesoscale turbulence in active suspensions is the emergence of a typical vortex length scale, distinctly different from the scale invariance of turbulent high-Reynolds number flows. Collective length-scale selection has been observed in bacterial fluids, endothelial tissue, and active colloids, yet the physical origins of this phenomenon remain elusive. Here, we systematically derive an effective fourth-order field theory from a generic microscopic model that allows us to predict the typical vortex size in microswimmer suspensions. Building on a self-consistent closure condition, the derivation shows that the vortex length scale is determined by the competition between local alignment forces, rotational diffusion, and intermediate-range hydrodynamic interactions. Vortex structures found in simulations of the theory agree with recent measurements in Bacillus subtilis suspensions. Moreover, our approach yields an effective viscosity enhancement (reduction), as reported experimentally for puller (pusher) microorganisms. DOI: 10.1103/PhysRevE.94.020601 A universal feature shared by many living systems is the emergence of characteristic length and time scales that arise from the nonequilibrium dynamics of their microscopic constituents. Examples range from circadian oscillations in individual cells [1] to multicellular gene-expression patterns in embryos [2] and vortex structures in microbial suspensions, endothelial tissue, and active colloids [3][4][5][6]. Yet, despite their broad biological relevance, it has proved difficult to predict quantitatively how such emergent scales arise from the underlying chemical or physical parameters. In the past decade, bacterial and other active suspensions [4,5,7] have emerged as important biophysical model systems that can help bridge the gap between large-scale spatiotemporal pattern formation and microscopic nonequilibrium dynamics [8]. At high densities, bacterial fluids form coherent vortex structures, spanning several cell lengths in diameter [5,7,9] and persisting for several seconds [9] or even minutes [10][11][12]. Although a number of insightful theoretical models have been proposed [13][14][15][16][17][18], a theory connecting microswimmer properties to the experimentally observed vortex patterns has been lacking.Here, we present such a theory by drawing guidance from the recent observation [5,9] that an effective fourth-order continuum model can provide a quantitative phenomenological description of dense bacterial suspensions [19]. This model, which combines the seminal Toner-Tu description of flocking [20] with the Swift-Hohenberg equation from pattern formation [21], describes the effective bacterial velocity field w(t,x) bywhere the bacterial pressure field q(t,x) accounts for incompressibility, ∇ · w = 0. Although a direct fit of Eq. (1) (1) directly from a generic model for polar microswimmers. The derivation specifies each parameter in the continuum theory in terms of microscopic swimmer parameters and yields direct theoretical ...

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Rheo-Optical Evidence of a Flow-Induced Isotropic−Nematic Transition in a Thermotropic Liquid-Crystalline Polymer

Cited by 81 publications

References 79 publications

Richness of Side-Chain Liquid-Crystal Polymers: From Isotropic Phase towards the Identification of Neglected Solid-Like Properties in Liquids

Richness of Side-Chain Liquid-Crystal Polymers: From Isotropic Phase towards the Identification of Neglected Solid-Like Properties in Liquids

Lattice Boltzmann simulations of liquid crystal hydrodynamics

Hydrodynamic length-scale selection in microswimmer suspensions

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