Shear-stress-controlled dynamics of nematic complex fluids

Klapp, Sabine H. L.; Hess, Siegfried

doi:10.1103/physreve.81.051711

Cited by 13 publications

(19 citation statements)

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“…Fd-virus has been extensively used for fundamental studies during the last few decades [1,2], as their high aspect-ratio and mono-dispersity makes them a quasi-ideal system for investigating the equilibrium [3,4] and the out-of-equilibrium behavior [5,6,7,8,9] of rod-like colloids. It has been used, for example, to test the theoretically-predicted dynamical transitions in sheared nematics [10,11,12]. For those systems, indeed, a quantitative comparison with simulations [13] and theory [14] was found.…”

Section: Introductionmentioning

confidence: 99%

The Connection between Biaxial Orientation and Shear Thinning for Quasi-Ideal Rods

et al. 2016

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Abstract:The complete orientational ordering tensor of quasi-ideal colloidal rods is obtained as a function of shear rate by performing rheo-SANS (rheology with small angle neutron scattering) measurements on isotropic fd-virus suspensions in the two relevant scattering planes, the flow-gradient (1-2) and the flow-vorticity (1-3) plane. Microscopic ordering can be identified as the origin of the observed shear thinning. A qualitative description of the rheological response by Smoluchowski, as well as Doi-Edwards-Kuzuu theory is possible, as we obtain a master curve for different concentrations, scaling the shear rate with the apparent collective rotational diffusion coefficient. However, the observation suggests that the interdependence of ordering and shear thinning at small shear rates is stronger than predicted. The extracted zero-shear viscosity matches the concentration dependence of the self-diffusion of rods in semi-dilute solutions, while the director tilts close towards the flow direction already at very low shear rates. In contrast, we observe a smaller dependence on the shear rate in the overall ordering at high shear rates, as well as an ever-increasing biaxiality.

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Section: Introductionmentioning

confidence: 99%

The Connection between Biaxial Orientation and Shear Thinning for Quasi-Ideal Rods

et al. 2016

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“…As a result, the rotation occurs in both directions. Some rotation cycles are completed (180 • ), and some change direction before such that the appearance of rheochaos (chaotic stress-strain curves and/or orientational dynamics [21]) is to be expected. Incomplete rotations in the flow-gradient plane are known as wagging such that we could call this behavior helicopter-wagging.…”

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Helicopter rotation and smectic-isotropic coexistence of strongly attractive rods

Ripoll

2011

Phys. Rev. E

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Hydrodynamic simulations of strongly attractive rodlike colloids are performed with and without shear flow. In the absence of flow, the isotropic-nematic coexistence becomes isotropic-smectic A, and the interfacial properties clearly vary with increasing attraction strength. In the presence of shear flow, a new collective rotation appears in which the director rotates in the vorticity-flow plane in a similar fashion to the movement of the rotor of a helicopter. DOI: 10.1103/PhysRevE.83.040701 PACS number(s): 64.70.M−, 82.70.Dd, 64.60.−i, 83.50.−v Liquid crystals in equilibrium, and in the presence of flow fields, show a very rich structural and dynamical behavior. Equilibrium phase diagrams display coexistence between isotropic (I), where rods are randomly oriented, nematic (N), where rods have a orientational preference, smectic (Sm), with both orientational and positional order, and crystalline phases, where the positional order is long ranged [1]. Attraction induced by depletion interactions has been considered in analytical calculations and experiments [2,3] of rods with large aspect ratios (rod length L over rod diameter σ ). The broadening of existing coexistence regions like I-N and N-Sm has been determined, together with the appearance of new ones as I-I, N-N, and eventually also I-Sm. Computer simulations are a powerful tool that can provide a detailed description of these systems. Numerous simulations with repulsive rods of small aspect ratios, typically from 2 to 6, have studied phases with positional order (see, e.g., Ref.[4]). Simulations of thermotropic systems of Gay-Berne colloidal rods [5] with increasing attraction have reported the appearance of different phases as a function of the potential asymmetry. Gay-Berne forces become unrealistically thin at the ends with increasing aspect ratio. I-Sm coexistence has been obtained with such rods by keeping the two phases at different temperatures [6]. In the presence of shear flow, the phase diagram is fundamentally altered [7]. Isotropic phases tend to align with flow, and oriented phases may undergo orchestrated motions that have been characterized about two decades ago [8]. Nematic phases have shown rotations in the flow-gradient plane (similar to the blades of a mill) or with an angle tilted in the vorticity direction (similar to the paddle in a kayak). These rotations are known as tumbling and kayaking [9]. Emerging questions are the effect that shear has when interfaces of varying softness are present or when applied to phases with positional order. Examples of attractive colloids where shear alignment is interesting for industrial applications are carbon nanotubes [10], wormlike micelles [11], or polymers.In this Rapid Communication, we investigate by means of computer simulations the effect of large attractions on the I-N coexistence of systems of rods with aspect ratio 20. At rest, increasing the attraction transforms the nematic phase into the smectic and linearly decreases the interface width. In the presence of shear flow, a qualitativ...

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“…In nonlinear dynamics it typically refers to anisochronicity, i.e., the dependence of the frequency of oscillations on their amplitude [43]. In fluid dynamics a similar principle is known as shear: any real fluids moving along a solid boundary will incur a shear stress at that boundary [44]. In the laser community the term amplitude-phase coupling defines a concept which implies that the phase of the electric field inside the laser cavity is dynamically linked to its amplitude.…”

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Amplitude-phase coupling drives chimera states in globally coupled laser networks

et al. 2015

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For a globally coupled network of semiconductor lasers with delayed optical feedback, we demonstrate the existence of chimera states. The domains of coherence and incoherence that are typical for chimera states are found to exist for the amplitude, phase, and inversion of the coupled lasers. These chimera states defy several of the previously established existence criteria. While chimera states in phase oscillators generally demand nonlocal coupling, large system sizes, and specially prepared initial conditions, we find chimera states that are stable for global coupling in a network of only four coupled lasers for random initial conditions. The existence is linked to a regime of multistability between the synchronous steady state and asynchronous periodic solutions. We show that amplitude-phase coupling, a concept common in different fields, is necessary for the formation of the chimera states. Synchronization is a common phenomenon in interacting nonlinear dynamical systems in various fields of research such as physics, chemistry, biology, engineering, or socioeconomic sciences [1][2][3]. While a lot of knowledge has been gained on the origin of complete synchronization, more complex partial synchronization patterns have only recently become the focus of intense research. We still lack a full understanding of these phenomena, and a very prominent example are chimera states where an ensemble of identical elements self-organizes into spatially separated coexisting domains of coherent (synchronized) and incoherent (desynchronized) dynamics [4,5]. Since their first discovery a decade ago many theoretical investigations of coupled phase oscillators and other simplified models have been carried out [6,7] [7,16,17], e.g., spiral wave chimeras [18,19], FitzHugh-Nagumo neural systems [20], Stuart-Landau oscillators [21][22][23], where pure amplitude chimeras [24] were found, or quantum interference devices [25]. In real-world systems chimera states might play a role, e.g., in the unihemispheric sleep of birds and dolphins [26], in neuronal bump states [27,28], in power grids [29], or in social systems [30].Although no universal mechanism for the formation of chimera states has yet been established, three general essential requirements have been found in many studies: (i) a large number of coupled elements, (ii) non-local coupling, and (iii) specific initial conditions. These were primarily derived from the phase oscillator model [7] but also apply to other systems. If these conditions are not met, the chimera states tend to have very short lifetimes. Recent studies, however, suggest that these paradigms can be broken and chimera states are observed also for small system sizes [31], global coupling [15,23,32,33] and random initial conditions [34].Surprisingly, chimera states appear at the interface of independent fields of research putting together different scientific communities. Recent examples are quantum chimera state [35] or coexistence of coherent and incoherent patterns with respect to the modes of an optical com...

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Shear-stress-controlled dynamics of nematic complex fluids

Cited by 13 publications

References 58 publications

The Connection between Biaxial Orientation and Shear Thinning for Quasi-Ideal Rods

The Connection between Biaxial Orientation and Shear Thinning for Quasi-Ideal Rods

Helicopter rotation and smectic-isotropic coexistence of strongly attractive rods

Amplitude-phase coupling drives chimera states in globally coupled laser networks

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