Simulations of liquid crystals in Poiseuille flow

Denniston, Colin; Orlandini, Enzo; Yeomans, J. M.

doi:10.1016/s1089-3156(01)00004-6

Cited by 32 publications

(33 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We confirm the transition reported by Denniston et al 18 and Jewell et al 19 , and find that it is driven by a dynamical instability, rather than free energy considerations. We also observe a very strong departure from the Poiseuille relation that does not relate to any obvious morphological transition.…”

Section: Introductionsupporting

confidence: 92%

“…2, typically changes discontinuously at the transition, with a decrease in the free energy observed for all measured values ofα except α = ∞. This contradicts the explanation of Jewell et al 19 that the transition occurs at the point where the free energies of the two textures are equal, and supports the observation of Denniston et al 18 that V can persist as a metastable state; we find that it does so until driven into the H state by the dynamical instability. Theα = ∞ case shows an increase in free energy, indicating that the V state becomes dynamically unstable before any free energy crossover with H occurs.…”

Section: The Next Order Velocity Equation Iscontrasting

confidence: 69%

“…Again following Jewell et al 19 we term this new state the horizontal state, H. The change V → H represents a topological change and cannot be effected by continuous deformations. As noted by Denniston et al 18 , the transition occurs by the formation of topological defects, which unwind to produce the new state. Intriguingly, the transition only causes a small discontinuity in the dependence of Φ onG, barely noticeable in comparison to the jump described in the previous two paragraphs.…”

Section: Homeotropic Anchoringmentioning

confidence: 90%

See 2 more Smart Citations

The effect of anchoring on the nematic flow in channels

2015

View full text Add to dashboard Cite

Understanding the flow of liquid crystals in microfluidic environments plays an important role in many fields, including device design and microbiology. We perform hybrid lattice-Boltzmann simulations of a nematic liquid crystal flowing under an applied pressure gradient in two-dimensional channels with various anchoring boundary conditions at the substrate walls. We investigate the relation between flow rate and pressure gradient and the corresponding profile of the nematic director, and find significant departures from the linear Poiseuille relation. We also identify a morphological transition in the director profile and explain this in terms of an instability in the dynamical equations. We examine the qualitative and quantitative effects of changing the type and strength of the anchoring. Understanding such effects may provide a useful means of quantifying the anchoring of a substrate by measuring its flow properties.

show abstract

Section: Introductionsupporting

confidence: 92%

Section: The Next Order Velocity Equation Iscontrasting

confidence: 69%

Section: Homeotropic Anchoringmentioning

confidence: 90%

See 1 more Smart Citation

The effect of anchoring on the nematic flow in channels

2015

View full text Add to dashboard Cite

show abstract

“…Explorations beyond this Poiseuilledetermined regime could open new microfluidic phenomena and applications [218,219]. Although experimental investigations of complex fluids in microfluidic confinements have been initiated [31,38,39,220,221], understanding of their dynamics is mostly limited to numerical studies [222][223][224][225][226][227][228]. In particular, investigations on liquid crystals as a natural choice for an anisotropic replacement of the isotropic fluids have been directed towards effects mediated by topological defects [24,60,114,121,192,[229][230][231].…”

Section: Nematic Flow In a Homeotropic Microchannelmentioning

confidence: 99%

“…The numerical modeling (carried out by Miha Ravnik) was based on solving the BerisEdwards model of nematofluidics with the hybrid lattice Boltzmann algorithm complements the experiments [223,224]. Fluorescence confocal signal intensity I was calculated from the local director n i and laser polarization P i as I ∝ (n i P i ) 4 , and the POM micrographs were calculated with the Jones 2 × 2 matrix formalism [194].…”

Section: Tunable Flow Shapingmentioning

confidence: 99%

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Sengupta

Herminghaus

Bahr

2011

Molecular Crystals and Liquid Crystals

View full text Add to dashboard Cite

Where the mind is without fear and the head is held high;Where knowledge is free;Where the world has not been broken up into fragments by narrow domestic walls;Where words come out from the depth of truth;Where tireless striving stretches its arms towards perfection;Where the clear stream of reason has not lost its way into the dreary desert sand of dead habit;Where the mind is led forward by thee into ever-widening thought and actionInto that heaven of freedom, my Father, let my country awake.Rabindranath Tagore (1861Tagore ( -1941 To my parents, my brother, and all the sacrifices they made for me AbstractThe doctoral thesis presented here is one of the first systematic attempts to unravel the wonderful world of liquid crystals within microfluidic confinements, typically channels with dimensions of tens of micrometers. The present work is based on experiments with a roomtemperature nematic liquid crystal, 5CB, and its colloidal dispersions within microfluidic devices of rectangular cross-section, fabricated using standard techniques of soft lithography. To begin with, a combination of physical and chemical methods was employed to create well defined boundary conditions for investigating the flow experiments. The walls of the microchannels were functionalized to induce different kinds of surface anchoring of the 5CB molecules: degenerate planar, uniform planar, and homeotropic surface anchoring. Channels possessing composite anchoring conditions (hybrid) were additionally fabricated, e. g. homeotropic and uniform planar anchoring within the same channel. On filling the microchannels with 5CB in the isotropic phase, different equilibrium configurations of the nematic director resulted, as the sample cooled down to nematic phase. For a given surface anchoring, the equilibrium director configuration varied also with the channel aspect ratio. The static director field within the channel registered the initial conditions for the flow experiments. The static and i ii dynamic experiments have been analyzed using a combination of polarization, and confocal fluorescence microscopy techniques, along with particle tracking method for measuring the flow speeds. Additionally, dual-focus fluorescence correlation spectroscopy is introduced as a generic velocimetry tool for liquid crystal flows.The flow of nematic liquid crystals is inherently complex due to the coupling between the flow and the nematic director. The presence of the four confining walls and the nature of surface anchoring on them complicate the flow-director interactions further. In microchannels possessing degenerate planar anchoring, four different flow-induced defect textures were identified with increasing Ericksen number: π-walls, disclination lines pinned to the channel walls, disclination lines with one pinned and one freely suspended end, and disclination loops freely flowing in a chaotic manner. However, such textures and sequence of defects were not observed for flows within channels with homogeneous anchoring.Using experiments and numerical modeling...

show abstract

Flows of Anisotropic Liquids

2009

View full text Add to dashboard Cite

j45 crystals, presented in Chapter 2. The connection between translation motions and the orientational ones described accordingly in terms of a velocity field v(r, t) and a director field n(r, t) can be considered as a fundamental physical property of liquid crystals. It is responsible for a number of specific phenomena existing in liquid crystal media. Some of them, such as various instabilities induced by electric fields in thin layers of nematic liquid crystals or backflow effects arising at the turning off electric fields are of great practical importance (Chapter 6).The connection between v(r, t) and n(r, t) also results in a number of linear and nonlinear phenomena in flows of liquid crystals. In general, liquid crystals show non-Newtonian rheological behavior. It means, for example, that apparent shear viscosity depends on the shear rate. At the same time, strong magnetic (electric) fields allow to stabilize orientational structure. In thin layers of LC, the proper surface treatment can also provide the given orientation (e.g., planar or homeotropic, see Chapter 2). Liquid crystal with a stabilized orientational structure can be considered a conventional Newtonian fluid with shear viscosity determined by a field direction [1] or by a surfaceinduced direction. Such rheological behavior has to be taken into account at viscometric studies of liquid crystals. It will be described in detail in Chapter 5.A number of interesting flow-induced phenomena in smectic A and C phases are out of scope of this book. A reader can find description of such effects in Oswald and Pieranski [2] and in original papers [3,4]. We also do not consider rheological behavior of polymeric liquid crystals, lyotropic liquid crystals, and active liquid crystals. The last two classes of LC materials are of interest for understanding very complicated phenomena existing in living nature. In particular, active liquid crystals show unusual rheological properties that demand a special consideration [5][6][7].

show abstract

Simulations of liquid crystals in Poiseuille flow

Cited by 32 publications

References 23 publications

The effect of anchoring on the nematic flow in channels

The effect of anchoring on the nematic flow in channels

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Flows of Anisotropic Liquids

Contact Info

Product

Resources

About