Phase ordering in nematic liquid crystals

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

doi:10.1103/physreve.64.021701

Cited by 53 publications

(67 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This t 1/2 behavior is in agreement with experimental observations 8,9 and with recent numerical investigations that include back-flow effects. 15 In the absence of adsorbed particles, the surfaces induce a long-range orientational order throughout the entire cell. For a small number of particles adsorbed at the solid surfaces, a similar behavior is observed but the relaxation towards a long-range uniform orientation order is delayed.…”

Section: Discussionmentioning

confidence: 99%

“…15,24 It contains only two phenomenological coefficients (A and U) that depend on the liquid crystal of interest; A controls the energy scale of the model, while U controls the value of the scalar order parameter in the bulk, 18 S bulk ͑ U ͒ϭ 1 4 ϩ 3 4 ͱ1Ϫ 8…”

Section: ͑1͒mentioning

confidence: 99%

“…Coarsening dynamics in nematic LCs have been the subject of numerous experimental observations 8,9 and numerical simulations; [10][11][12][13][14][15] considerable controversy has emerged as to whether the ordering violates dynamical scaling and whether at late stages the system enters a regime characterized by a single length scale L(t). As pointed out in previous studies based on cell-dynamics simulations, 10,11 numerical determination of growth exponents may be affected by transient effects or by the freezing of the system into a metastable configuration caused by numerical pinning of topological defects.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Slow dynamics of thin nematic films in the presence of adsorbed nanoparticles

Grollau

Guzmán

Abbott

et al. 2004

The Journal of Chemical Physics

View full text Add to dashboard Cite

Recent experiments indicate that liquid crystals can be used to optically report the presence of biomolecules adsorbed at solid surfaces. In this work, numerical simulations are used to investigate the effects of biological molecules, modeled as spherical particles, on the structure and dynamics of nematic ordering. In the absence of adsorbed particles, a nematic in contact with a substrate adopts a uniform orientational order, imposed by the boundary conditions at this surface. It is found that the relaxation to this uniform state is slowed down by the presence of a small number of adsorbed particles. However, beyond a critical concentration of adsorbed particles, the liquid crystal ceases to exhibit uniform orientational order at long times. At this concentration, the domain growth is characterized by a first regime where the average nematic domain size L D obeys the scaling law L D (t)ϳt 1/2 ; at long times, a slow dynamics regime is attained for which L D tends to a finite value corresponding to a metastable state with a disordered texture. The results of simulations are consistent with experimental observations.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: ͑1͒mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Slow dynamics of thin nematic films in the presence of adsorbed nanoparticles

Grollau

Guzmán

Abbott

et al. 2004

The Journal of Chemical Physics

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

Theory and Simulation Studies of Self‐Assembly of Helical Particles

Cinacchi

Ferrarini

Frezza

et al. 2016

Self‐Assembling Systems

View full text Add to dashboard Cite

While it is possible to control the enantioselective process by using depletion interactions and faceting of the bulding blocks [5], helices are among the natural objects to focus on when dealing with chirality. New functional materials [9] [10] can be produced by exploiting the intrinsic chirality of the helical structures, which are useful in catalysis and demixing of enantiomers [11] [12]. The importance of the helix in nature is unquestionable: proteins, polysaccharides, DNA and RNA, the so called molecules of life, have a helical structure. The helical shape is exhibited in nature also by microorganisms, like filamentous viruses, and cell organelles, like bacterial flagella. Filamentous viruses are formed by a DNA of RNA core, wrapped by a coating of helically arranged proteins. Well-known examples are Tobacco Mosaic Virus (TMV), the first discovered virus [13], and viruses related to filamentous phage fd, whose mutants are present in nature (M13, fd), while others can be obtained by genetic engineering. They have been widely investigated as models of highly anisotropic, colloidal systems, with the advantage of being essentially monodisperse and that their length, of the order of a micrometer, makes them suitable for imaging techniques, such as optical microscopy. Bacterial flagella are helical macromolecular structures assembled from a single protein (flagellin). Their helical shape can be tuned with high precision by regulating external parameters such as temperature or pH, and their large size, of the order of microns, makes them very handy for optical observations. Because of their shape anisotropy, helical biopolymers and colloidal particles may exhibit liquid crystal phases at high densities [14]. These phases are often tacitly assumed to be the same as those occurring in systems of rod-like particles. However, it cannot be taken for granted that at such high densities the intrinsic helicity of the shape can be neglected. To explore the effect of self-assembly of helical polymers and colloids, and in particular to discover whether there is anything special just determined by the helical shape, we have undertaken a comprehensive investigation of the phase behavior of hard helices [15][16][17][18][19], interacting through purely steric repulsions, using Monte Carlo simulations and an extension of Onsager theory [20], a density functional theory (DFT) that was originally proposed to explain the onset if nematic ordering in a system of hard rods. These studies have revealed an unexpectedly rich phase behavior, the most interesting result being the existence of special phases characterized by screw -like ordering. Such kind of organization had been proposed for DNA, based on theoretical considerations [21], and had been observed in dense suspensions of flagellar filaments [22]. Hard helices are an athermal system: phase transitions are controlled by density and are driven by the entropy gain on moving from the less to the more ordered phase. This is a minimalist model, possibly insufficient to account entir...

show abstract

Phase ordering in nematic liquid crystals

Cited by 53 publications

References 29 publications

Slow dynamics of thin nematic films in the presence of adsorbed nanoparticles

Slow dynamics of thin nematic films in the presence of adsorbed nanoparticles

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Theory and Simulation Studies of Self‐Assembly of Helical Particles

Contact Info

Product

Resources

About