Physics of colloidal dispersions in nematic liquid crystals

Stark, Holger

doi:10.1016/s0370-1573(00)00144-7

Cited by 628 publications

(695 citation statements)

References 182 publications

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“…S1A). The resulting configuration of the director field around the particle has a dipolar symmetry and leads to anisotropic interactions [16][17][18][19][20][21] reminiscent of the interaction between electric dipoles. The pair interaction is of the order of several thousand k B T , leading to the formation of stable colloidal structures such as chains or two-and three-dimensional crystals.…”

Section: Introductionmentioning

confidence: 99%

Colloidal caterpillars for cargo transportation

et al. 2014

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Tunable transport of tiny objects in fluid systems is demanding in diverse fields of science such as drug delivery, active matter far from equilibrium, and lab-on-a-chip applications. Here, we report the directed motion of colloidal particles and self-assembled colloidal chains in a nematic liquid crystal matrix using electrohydrodynamic convection (EHC) rolls. The asymmetric distortion of the molecular orientation around the particles results -for single particles -in a hopping motion from one EHC roll to the next and -for colloidal chains -in a caterpillar-like motion in the direction perpendicular to the roll axes. We demonstrate the use of the colloidal chains as micro traction engines for the transport of various types of micro cargo.

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Section: Introductionmentioning

confidence: 99%

Colloidal caterpillars for cargo transportation

et al. 2014

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“…A period of lull followed till the novel colloidal interactions in liquid crystals were discovered by the seminal work of Poulin et al in the late 1990s [24]. Several numerical investigations were undertaken thereafter, especially on flow past inclusions [25] and the effects of flow on topological defects [26] around the inclusions [27][28][29].…”

Section: Motivationmentioning

confidence: 99%

“…Defined as: 25) the extrapolation length gives an estimation of the nematic elasticity in comparison to the surface anchoring. In the limit of strong anchoring, the extrapolation length is of the order of few nanometers.…”

Section: Surface Anchoringmentioning

confidence: 99%

“…Different boundary conditions at the colloid-nematic interface lead to different orientations of the director at the surface [122]. This results in a wide variety of phenomena [25], which has consequently lead to novel routes to self-assembled structures [123][124][125][126][127][128]. Interestingly, nematic colloids or rather emulsions of water droplets, were first employed for revealing the nematic director field [129].…”

Section: Nematic Colloidsmentioning

confidence: 99%

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Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Sengupta

Herminghaus

Bahr

2011

Molecular Crystals and Liquid Crystals

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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...

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“…In recent years there has been much interest in the physics and possible technological applications of colloidal suspensions in a liquid crystal host [1]. As early as 1970, Brochard and de Gennes [2] pointed out that if the colloidal particles possess a permanent magnetic moment, then the orientation of the local moments and the nematic director would be coupled, and this would give rise to some new and interesting physical effects.…”

Section: Introductionmentioning

confidence: 99%

Fredericksz Transition Threshold in Nematic Liquid Crystals Filled with Ferroelectric Nano-Particles

Reshetnyak

Shelestiuk

Sluckin

2006

Molecular Crystals and Liquid Crystals

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A key liquid crystalline property for electro-optic applications is the Frederiks threshold electric field. There has been recent experimental interest in liquid crystal-based colloidal suspensions in which the colloidal nanoparticles both possess a permanent electric polarization and provide strong director anchoring on the particle surface. Such suspensions are sometimes known as Filled Liquid Crystals. Our calculations suggest, in qualitative agreement with experiment, that filling the nematic liquid crystal with ferroelectric nanoparticles can significantly decrease the electric Frederiks transition threshold field.

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Physics of colloidal dispersions in nematic liquid crystals

Cited by 628 publications

References 182 publications

Colloidal caterpillars for cargo transportation

Colloidal caterpillars for cargo transportation

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Fredericksz Transition Threshold in Nematic Liquid Crystals Filled with Ferroelectric Nano-Particles

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