Microscope textures of nematic droplets in polymer dispersed liquid crystals

Ondris-Crawford, R. J.; Boyko, E. P.; Wagner, Brian G.; Erdmann, John H.; Žumer, S.; Doane, J. William

doi:10.1063/1.348840

Cited by 247 publications

(136 citation statements)

References 15 publications

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“…This issue becomes even more complicated if to consider liquid crystal (LC) droplets [2][3][4][5][6][7], for example, polymer-dispersed liquid crystal (PDLC) films because orientation structure within the droplets is commonly inhomogeneous. Configuration of LC director (a unit vector n characterizing preferred molecular orientation for a local volume in a droplet) can be rather complicated [2,3,7]. Consecutive development of special simulation techniques by many research groups (see, for instance, the lists of some of them in [6,7]) allows now calculating adequately the light scattering pictures for actual LC dispersions.…”

Section: Introductionmentioning

confidence: 99%

Experimental results and theoretical model to describe angular dependence of light scattering by monolayer of nematic droplets

Loiko¹,

Krakhalev²,

Konkolovich³

et al. 2016

Journal of Quantitative Spectroscopy and Radiative Transfer

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Light scattering by a monolayer of bipolar nematic droplets encapsulated in polymer film is examined both experimentally and theoretically. A method for the simulation of the angular distribution of scattered light is based on the anomalous diffraction and interference approximations taking into account the director configuration within liquid crystal droplets and their bipolar axes orientation. The director configuration in nematic droplets is calculated using the relaxation method of the free energy minimization. The characteristics of the sample, including distribution of droplet sizes and shape anisometry, are measured in details. The experimental results and theoretical data agree closely with each other.

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Section: Introductionmentioning

confidence: 99%

Experimental results and theoretical model to describe angular dependence of light scattering by monolayer of nematic droplets

Loiko¹,

Krakhalev²,

Konkolovich³

et al. 2016

Journal of Quantitative Spectroscopy and Radiative Transfer

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“…The fluorescence confocal signal intensity I was calculated from the local director n and laser polarization P as I ∝ ( n · P) 4 and POM micrographs were calculated with the Jones 2 × 2 matrix formalism [194]. different equilibrium director configurations were observed numerically: symmetric, asymmetric, escaped, and horizontal.…”

Section: Microchannels With Homeotropic Surface Anchoringmentioning

confidence: 99%

“…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

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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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“…The starting configurations of the lattice were chosen to be completely aligned along the z direction and the evolution of the system was followed according to the classic Metropolis Monte Carlo procedure [18]. Polarizing microscope textures were simulated by means of a Müller matrix approach [19], assuming the molecular domains represented by the spins to act as retarders on the light propagating through the sample [20]. As mentioned before we have investigated uniaxial and biaxial droplets with different anchoring at the surfaces and now we report results for the various cases studied.…”

Section: The Model Dropletsmentioning

confidence: 99%