Photoalignment of liquid crystals: basics and current trends

Yaroshchuk, O.; Reznikov, Yuriy

doi:10.1039/c1jm13485j

Cited by 469 publications

(346 citation statements)

References 174 publications

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“…The molecules generally align on the azimuthal plane in a direction perpendicular to the UV polarization. Alternative photosensitive polymers can effect the LC alignment even parallel to the UV polarization [165]. The contact angle values of PVCN-F coated surfaces are slightly higher than those with PVA coating on respective surfaces (Table 4.1).…”

Section: Anchoring Characterization Of Functionalized Substratesmentioning

confidence: 96%

“…On the one hand, this method complements existing techniques of guided transport; on the other hand, it offers several competitive advantages, including the possibility of in situ switching between targets and minimal design challenges. In addition to the in situ switching demonstrated here, there are also established techniques at hand to switch between different states of anchoring at the walls and thereby to navigate the disclination lines by external control [165,180]. This approach is well suited for guiding a wide range of softmatter entities including colloidal particles and droplets of aqueous solutions, heralding the first steps towards Topological Microfluidics.…”

Section: Navigating the Topological Defect At A Flow Bifurcationmentioning

confidence: 99%

“…Once the disclination approaches the lower arm, it fuses with the hitherto pinned defect line and stabilizes there. In addition to the dis- cussed switching technique, one can design surfaces in a way that different anchoring states are stabilized, e. g., by appropriate coating with grafted azo-benzene compounds showing photo-induced isomerization [165], or by means of micropatterned surfaces [180]. In Chapter 7.1, we shall employ the disclination for transporting colloidal cargo -particles, droplets etc.…”

Section: Navigating the Topological Defect At A Flow Bifurcationmentioning

confidence: 99%

“…2.5), are generated on substrates by employing a variety of chemical and physical methods [63,66,164,165]. In spite of their wide acceptance in both application and research of LCs, attempts to transfer the technology in microfluidic systems have never been reported.…”

Section: Non-trivial Aspects Of Microchannel Functionalizationmentioning

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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Section: Anchoring Characterization Of Functionalized Substratesmentioning

confidence: 96%

Section: Navigating the Topological Defect At A Flow Bifurcationmentioning

confidence: 99%

Section: Navigating the Topological Defect At A Flow Bifurcationmentioning

confidence: 99%

Section: Non-trivial Aspects Of Microchannel Functionalizationmentioning

confidence: 99%

See 2 more Smart Citations

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Sengupta

Herminghaus

Bahr

2011

Molecular Crystals and Liquid Crystals

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“…These alternative methods include the photoalignment technique, nanoimprint lithography, oblique vapor deposition, and IB (ion-beam) irradiation [3,[8][9][10][11][12][13][14][15][16][17][18]. While good experimental results have been obtained from these alternative techniques, more reliable and effective studies of LC alignment are still sought for improving the performance of LCs in LCD applications.…”

Section: Introductionmentioning

confidence: 99%

Solution-Derived Hafnium Lanthanum Oxide Films Prepared Using Ion-Beam Irradiation and Their Applications as Alignment Layers for Twisted-Nematic Liquid Crystal Displays

Oh¹

2016

Transactions on Electrical and Electronic Materials

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We present the alignment characteristics of LC (liquid crystal) molecules on solution-derived HLO (hafnium lanthanum oxide) films fabricated using IB (ion-beam) irradiation. We then demonstrated that LC molecules can be homogeneously and uniformly aligned on the HLO film irradiated at an IB incident energy of 1.2 keV. Physicochemical analysis methods such as atomic force microscopy and X-ray photoelectron spectroscopy were used to verify the LC alignment mechanism on the IB-irradiated HLO film. In addition, the electro-optical performance of a TN (twisted-nematic) cell fabricated using the IB-irradiated HLO film exhibited characteristics superior to those of the conventional TN cell fabricated using a rubbed polyimide layer.

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Stimuli‐Directed Alignment Control of Semiconducting Discotic Liquid Crystalline Nanostructures

Bisoyi¹,

Li²

2013

Intelligent Stimuli‐Responsive Materials

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Photoalignment of liquid crystals: basics and current trends

Cited by 469 publications

References 174 publications

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Solution-Derived Hafnium Lanthanum Oxide Films Prepared Using Ion-Beam Irradiation and Their Applications as Alignment Layers for Twisted-Nematic Liquid Crystal Displays

Stimuli‐Directed Alignment Control of Semiconducting Discotic Liquid Crystalline Nanostructures

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