The alignment of nematic liquid crystals on photolithographic micro-groove patterns

Kawata, Yasushi; Takatoh, Kohki; Hasegawa, M.; Sakamoto, Masanori

doi:10.1080/02678299408027872

Cited by 49 publications

(20 citation statements)

References 15 publications

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“…Understanding and controlling defects in LCs are important to many technological applications (e.g., displays and optical switches). Because the defects are considered to be anomalies in the LC structure, general efforts have been directed at minimizing or annealing the defects, including by using microstructures (grooves and gratings) (6)(7)(8). However, defect domains possess unique rheological and optical properties, which could potentially be exploited to make novel materials.…”

mentioning

confidence: 99%

Ordered patterns of liquid crystal toroidal defects by microchannel confinement

Choi

Pfohl

Zhang

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

105

113

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In this article we present experimental results demonstrating an approach to controlling the size and spatial patterning of defect domains in a smectic liquid crystal (LC) by geometric confinement in surface-modified microchannels. By confining the LC 4-octyl-4-cyanobiphenyl in m-sized rectangular channels with controlled surface polarity, we were able to generate defect domains that are not only nearly uniform in size but also arranged in quasi-2D ordered patterns. Atomic force microscopy measurements revealed that the defects have a toroidal topology, which we argue is dictated by the boundary conditions imposed by the walls of the microchannel. We show that the defects can be considered to be colloidal objects, which interact with each other to form ordered patterns. This method opens the possibility for exploiting the unique optical and rheological properties associated with LC defects to making new materials. For example, the control of the shape, size, and spatial arrangement of the defects at the mesoscale suggests applications in patterning, templating, and when extended to lyotropic LCs, a process leading to uniform-sized spherical particles for chemical encapsulation and delivery. S mectic (Sm) liquid crystals (LCs) are composed of elongated molecules that are aligned and arranged in layers. Local disruptions in the orientational, positional (layering), or morphological (bending) order in a Sm LC result in defects, which, when observed under crossed polarizers, exhibit complex textural patterns. The texture, which results from the highly anisotropic polarization of the molecules, has been extensively characterized and categorized based on the type of the LC structure (1-5). Understanding and controlling defects in LCs are important to many technological applications (e.g., displays and optical switches). Because the defects are considered to be anomalies in the LC structure, general efforts have been directed at minimizing or annealing the defects, including by using microstructures (grooves and gratings) (6-8). However, defect domains possess unique rheological and optical properties, which could potentially be exploited to make novel materials. The prerequisite for doing so would be the control of the type, size, and spatial distribution of the defects, which had not been well addressed in previous studies.In this article we present experimental results demonstrating the control of the size and spatial distribution of toroidal defects in the Sm LC 4Ј-octyl-4-cyanobiphenyl (8CB) by using surfacemodified microchannels. By changing the depth and width of the m-scale channels with a controlled surface polarity, we were able to generate focal conic defects that are not only nearly uniform in size but also arranged in 2D ordered patterns. This process is analogous to colloidal crystallization, except here the ''colloids'' are the ''soft'' m-sized defects within the LC. In addition, whereas the ordering in colloids is caused by interparticle interactions, here the defect ordering results from the competitio...

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mentioning

confidence: 99%

Ordered patterns of liquid crystal toroidal defects by microchannel confinement

Choi

Pfohl

Zhang

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

105

113

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“…Although the absolute values of the ratios are about one order of value higher than accordii to equation ( 6), the general trend follows theory.…”

Section: Resultsmentioning

confidence: 80%

“…where u and q are the amplitude and the wave-vector of the periodic distortion of the surface. K is effective elastic constant of the liquid crystal (formula ( 6 ) is derived in a single-constant approximation). If to neglect difference betweem K and K2 one can relate (using ( 6)) experimentally determined ratios A/& to the parameters of the grating.…”

Section: Resultsmentioning

confidence: 99%

Studies of the Anchoring Energy of Nematics on Grooved Surfaces

Konovalov

Muravski

Pelzl

2001

Molecular Crystals and Liquid Crystals Science and Technology.

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Previously we developed optical method enabling measurements of the liquid crystal twist angle in the cells with grooved surfaces. In this work azimuthal anchoring energy of a liquid crystal to a surface i s estimated by measuring the deviation of the twist angle of the liquid crystal from the angle defined by direction of liquid crystal alignment on one rubbed and one grooved surfaces substrates. It was found that the twist angle in the cells depends not only on the parameters of the grooves, but also strongly depends on the material covering the grooves.

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“…On the other hand, it is known that liquid crystals are aligned by surfaces having microgrooves. 3,4 Moreover, a combination of LCs with gratings is interesting from both applicatory and fundamental points of view. This combination results in various electro-optic devices such as controllable diffraction elements (gratings, Fresnel lenses).…”

Section: Introductionmentioning

confidence: 99%

Properties and mechanism of multi‐domain vertically aligned mode on a grid surface

et al. 2003

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Abstract— Electro‐optical properties of grid‐aligned multi‐domain (GAMD) textures in homeotropically aligned nematic liquid‐crystal displays have been studied as a function of grid parameters. It is experimentally verified that with higher height and smaller pitch of the grid, a more‐stable multidomain structure can be obtained. To predict the grid properties and the mechanism of their action, both computations and experimental results are presented. The weak‐anchoring conditions are assumed in the computations on the base of the measured anchoring‐strength data to obtain more reliable parameters. A test liquid‐crystal cell has been prepared after adjusting the grid parameters, and it has shown very high gray‐level stability, a nice viewing angle, and fast response.

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The alignment of nematic liquid crystals on photolithographic micro-groove patterns

Cited by 49 publications

References 15 publications

Ordered patterns of liquid crystal toroidal defects by microchannel confinement

Ordered patterns of liquid crystal toroidal defects by microchannel confinement

Studies of the Anchoring Energy of Nematics on Grooved Surfaces

Properties and mechanism of multi‐domain vertically aligned mode on a grid surface

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