Mechanism of Surface Alignment in Nematic Liquid Crystals

Creagh, Linda T.; Kmetz, A. R.

doi:10.1080/15421407308083389

Cited by 207 publications

(67 citation statements)

References 9 publications

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“…In some sense this conclusion ap− pears to be complementary of the empirical Creagh's concep− tion [1,2]. Our observations show that the gradual change of the surface energy of rigid surface can describe not only the limiting cases of LC orientation (q LC = 0, 90°) but also control the tilt of LC between planar and homeotropic alignment.…”

Section: Resultssupporting

confidence: 74%

“…Orientation of liquid crystals (LCs) on various surfaces has been actively investigating in the last decades [1][2][3][4][5] due to necessity of perfectly aligned panels in LCD industry and because of serious fundamental aspects of LC various an− choring phenomena. One of advanced orientation techni− ques implies photosensitive polymer layers irradiated with polarised UV−light [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

“…We suggested that the cause of this effect is the temperature−dependent competition between aligning abili− ties of the main chain fragments and flexible photosensitive fragments which concentration depends on UV−exposure. According to empirical Creagh's conception [1,2] the homeotropic alignment of LC is realised at g S < g LC while the planar alignment occurs at g LC < g S (g S is the surface ten− sion of the substrate and g LC is the surface tension of LC). Therefore, one can expect a peculiarity of the contact angle in the vicinity of the light−induced anchoring transition.…”

Section: Introductionmentioning

confidence: 99%

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Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

Gvozdovskyy¹,

Kurioz²,

Reznikov³

2009

Opto-Electronics Review

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We report on first studies of wetting of liquid crystal on photoaligning surface. We observed strong light-induced variations of a contact angle of a liquid LC 5CB on a photoaligning surface of fluoro-polyvinyl-cinnamate (PVCN-F) and we connected these variations with changes of PVCN-F polarity. We also present drastic changes of the contact angle of a nematic liquid crystal (MLC-6080) on the PVCN-F surface in a vicinity of temperature anchoring transition of liquid crystal from homeotropic orientation to planar one. We did not find any peculiarities in temperature dependence of the contact angle of isotropic liquid (glycerol) on PVCN-F and of nematic liquid crystal on pure glass in the same temperature range. It allows us to suggest that rearrangement of LC molecules and flexible fragments in the LC-polymer interface are responsible for the change of surface tensions both of LC and polymer and the observed jump of the contact angle.

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Section: Resultssupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

Gvozdovskyy¹,

Kurioz²,

Reznikov³

2009

Opto-Electronics Review

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“…In the cell with rubbed PI ALs, small domains of BP merge along the rubbing direction first. As the temperatures are lowered, further domains merge in the lateral direction also, forming textures of higher uniformity, see Figure 3(b) for textures at 46.0 C, 45.4 C, and 44.6 C. The topological defects on the poly-imide (PI) layer created by the rubbing process 9 are most likely the cause of this behavior. As the process of oblique evaporation of SiO 2 does not create such topological defects, these lines were absent in type-2 cells (Figure 1(b)), confirming our suspicion.…”

mentioning

confidence: 99%

On the effect of alignment layers on blue phase liquid crystals

Joshi

Shang

Smet

et al. 2015

Applied Physics Letters

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In the present work, the effect of alignment layers on blue phase liquid crystals was investigated. It was found that homogeneous alignment layers have profound selective influence on blue phase II (BPII). In the absence of alignment layers, BPII domains were randomly oriented and showed weak Bragg reflection in the UV, whereas with assistance of anchoring uniform domains with sharp Bragg reflection in the visible range appeared. On the other hand, the magnitude of Bragg shift in response to alignment layers in BPI is negligible. Domains of BP with alignment layers exhibit sharp Bragg reflection peaks (with FWHM < 15 nm), with very vivid colors and possessing fast switching speeds (<5 ×10−4 s). This simple method of selectively assisting one of the cubic phases is expected to be advantageous in the comparative studies of the two phases.

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“…48 Homeotropic alignment can also be achieved using a hydrophobic film. 49 The LC reorientation in the middle of the LC cell can be controlled by the strong interaction (also called 'anchoring') between LC molecules and the substrate surface.…”

Section: Twisted Nematic (Tn) Configurationmentioning

confidence: 99%

Fundamentals of phase-only liquid crystal on silicon (LCOS) devices

2014

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This paper describes the fundamentals of phase-only liquid crystal on silicon (LCOS) technology, which have not been previously discussed in detail. This technology is widely utilized in high efficiency applications for real-time holography and diffractive optics. The paper begins with a brief introduction on the developmental trajectory of phase-only LCOS technology, followed by the correct selection of liquid crystal (LC) materials and corresponding electro-optic effects in such devices. Attention is focused on the essential requirements of the physical aspects of the LC layer as well as the indispensable parameters for the response time of the device. Furthermore, the basic functionalities embedded in the complementary metal oxide semiconductor (CMOS) silicon backplane for phase-only LCOS devices are illustrated, including two typical addressing schemes. Finally, the application of phase-only LCOS devices in real-time holography will be introduced in association with the use of cutting-edge computer-generated holograms. The architecture of LCOS devices is similar to conventional LC devices except that a silicon backplane constitutes one of the substrates (Figure 1). The silicon CMOS backplane consists of the electronic circuitry that is buried underneath pixel arrays to provide a high 'fill factor'. The pixels are aluminum mirrors deposited on the surface of the silicon backplane. The incident light is transmitted through the LC layer with almost zero absorption. The integration of high-performance driving circuitry allows the applied voltage to be changed on each pixel, thereby controlling the phase retardation of the incident wavefront across the device. Currently, there are two types of light modulation using LCOS devices, amplitude modulation and phase modulation. In the former case, the amplitude of the light signal is modulated 6,7 by varying the linear polarzation direction of the incident light passing through a linear polarizer, the same principle used in a standard LC television. In the latter case, the phase delay is accomplished by electrically adjusting the optical refractive index along the light path, which is possible because of the non-zero birefringence of the LC materials in use but should be carefully characterized. [8][9][10][11][12][13] In a phase-only LCOS SLM modulator, no light absorption by polarizers or other light-absorbing components will occur, such that the maximum light efficiency can be expected.Currently, most of the conventional LC devices are not able to efficiently modulate the phase of an incident wavefront. For instance, the LC device structure using thin film transistors is not suitable for phase modulation because an appropriate electro-optic effect has not been used (see the section on 'Twisted nematic (TN) configuration' and the section on 'VAN configuration' for details). Moreover, the pixels of this type of device are too large to provide acceptably large diffraction angles. In addition, the pixel circuitry and connection tracks are in the light path such that the ...

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Mechanism of Surface Alignment in Nematic Liquid Crystals

Cited by 207 publications

References 9 publications

Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

On the effect of alignment layers on blue phase liquid crystals

Fundamentals of phase-only liquid crystal on silicon (LCOS) devices

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