Weak surface anchoring of liquid crystals

Bryan‐Brown, G. P.; Wood, E. L.; Sage, Ian

doi:10.1038/20646

Cited by 123 publications

(86 citation statements)

References 10 publications

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“…A simple model used to simulate the transition not only showed good agreement with the experiment but also revealed that the polar surface energies of the frustrated boundary are only 1=10 of typical values. Weak surface anchoring energies are virtuous for lowering device energy consumption and response time [9]. Figure 1 shows a subset of the microtextured substrates employed in this study.…”

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confidence: 99%

Liquid Crystal Orientation Transition on Microtextured Substrates

et al. 2003

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A uniform alignment of liquid crystal (LC) with finite pretilt was observed on microtextured substrates that were lithographically fabricated with alternating horizontal and vertical corrugations. As the period of alternation was decreased toward 0:8 m, the nematic LC alignment on these substrates changed from inhomogeneous in plane, copying the substrate corrugations, to a uniform configuration with a large pretilt of 40 . This transition is pertinent to a frustrated boundary wherein a lowering in the LC elastic energy due to spatial variation in the LC orientation compromises an increase in the surface anchoring energy. A model based on this idea demonstrates good agreement with the experiment. This result may open up a new arena for tailoring substrate characteristics for LC alignment. DOI: 10.1103/PhysRevLett.91.215501 PACS numbers: 61.30.Hn, 61.30.Dk, 61.30.Eb Substrate conditioning for the alignment of liquid crystal (LC) molecules is essential to the operation of LC displays. Most existing techniques used to produce the alignment effect involve uniform treatment of the substrate surface. An unconventional approach to uniform LC alignment, based on inhomogeneous patterning of the substrate, was proposed some time ago [1,2]. The idea is to create a situation wherein the LC director, in coping with the inhomogeneous substrate pattern, acquires so large an elastic energy that the LC has to compromise with a uniform configuration. In general, this frustrated boundary condition can be achieved by making the pattern period small enough. A few versions of this idea, including the use of inhomogeneous surfactant treatment [1,3] and inhomogeneous rubbing [4], have been reported successful. More recently, an interesting application of these substrates in multistable display, which may potentially lead to lower energy consumption, was demonstrated [5,6]. In these demonstrations, the LC director makes zero pretilt with the substrate, and the switching between different stable LC states was achieved by varying an in-plane electric field. However, out-of-plane switching is preferred since the electric field can be more uniform. But that requires the LC pretilt to be finite [7], which has not been found in any reported embodiments [1,3,4]. In yet some designs, a large LC pretilt is crucial as it widens the range of LC elastic constants usable, which would otherwise be too narrow to be practical [8]. Here we show that on lithographically made substrates with alternating horizontal and vertical corrugations, the nematic alignment undergoes an orientational transition that results in a large pretilt angle (40 ). A simple model used to simulate the transition not only showed good agreement with the experiment but also revealed that the polar surface energies of the frustrated boundary are only 1=10 of typical values. Weak surface anchoring energies are virtuous for lowering device energy consumption and response time [9]. Figure 1 shows a subset of the microtextured substrates employed in this study. They consist of arra...

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Liquid Crystal Orientation Transition on Microtextured Substrates

et al. 2003

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“…In fact, the threshold voltage indirectly depends on the RM doping concentration in terms of the polar anchoring energy, in such way that it decreases with decreasing anchoring energy. Moreover, as shown in Figure 4(a), the slope of the EO curve of the LC cell with a 2.5 wt% RM concentration was quite steep, indicating the weak-anchoring case [24]. Now, the polar anchoring energy is determined using a high-electric-field method [25][26][27][28].…”

Section: Resultsmentioning

confidence: 99%

The domain mixing effect on the electro-optical properties of liquid crystals using polyimide doped with reactive mesogen

Kim

Suh

et al. 2016

Journal of Information Display

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“…The threshold intensity is determined by three balancing factors that interact with an optical field of polarized light: molecular polarizability, bulk elasticity and surface anchoring. Considering previous reports, 16,30,31 it is assumed that the threshold intensity for photoinduced molecular reorientation can be reduced by weakening the surface anchoring. This assumption was confirmed by direct evaluation of optical nonlinearity in self-diffraction ring measurements.…”

Section: Evaluation Of Optical Nonlinearity Of Pslcsmentioning

confidence: 99%

“…[30][31][32][33][34] Seki et al 33 and Aoki et al 34 revealed that the packing density of azobenzene units over the substrate surface influences the molecular reorientation behavior of LCs. Here we report that surface treatment drastically affects and reduces the threshold intensity for molecular reorientation in dye-doped LCs.…”

Section: Introductionmentioning

confidence: 99%

Effect of surface treatment on molecular reorientation of polymer-stabilized liquid crystals doped with oligothiophene

Usui

Katayama

Wang

et al. 2016

Polym J

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Irradiation of dye-doped liquid crystals (LCs) with linearly polarized light leads to molecular reorientation, which manifests functional properties for various nonlinear optical (NLO) applications. Material designs with lower light intensity thresholds for molecular reorientation have been explored, and nematic LCs have been one of the most attractive choices because of the high NLO properties. Here we present a different approach to reduce light intensity for reorientation by modifying a substrate surface that controls initial molecular orientation in polymer-stabilized nematic LCs doped with oligothiophene. The surface of the glass substrate was treated with various concentrations of a silane coupler. Water contact angle measurement and analysis of samples using polarized optical microscopy revealed that surface anchoring in the initial state decreased as the silane coupler concentration decreased. The threshold intensity was successfully reduced by 30% simply by optimizing the silane coupler concentration. This finding clearly indicates that weak surface anchoring is key to the reduction of light intensity for molecular reorientation. INTRODUCTIONLiquid crystal (LC) materials have had a great impact on our modern information society. 1-3 Various LC materials and devices including LC displays, 3 smart windows, 4 reconfigurable optical elements 5 and tunable optical metamaterials 6 have been realized. 2 In these applications, light modulation is the most important factor and is achieved by orientational changes of LC molecules using an external field.Molecular reorientation of conventional LCs has been performed by an electric field. However, molecular reorientation triggered by an optical field has attracted attention because it enables the development of all-optical devices. 7,8 Such photoinduced molecular reorientation includes photochemical and photophysical processes. Photochemical processes control LC orientation through a photochemical reaction, for example, photoisomerization, photocrosslinking or photodegradation. [8][9][10][11][12][13][14] In contrast, a photophysical process exploits the nonlinear optical (NLO) effects of an LC. 7,15 When a homeotropic LC is vertically irradiated with linearly polarized light, the interaction between the optical field and the LC molecules generates a torque to rotate the molecular director along the polarization direction, leading to homogeneous (in-plane) orientation. On the other hand, rotation of the molecular director is disturbed both by the interaction between LCs and the glass substrate surface, a process which is also called surface anchoring, and by bulk elasticity. These torques reach a balance that determines a specific light intensity that allows

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Weak surface anchoring of liquid crystals

Cited by 123 publications

References 10 publications

Liquid Crystal Orientation Transition on Microtextured Substrates

Liquid Crystal Orientation Transition on Microtextured Substrates

The domain mixing effect on the electro-optical properties of liquid crystals using polyimide doped with reactive mesogen

Effect of surface treatment on molecular reorientation of polymer-stabilized liquid crystals doped with oligothiophene

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