Reversible change in alignment mode of nematic liquid crystals regulated photochemically by command surfaces modified with an azobenzene monolayer

Ichimura, Kunihiro; Suzuki, Yoshishige; Seki, Takahiro; Hosoki, Akira; Aoki, Koso

doi:10.1021/la00083a030

Cited by 694 publications

(385 citation statements)

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“…In most of the previous experiments, the solid interface was fixed. Here we use a so-called command surface (13) for LC alignment and its real-time control; the director manipulation is achieved by manipulating the anchoring condition through a lightinduced isomerization of a photoactive azo-dendrimer adsorbed at the surface of microrods. As the light-induced isomerization takes place, the anchoring conditions provided by the cis isomer are different from those of the trans isomer.…”

mentioning

confidence: 99%

Optically driven translational and rotational motions of microrod particles in a nematic liquid crystal

Eremin

Hirankittiwong

Chattham

et al. 2015

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

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A small amount of azo-dendrimer molecules dissolved in a liquid crystal enables translational and rotational motions of microrods in a liquid crystal matrix under unpolarized UV light irradiation. This motion is initiated by a light-induced trans-to-cis conformational change of the dendrimer adsorbed at the rod surface and the associated director reorientation. The bending direction of the cis conformers is not random but is selectively chosen due to the curved local director field in the vicinity of the dendrimer-coated surface. Different types of director distortions occur around the rods, depending on their orientations with respect to the nematic director field. This leads to different types of motions driven by the torques exerted on the particles by the director reorientations.L iquid crystals (LCs) are self-organized mesomorphic materials that exhibit various symmetries and structures (1). They are widely used in flat panel displays for their exceptional electrooptical properties and a combination of orientational elasticity and fluidity. For example, nematic LCs (NLCs) are distinguished by their long-range orientational order, which favors alignment of the molecules (mesogens) in a preferred direction denoted as the director n. An exceptional feature of NLCs is that, despite their fluidity, they exhibit anisotropic optical and mechanical properties, and thus can transmit mechanical torque because of directional elasticity (1). Such torque occurs in response to deformations away from a uniform equilibrium state.Such unique features of LCs can be exploited for designing smart multifunctional materials. Among these materials, colloidal dispersions of microparticles and nanoparticles in LCs have been actively studied in research on soft-matter physics (2-7). Tunable anisotropic interactions between microparticles dispersed in LCs give rise to self-assembled 1D and 2D colloidal structures (6,8,9). Such colloidal dispersions are interesting not only from a fundamental point of view but also from a technological one. A wide range of self-assembled structures of particles and topological defects stabilized by LC-mediated interactions find numerous applications in designing metamaterials (10), photonic devices (5, 11), sensors (12), and microrheology (5,(10)(11)(12). Here, we demonstrate a phenomenon that can be used in intelligent devices using colloidal dispersions: controlled light-driven translational and rotational motions of microrods in a NLC matrix.The orientation of LC molecules at an interface is governed by anchoring conditions, i.e., whether the director is perpendicular (homeotropic) or parallel (planar) to the interface. The orientation of the director at surfaces can be controlled through interfacial energy, anisotropy of the surface tension, and surface topography, by the pretreatment of the surfaces using surface agents, such as polymers and surfactants, together with mechanical or optical treatments. In most of the previous experiments, the solid interface was fixed. Here we use a so-called comm...

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mentioning

confidence: 99%

Optically driven translational and rotational motions of microrod particles in a nematic liquid crystal

Eremin

Hirankittiwong

Chattham

et al. 2015

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

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“…The similar behaviour of absorption spectra was observed for 1b′ maintaining tert-Boc groups in CH 3 CN solution which is the typical phenomenon shown between the E and Z isomerization states of azobenzene derivatives. 46, 47 The thermal stability of Z isomer of 75 1b′ in CH 3 CN at 22 °C, (the temperature at which microtubule motility assay has been done) was also confirmed under the dark condition (inset). Only very small percentage of Z isomer of 1b′ converts into E isomer after 1h and for a complete recovery, it takes more than 24 h (Fig.…”

Section: Resultsmentioning

confidence: 84%

Dynamic photo-control of kinesin on a photoisomerizable monolayer – hydrolysis rate of ATP and motility of microtubules depending on the terminal group

2012

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The reversibly and repeatedly altered gliding motility of microtubules driven by kinesin on the photoresponsive monolayer surface is studied. It was confirmed that an azobenzene monolayer surface needs to have free amino terminal groups for the successful dynamic control of the motility of microtubule. The surface of azobenzene monolayer with terminal amino groups can dynamically control 10 the ATP hydrolysis activity of kinesin which resulted in the change in motility of microtubule.

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“…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.…”

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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Reversible change in alignment mode of nematic liquid crystals regulated photochemically by command surfaces modified with an azobenzene monolayer

Cited by 694 publications

References 0 publications

Optically driven translational and rotational motions of microrod particles in a nematic liquid crystal

Optically driven translational and rotational motions of microrod particles in a nematic liquid crystal

Dynamic photo-control of kinesin on a photoisomerizable monolayer – hydrolysis rate of ATP and motility of microtubules depending on the terminal group

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

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