The Experts below are selected from a list of 4932 Experts worldwide ranked by ideXlab platform
Ivan I. Smalyukh - One of the best experts on this subject based on the ideXlab platform.
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large area optoelastic manipulation of colloidal particles in liquid crystals using photoresponsive molecular surface monolayers
2011Co-Authors: Angel Martinez, Hector C Mireles, Ivan I. SmalyukhAbstract:Noncontact optical trapping and manipulation of micrometer- and nanometer-sized particles are typically achieved by use of forces and torques exerted by tightly focused high-intensity laser beams. Although they were instrumental for many scientific breakthroughs, these approaches find few technological applications mainly because of the small-area manipulation capabilities, the need for using high laser powers, limited application to Anisotropic Fluids and low-refractive-index particles, as well as complexity of implementation. To overcome these limitations, recent research efforts have been directed toward extending the scope of noncontact optical control through the use of optically-guided electrokinetic forces, vortex laser beams, plasmonics, and optofluidics. Here we demonstrate manipulation of colloidal particles and self-assembled structures in nematic liquid crystals by means of single-molecule-thick, light-controlled surface monolayers. Using polarized light of intensity from 1,000 to 100,000 times smaller than that in conventional optical tweezers, we rotate, translate, localize, and assemble spherical and complex-shaped particles of various sizes and compositions. By controlling boundary conditions through the monolayer, we manipulate the liquid crystal director field and the landscape of ensuing elastic forces exerted on colloids by the host medium. This permits the centimeter-scale, massively parallel manipulation of particles and complex colloidal structures that can be dynamically controlled by changing illumination or assembled into stationary stable configurations dictated by the “memorized” optoelastic potential landscape due to the last illumination pattern. We characterize the strength of optically guided elastic forces and discuss the potential uses of this noncontact manipulation in fabrication of novel optically- and electrically-tunable composites from liquid crystals and colloids.
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optical manipulation of colloids and defect structures in Anisotropic liquid crystal Fluids
2011Co-Authors: Rahul P Trivedi, David Engstrom, Ivan I. SmalyukhAbstract:Optical trapping in Anisotropic Fluids such as liquid crystals shows inherently different behavior compared to that in isotropic media. Anisotropic optical and visco-elastic properties of these materials result in direction-sensitive and polarization-dependent interaction of the focused laser beam with colloidal inclusions, defects and structures of long-range molecular order, providing new means of non-contact optical control. Optical trapping properties are further enriched by laser-induced realignment of the optical axis that can be observed in these liquid crystalline materials at relatively low trapping laser powers. Optical manipulation of particles and defects in these Anisotropic Fluids is of immense importance for their fundamental study and from the standpoint of technological applications such as light-directed colloidal self-assembly and generation of tunable photonic architectures in liquid crystals. We review the basic physical mechanisms related to optical trapping in Anisotropic liquid crystalline Fluids and demonstrate how it can be employed in quantitative studies of colloidal interactions and both topological and mechanical properties of defects.
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self alignment of plasmonic gold nanorods in reconfigurable Anisotropic Fluids for tunable bulk metamaterial applications
2010Co-Authors: Qingkun Liu, Yanxia Cui, Dennis F Gardner, Ivan I. SmalyukhAbstract:We demonstrate the bulk self-alignment of dispersed gold nanorods imposed by the intrinsic cylindrical micelle self-assembly in nematic and hexagonal liquid crystalline phases of Anisotropic Fluids. External magnetic field and shearing allow for alignment and realignment of the liquid crystal matrix with the ensuing long-range orientational order of well-dispersed plasmonic nanorods. This results in a switchable polarization-sensitive plasmon resonance exhibiting stark differences from that of the same nanorods in isotropic Fluids. The device-scale bulk nanoparticle alignment may enable optical metamaterial mass production and control of properties arising from combining the switchable nanoscale structure of Anisotropic Fluids with the surface plasmon resonance properties of the plasmonic nanorods.
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three dimensional structure and multistable optical switching of triple twisted particle like excitations in Anisotropic Fluids
2010Co-Authors: Ivan I. Smalyukh, Yves Lansac, Noel A Clark, Rahul P TrivediAbstract:Chiral nematic liquid-crystal phases consist of rod-shaped molecules that have a preference to twist. However, applied fields force them to exist without the twist. Introducing particle-like twists, so called torons, using laser light relieves this frustration by facilitating the reappearance of the twist. The presence of torons could extend the use of liquid crystals in electro-optic and photonic devices.
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three dimensional structure and multistable optical switching of triple twisted particle like excitations in Anisotropic Fluids
2010Co-Authors: Ivan I. Smalyukh, Yves Lansac, Noel A Clark, Rahul P TrivediAbstract:Control of structures in soft materials with long-range order forms the basis for applications such as displays, liquid-crystal biosensors, tunable lenses, distributed feedback lasers, muscle-like actuators and beam-steering devices. Bistable, tristable and multistable switching of well-defined structures of molecular alignment is of special interest for all of these applications. Here we describe the facile optical creation and multistable switching of localized configurations in the molecular orientation field of a chiral nematic Anisotropic fluid. These localized chiro-elastic particle-like excitations--dubbed 'triple-twist torons'--are generated by vortex laser beams and embed the localized three-dimensional (3D) twist into a uniform background. Confocal polarizing microscopy and computer simulations reveal their equilibrium internal structures, manifesting both skyrmion-like and Hopf fibration features. Robust generation of torons at predetermined locations combined with both optical and electrical reversible switching can lead to new ways of multistable structuring of complex photonic architectures in soft materials.
Aliaksandr V. Kachynski - One of the best experts on this subject based on the ideXlab platform.
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realignment enhanced coherent anti stokes raman scattering and three dimensional imaging in Anisotropic Fluids
2008Co-Authors: Aliaksandr V. Kachynski, Andrey N. Kuzmin, Paras N. Prasad, Ivan I. SmalyukhAbstract:We apply coherent anti-Stokes Raman Scattering (CARS) microscopy to characterize director structures in liquid crystals. We demonstrate that the polarized CARS signal in these Anisotropic Fluids strongly depends on alignment of chemical bonds/molecules with respect to the collinear polarizations of Stokes and pump/probe excitation beams. This dependence allows for the visualization of the bond/molecular orientations via polarized detection of the CARS signal and thus for CARS polarization microscopy of liquid crystal director fields, as we demonstrate using structures in nematic, cholesteric, and smectic liquid crystals. On the other hand, laser-induced director realignment at powers above a well-defined threshold provides the capability for all-optical CARS signal enhancement in liquid crystals. Moreover, since the liquid crystalline alignment can be controlled by electric and magnetic fields, this demonstrates the feasibility of CARS signal modulation by applying external fields to these materials.
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realignment enhanced coherent anti stokes raman scattering cars and three dimensional imaging in Anisotropic Fluids
2008Co-Authors: Aliaksandr V. Kachynski, Andrey N. Kuzmin, Paras N. Prasad, Ivan I. SmalyukhAbstract:We apply coherent anti-Stokes Raman Scattering (CARS) microscopy to characterize director structures in liquid crystals.
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Laser trapping in Anisotropic Fluids and polarization-controlled particle dynamics.
2006Co-Authors: Ivan I. Smalyukh, Aliaksandr V. Kachynski, Andrey N. Kuzmin, Paras N. PrasadAbstract:Anisotropic Fluids are widespread, ranging from liquid crystals used in displays to ordered states of a biological cell interior. Optical trapping is potentially a powerful technique in the fundamental studies and applications of Anisotropic Fluids. We demonstrate that laser beams in these Fluids can generate Anisotropic optical trapping forces, even for particles larger than the trapping beam wavelength. Immersed colloidal particles modify the fluid's ordered molecular structures and locally distort its optic axis. This distortion produces a refractive index “corona” around the particles that depends on their surface characteristics. The laser beam can trap such particles not only at their center but also at the high-index corona. Trapping forces in the beam's lateral plane mimic the corona and are polarization-controlled. This control allows the optical forces to be reversed and cause the particle to follow a prescribed trajectory. Anisotropic particle dynamics in the trap varies with laser power because of the anisotropy of both viscous drag and trapping forces. Using thermotropic liquid crystals and biological materials, we show that these phenomena are quite general for all Anisotropic Fluids and impinge broadly on their quantitative studies using laser tweezers. Potential applications include modeling thermodynamic systems with Anisotropic polarization-controlled potential wells, producing optically tunable photonic crystals, and fabricating light-controlled nano- and micropumps.
Rahul P Trivedi - One of the best experts on this subject based on the ideXlab platform.
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optical manipulation of colloids and defect structures in Anisotropic liquid crystal Fluids
2011Co-Authors: Rahul P Trivedi, David Engstrom, Ivan I. SmalyukhAbstract:Optical trapping in Anisotropic Fluids such as liquid crystals shows inherently different behavior compared to that in isotropic media. Anisotropic optical and visco-elastic properties of these materials result in direction-sensitive and polarization-dependent interaction of the focused laser beam with colloidal inclusions, defects and structures of long-range molecular order, providing new means of non-contact optical control. Optical trapping properties are further enriched by laser-induced realignment of the optical axis that can be observed in these liquid crystalline materials at relatively low trapping laser powers. Optical manipulation of particles and defects in these Anisotropic Fluids is of immense importance for their fundamental study and from the standpoint of technological applications such as light-directed colloidal self-assembly and generation of tunable photonic architectures in liquid crystals. We review the basic physical mechanisms related to optical trapping in Anisotropic liquid crystalline Fluids and demonstrate how it can be employed in quantitative studies of colloidal interactions and both topological and mechanical properties of defects.
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three dimensional structure and multistable optical switching of triple twisted particle like excitations in Anisotropic Fluids
2010Co-Authors: Ivan I. Smalyukh, Yves Lansac, Noel A Clark, Rahul P TrivediAbstract:Chiral nematic liquid-crystal phases consist of rod-shaped molecules that have a preference to twist. However, applied fields force them to exist without the twist. Introducing particle-like twists, so called torons, using laser light relieves this frustration by facilitating the reappearance of the twist. The presence of torons could extend the use of liquid crystals in electro-optic and photonic devices.
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three dimensional structure and multistable optical switching of triple twisted particle like excitations in Anisotropic Fluids
2010Co-Authors: Ivan I. Smalyukh, Yves Lansac, Noel A Clark, Rahul P TrivediAbstract:Control of structures in soft materials with long-range order forms the basis for applications such as displays, liquid-crystal biosensors, tunable lenses, distributed feedback lasers, muscle-like actuators and beam-steering devices. Bistable, tristable and multistable switching of well-defined structures of molecular alignment is of special interest for all of these applications. Here we describe the facile optical creation and multistable switching of localized configurations in the molecular orientation field of a chiral nematic Anisotropic fluid. These localized chiro-elastic particle-like excitations--dubbed 'triple-twist torons'--are generated by vortex laser beams and embed the localized three-dimensional (3D) twist into a uniform background. Confocal polarizing microscopy and computer simulations reveal their equilibrium internal structures, manifesting both skyrmion-like and Hopf fibration features. Robust generation of torons at predetermined locations combined with both optical and electrical reversible switching can lead to new ways of multistable structuring of complex photonic architectures in soft materials.
Paras N. Prasad - One of the best experts on this subject based on the ideXlab platform.
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realignment enhanced coherent anti stokes raman scattering and three dimensional imaging in Anisotropic Fluids
2008Co-Authors: Aliaksandr V. Kachynski, Andrey N. Kuzmin, Paras N. Prasad, Ivan I. SmalyukhAbstract:We apply coherent anti-Stokes Raman Scattering (CARS) microscopy to characterize director structures in liquid crystals. We demonstrate that the polarized CARS signal in these Anisotropic Fluids strongly depends on alignment of chemical bonds/molecules with respect to the collinear polarizations of Stokes and pump/probe excitation beams. This dependence allows for the visualization of the bond/molecular orientations via polarized detection of the CARS signal and thus for CARS polarization microscopy of liquid crystal director fields, as we demonstrate using structures in nematic, cholesteric, and smectic liquid crystals. On the other hand, laser-induced director realignment at powers above a well-defined threshold provides the capability for all-optical CARS signal enhancement in liquid crystals. Moreover, since the liquid crystalline alignment can be controlled by electric and magnetic fields, this demonstrates the feasibility of CARS signal modulation by applying external fields to these materials.
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realignment enhanced coherent anti stokes raman scattering cars and three dimensional imaging in Anisotropic Fluids
2008Co-Authors: Aliaksandr V. Kachynski, Andrey N. Kuzmin, Paras N. Prasad, Ivan I. SmalyukhAbstract:We apply coherent anti-Stokes Raman Scattering (CARS) microscopy to characterize director structures in liquid crystals.
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Laser trapping in Anisotropic Fluids and polarization-controlled particle dynamics.
2006Co-Authors: Ivan I. Smalyukh, Aliaksandr V. Kachynski, Andrey N. Kuzmin, Paras N. PrasadAbstract:Anisotropic Fluids are widespread, ranging from liquid crystals used in displays to ordered states of a biological cell interior. Optical trapping is potentially a powerful technique in the fundamental studies and applications of Anisotropic Fluids. We demonstrate that laser beams in these Fluids can generate Anisotropic optical trapping forces, even for particles larger than the trapping beam wavelength. Immersed colloidal particles modify the fluid's ordered molecular structures and locally distort its optic axis. This distortion produces a refractive index “corona” around the particles that depends on their surface characteristics. The laser beam can trap such particles not only at their center but also at the high-index corona. Trapping forces in the beam's lateral plane mimic the corona and are polarization-controlled. This control allows the optical forces to be reversed and cause the particle to follow a prescribed trajectory. Anisotropic particle dynamics in the trap varies with laser power because of the anisotropy of both viscous drag and trapping forces. Using thermotropic liquid crystals and biological materials, we show that these phenomena are quite general for all Anisotropic Fluids and impinge broadly on their quantitative studies using laser tweezers. Potential applications include modeling thermodynamic systems with Anisotropic polarization-controlled potential wells, producing optically tunable photonic crystals, and fabricating light-controlled nano- and micropumps.
Yves Lansac - One of the best experts on this subject based on the ideXlab platform.
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three dimensional structure and multistable optical switching of triple twisted particle like excitations in Anisotropic Fluids
2010Co-Authors: Ivan I. Smalyukh, Yves Lansac, Noel A Clark, Rahul P TrivediAbstract:Chiral nematic liquid-crystal phases consist of rod-shaped molecules that have a preference to twist. However, applied fields force them to exist without the twist. Introducing particle-like twists, so called torons, using laser light relieves this frustration by facilitating the reappearance of the twist. The presence of torons could extend the use of liquid crystals in electro-optic and photonic devices.
-
three dimensional structure and multistable optical switching of triple twisted particle like excitations in Anisotropic Fluids
2010Co-Authors: Ivan I. Smalyukh, Yves Lansac, Noel A Clark, Rahul P TrivediAbstract:Control of structures in soft materials with long-range order forms the basis for applications such as displays, liquid-crystal biosensors, tunable lenses, distributed feedback lasers, muscle-like actuators and beam-steering devices. Bistable, tristable and multistable switching of well-defined structures of molecular alignment is of special interest for all of these applications. Here we describe the facile optical creation and multistable switching of localized configurations in the molecular orientation field of a chiral nematic Anisotropic fluid. These localized chiro-elastic particle-like excitations--dubbed 'triple-twist torons'--are generated by vortex laser beams and embed the localized three-dimensional (3D) twist into a uniform background. Confocal polarizing microscopy and computer simulations reveal their equilibrium internal structures, manifesting both skyrmion-like and Hopf fibration features. Robust generation of torons at predetermined locations combined with both optical and electrical reversible switching can lead to new ways of multistable structuring of complex photonic architectures in soft materials.