| 1. |
- Cai, Tao, et al.
(författare)
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An efficiently tunable microring resonator using a liquid crystal-cladded polymer waveguide
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:12, s. 121109-
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Tidskriftsartikel (refereegranskat)abstract
- An electrically tunable polymer microring resonator of large tunability and low applied voltage is demonstrated using active liquid crystal (LC) cladding. A large tuning range of 0.73 nm is achieved due to more homogenous LC molecular alignment and enhanced interaction of the light with the LC cladding in the simplified polymer waveguide structure. The operating voltage decreases to 10 V with a threshold of only 3 V by the utilization of interdigital electrodes.
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| 2. |
- Liu, Qingkun, et al.
(författare)
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Large-area bulk self-assembly of plasmonic nanorods in nematic liquid crystal via surface-mediated alignment
- 2013
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Ingår i: Optical Materials Express. - 2159-3930 .- 2159-3930. ; 3:11, s. 1918-1924
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we introduce a novel method to organize gold nanorods (GNRs) on a large scale by means of nematic lyotropic liquid crystal (LC) and surface-induced bulk alignment. LC is unidirectionally aligned via surface-treatment, and then gets GNRs organized with a negative order parameter in bulk through elastic force. The self-assembled GNRs (with a considerable high concentration of about 6 wt%) in LC exhibit a strong polarization-dependent localized surface plasmon resonance (LSPR). Polarized optical microscopic imaging, polarization-dependent extinction and scattering spectra of LSPR are utilized to characterize the spatial orientation of GNRs. This method is compatible with the state-of-the-art LC display technique and allows for large-scale fabrication of optical metamaterials, plasmonic polarizers comprised of self-aligned anisometric nanoparticles with extremely low cost.
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| 3. |
- Liu, Qingkun, et al.
(författare)
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Measurement of viscosity of lyotropic liquid crystals by means of rotating laser-trapped microparticles
- 2011
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Ingår i: Optics Express. - 1094-4087. ; 19:25, s. 25134-25143
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Tidskriftsartikel (refereegranskat)abstract
- We describe a simple microrheology method to measure the viscosity coefficients of lyotropic liquid crystals. This approach is based on the use of a rotating laser-trapped optically anisotropic microsphere. In aligned liquid crystals that have negligible effect on trapping beam's polarization, the optical torque is transferred from circularly polarized laser trapping beam to the optically anisotropic microparticle and creates the shear flow in the liquid crystalline fluid. The balance of optical and viscous torques yields the local effective viscosity coefficients of the studied lyotropic systems in cholesteric and lamellar phases. This simple yet powerful method is capable of probing viscosity of complex anisotropic fluids for small amounts of sample and even in the presence of defects that obstruct the use of conventional rheology techniques.
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| 4. |
- Liu, Qingkun, et al.
(författare)
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Plasmonic Complex Fluids of Nematiclike and Helicoidal Self-Assemblies of Gold Nanorods with a Negative Order Parameter
- 2012
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 109:8, s. 088301-
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Tidskriftsartikel (refereegranskat)abstract
- We describe a soft matter system of self-organized oblate micelles and plasmonic gold nanorods that exhibit a negative orientational order parameter. Because of anisotropic surface anchoring interactions, colloidal gold nanorods tend to align perpendicular to the director describing the average orientation of normals to the discoidal micelles. Helicoidal structures of highly concentrated nanorods with a negative order parameter are realized by adding a chiral additive and are further controlled by means of confinement and mechanical stress. Polarization-sensitive absorption, scattering, and two-photon luminescence are used to characterize orientations and spatial distributions of nanorods. Self-alignment and effective-medium optical properties of these hybrid inorganic-organic complex fluids match predictions of a simple model based on anisotropic surface anchoring interactions of nanorods with the structured host medium.
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| 5. |
- Liu, Qingkun, et al.
(författare)
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Self-Alignment of Dye Molecules in Micelles and Lamellae for Three-Dimensional Imaging of Lyotropic Liquid Crystals
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:12, s. 7446-7452
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Tidskriftsartikel (refereegranskat)abstract
- We report alignment of anisotropic amphiphilic dye molecules within oblate and prolate anisotropic micelles and lamellae, the basic building blocks of surfactant-based lyotropic liquid crystals. Absorption and fluorescence transition dipole moments of these dye molecules orient either parallel or orthogonal to the liquid crystal director. This alignment enables three-dimensional visualization of director structures and defects in different lyotropic mesophases by means of fluorescence confocal polarizing microscopy and two-photon excitation fluorescence polarizing microscopy. The studied structures include nematic tactoids, Schlieren texture with disclinations in the calamitic nematic phase, oily streaks in the lamellar phase, developable domains in the columnar hexagonal phase, and various types of line defects in the discotic cholesteric phase. Orientational three-dimensional imaging of structures in the lyotropic cholesterics reveals large Burgers vector dislocations in cholesteric layering with singular disclinations in the dislocation cores that are not common for their thermotropic counterparts.
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| 6. |
- Liu, Qingkun, et al.
(författare)
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Self-Alignment of Plasmonic Gold Nanorods in Reconfigurable Anisotropic Fluids for Tunable Bulk Metamaterial Applications
- 2010
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 10:4, s. 1347-1353
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 7. |
- Liu, Qingkun, et al.
(författare)
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Switchable polarization-sensitive surface plasmon resonance of highly stable gold nanorods-liquid crystals composites
- 2011
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Ingår i: Optoelectronic Materials and Devices VI. - Washington, D.C. : SPIE. - 9780819489616
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Konferensbidrag (refereegranskat)abstract
- In this work, we demonstrate the bulk self-alignment of gold nanorods (GNRs) dispersed in lyotropic nematic liquid crystals (LCs) with high optical absorption coefficient at the surface plasmon resonant wavelength. The polymer-coated GNRs which show spontaneous long-range orientational ordering along the director of LC host exhibit long-term stability as well as high concentration. External magnetic field and shearing allow for alignment and realignment of the orientation of gold nanorods by changing the director of the liquid crystal matrix. This results in a switchable polarization-sensitive surface plasmon resonance exhibiting stark differences from that of the same nanorods in isotropic fluids. The devise-scale bulk nanoparticle alignment may enable optical metamaterial mass production and control of surface plasmon resonance of nanoparticles.
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| 8. |
- Wang, Nan, et al.
(författare)
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Electrically controllable self-assembly for radial alignment of gold nanorods in liquid crystal droplets
- 2015
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Ingår i: Optical Materials Express. - 2159-3930 .- 2159-3930. ; 5:5, s. 1065-1070
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the dispersion and alignment of gold nanorods in 5CB liquid crystal droplets in silicon oil with a radial director structure. This biphasic system shows that the nanorods are stabilized against phase boundary driven aggregation. The radial alignment of the droplets can be further controlled by electric field. This method is potentially useful for the fabrication of hybrid nanostructured materials, such as plasmonic polymer dispersed liquid crystals and self-assembly-based devices; it could also be extended for use with magnetic, semi-conducting, or up-conversion nanoparticles.
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