Manipulation of Disk-Shaped Islands on Freely Suspended Smectic Films and Bubbles Using Optical Tweezers

Pattanaporkratana, Apichart; Park, C. S.; Maclennan, Joseph E.; Clark, Noel A.

doi:10.1080/00150190490510537

Cited by 30 publications

(19 citation statements)

References 7 publications

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“…Islands in the quadrupolar structure also exhibit a well-defined equilibrium separation. When the island separation is altered using optical tweezers [33], the vertical separation S of the −1 defects also changes. At sufficiently large island separation, the quadrupolar symmetry is broken and the structure evolves into two separate dipoles [31].…”

Section: Resultsmentioning

confidence: 99%

Modeling dipolar and quadrupolar defect structures generated by chiral islands in freely suspended liquid crystal films

et al. 2009

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We report a detailed theoretical analysis of novel quadrupolar interactions observed between islands, which are disk-like inclusions of extra layers, floating in thin, freely suspended smectic C liquid crystal films. Strong tangential anchoring at the island boundaries result in a strength +1 chiral defect in each island and a companion −1 defect in the film, these forming a topological dipole. While islands of the same handedness form linear chains with the topological dipoles pointing in the same direction, as reported in the literature, islands with different handedness form compact quadrupolar structures with the associated dipoles pointing in opposite directions. The interaction between such heterochiral island-defect pairs is complex, with the defects moving to minimize the director field distortion as the distance between the islands changes. The details of the inter-island potential and the trajectories of the −1 defects depend strongly on the elastic anisotropy of the liquid crystal, which can be modified in the experiments by varying the material chirality of the liquid crystal. A Landau model that describes the energetics of freely mobile defects is solved numerically to find equilibrium configurations for a wide range of parameters.

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Section: Resultsmentioning

confidence: 99%

Modeling dipolar and quadrupolar defect structures generated by chiral islands in freely suspended liquid crystal films

et al. 2009

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“…As the indices of a typical liquid crystal are relatively high (ordinary index of 1.5 and extraordinary index around 1.7), this seems to reduce possible choices for colloidal materials. Laser tweezers were used to trap and measure forces between polystyrene colloids (n ¼ 1:59) in low-index nematic liquid crystals (35)(36)(37)(38)(39), to switch liquid crystal microdroplets (40,41), to manipulate defects in lyotropic liquid crystals (42), to manipulate islands on freely suspended smectic films (43), to trap and manipulate high-index colloids in the nematic (44) and defects in a nematic liquid crystal (45).…”

Section: Manipulation Of Colloidal Particles In the Nematic Liquid Crmentioning

confidence: 99%

Optical manipulation and self-assembly of nematic colloids: colloidal crystals and superstructures

Muševič

2010

Liquid Crystals Today

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Optical manipulation of colloidal particles in nematic liquid crystals is far more complex than manipulation in water-based colloids. Owing to the long-range nature of the orientational ordering, their elasticity and topological conservation laws, almost any kind of object can be trapped and manipulated in liquid crystals. Furthermore, local heating due to the absorption of light can be used to create microdroplets of the isotropic phase, which interact strongly with colloidal particles. This leads to a broad variety of colloidal assemblies in liquid crystals, which cannot be observed in isotropic solvents: colloidal wires, assembled by entangled topological defects, superstructures in mixtures of large and small colloidal particles and a broad variety of two-dimensional nematic colloidal crystals. In all cases, the colloidal binding energy is several orders of magnitude stronger compared with waterbased colloids. The large variety of colloidal superstructures, which can be assembled in nematic colloids, makes them highly interesting for application in photonic materials.

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“…Anisotropic self-organization in a living cell's interior may play a vital biological function and is readily observed by means of birefringence imaging (15,16). Recently, there has been a growing interest in optical trapping in anisotropic media (17)(18)(19)(20)(21)(22). Laser tweezers can control dynamics of nano-and micro-objects and allow for measurement of colloidal forces (2, 23) mediated by LC elasticity (12,19).…”

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Laser trapping in anisotropic fluids and polarization-controlled particle dynamics

Smalyukh

Kachynski

Kuzmin

et al. 2006

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

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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 polarizationcontrolled. 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.colloids ͉ laser tweezers ͉ liquid crystals ͉ optical trapping ͉ defects

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Manipulation of Disk-Shaped Islands on Freely Suspended Smectic Films and Bubbles Using Optical Tweezers

Cited by 30 publications

References 7 publications

Modeling dipolar and quadrupolar defect structures generated by chiral islands in freely suspended liquid crystal films

Modeling dipolar and quadrupolar defect structures generated by chiral islands in freely suspended liquid crystal films

Optical manipulation and self-assembly of nematic colloids: colloidal crystals and superstructures

Laser trapping in anisotropic fluids and polarization-controlled particle dynamics

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