![]() ![]() Flowing like liquids, they are composed of anisotropic molecules and exhibit long range orientational order as well as varying degrees of positional order ( 1– 4). Potential applications include modeling thermodynamic systems with anisotropic polarization-controlled potential wells, producing optically tunable photonic crystals, and fabricating light-controlled nano- and micropumps.Īnisotropic fluids have properties intermediate between those of liquids and solid crystals ( 1). ![]() 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. Anisotropic particle dynamics in the trap varies with laser power because of the anisotropy of both viscous drag and trapping forces. This control allows the optical forces to be reversed and cause the particle to follow a prescribed trajectory. Trapping forces in the beam's lateral plane mimic the corona and are polarization-controlled. The laser beam can trap such particles not only at their center but also at the high-index corona. This distortion produces a refractive index “corona” around the particles that depends on their surface characteristics. Immersed colloidal particles modify the fluid's ordered molecular structures and locally distort its optic axis. We demonstrate that laser beams in these fluids can generate anisotropic optical trapping forces, even for particles larger than the trapping beam wavelength. Optical trapping is potentially a powerful technique in the fundamental studies and applications of anisotropic fluids. Anisotropic fluids are widespread, ranging from liquid crystals used in displays to ordered states of a biological cell interior.
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