Pushing, pulling and twisting liquid crystal systems: exploring new directions with laser manipulation

Abstract

Optical tweezers are exciting tools with which to explore liquid crystal (LC) systems; the motion of particles held in laser traps through LCs is perhaps the only approach that allows a low Ericksen number regime to be accessed. This offers a new method of studying the microrheology associated with micrometre-sized particles suspended in LC media-and such hybrid systems are of increasing importance as novel soft-matter systems. This paper describes the microrheology experiments that are possible in nematic materials and discusses the sometimes unexpected results that ensue. It also presents observations made in the inverse system; micrometre-sized droplets of LC suspended in an isotropic medium.

Optical Manipulation of a Liquid Crystal (LC) Microdroplet by Optical Force

“…[74] In another study, it was reported that LC droplets were used to fabricate micrometer-sized cylinders that rotated in a circularly polarized optical trap to measure the viscosity of composite LC. [33] In the same study, the rotation of the LC microdroplets was used to measure host media such as heavy water. [33] LC is a soft but brilliant material that responds to stimuli by adjusting its chemical and physical properties.…”

“…[33] In the same study, the rotation of the LC microdroplets was used to measure host media such as heavy water. [33] LC is a soft but brilliant material that responds to stimuli by adjusting its chemical and physical properties. The soft microactuator using an LC microdroplet is more flexible than a solid microactuator.…”

“…[11,24] In addition to optical trapping of a solid, trapping of a soft material such as glycine, [25] oil droplets, [26] water droplets, [27] oleic acid droplets, [28] organic solvents, [29,30] and LCs have been studied. [31] The optical properties of LC have enabled its use in various fields and applications such as LCD technology, [32,33] microresonator, [34] LC-based sensors, [35][36][37][38][39] tuneable lenses, [1] and others. In the context of LC, optical manipulation has also helped to understand the interaction between light and LC.…”

Droplet Manipulations in Two Phase Flow Microfluidics

“…By changing the angle at which the collimated beam enters the objective the focal spot is translated laterally, while changing the incoming beam to slightly diverging or converging translates the focal spot axially. The technique is not limited to just water of course, but can for instance also manipulate liquid crystals [77], as long as there is a gradient in refractive index. To be able to manipulate multiple droplets or particles, multiple individually changeable beam wave fronts are required.…”

New frontiers in anisotropic fluid–particle composites

“…Opening the final session of the conference, Helen Gleeson [12] showed how optical traps can be used to manipulate particles in liquid crystals to perform micro-rheology experiments to provide information about the viscosity coefficient ratios of the liquid crystal material and the trap stiffness. Laser tweezers can also be a tool to manipulate liquid crystal droplets, leading to a range of phenomena, including all-optical switches and opto-mechanical transducers ( figure 7).…”