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'Boomerangs' and 'trampoline effect' could yield new liquid crystal applications

Posted Jan. 13, 2014

Two recent journal articles by researchers in the Liquid Crystals Institute report new findings on how particles move through a liquid crystal and how boomerang-shaped liquid crystals move through water.

Both studies center on Brownian motion, a physics phenomenon central to Einstein's work more than a century ago. They could lead to future applications in new materials and in medicine, reviewers said.

Brownian motion, a physics phenomenon central to Einstein's work more than a century ago, is the subject of two recent papers by Kent State researchers in the university's Liquid Crystal Institute.

In a Science paper published Dec. 13, 2013, Oleg D. Lavrentovich, Trustees Research Professor, and his co-authors reported a "trampoline effect" when a small particle moved through a liquid crystal. Brownian motion describes particles moving through a fluid and being jostled by molecules of the fluid. The novelty in the Science paper, Lavrentovich said, was to explore whether the particles' motion is any different when the surrounding fluid is a liquid crystal rather than water.

The researchers found that it is. "The difference is very significant; it is like walking on a sidewalk and walking on a trampoline. In the liquid crystal environment, the elastic nature of the molecular orientation makes each step influence the subsequent steps," he said.

Research that has evolved over the past 20 years in this area could lead to liquid-crystal-based systems that would have a technological impact "well beyond traditional applications of LCs in displays," according to a review in Science. Brownian motion controls transport processes in systems ranging from the inside of cells to drying paint, the review noted. The research "hints at new principles" for manipulating these transport processes, the review said.

Other researchers on the paper were from three Ukrainian institutions – the Institute of Physics, the National Technical University of Ukraine, and the Bogolyubov Institute for Theoretical Physics – and the Liquid Crystals Division of Merck, KGaA, Germany.

In research published Oct. 18 in Physics Review Letters, a Kent State group led by Qi-Huo Wei, associate professor of chemical physics, and Jonathan V. Selinger, professor of chemical physics and an Ohio Eminent Scholar, showed that when Brownian particles are boomerang-shaped, they will diffuse differently in liquid compared with spherically or football-shaped particles.t_black2

Boomerang-shaped molecules are an important type of liquid crystal, Wei said.

A review of the paper in Physics pointed to potential future applications in delivering drugs to targeted cells in the body or in new self-assembling materials.

Selinger said that Brownian motion has been studied in many different kinds of applications since Einstein in 1905 used it to show that molecules really exist.

In recent years, researchers have considered how it applies to ellipsoidal, or football-shaped, particles. Taking this a step further and fabricating tiny boomerang-shaped polymeric particles, Wei looked at how their movements through water differ from those of football-shaped particles. The boomerangs pulled to one side, similar to the way a car that needs a wheel alignment does, Selinger said. The researchers called this "biased Brownian motion."