Researchers hoping to understand how liquid crystal’s unique properties can be harnessed in the next generation of advanced materials and photonic devices have shown how to tie the material into knots.
Using a miniature Möbius strip made from silica particles, University of Warwick scientists literally tied liquid crystals in knots, by modifying the alignment of the long, thin, rod-like molecules that line up to all point in the same direction.
The modification was done by simulating the adding of a micron sized silica particle, or colloid, to the liquid crystal. That disrupts the liquid crystal molecules’ orientation.
Colloid Möbius Strips
A colloid, for instance, shaped like a sphere will make the liquid crystal molecules align perpendicular to the surface of the sphere, like a spiny starfish’s spikes.
By using a theoretical model, the scientists took this principle and applied it to colloids which have a knotted shape in the form a Möbius strip. They found that a Möbius strip with one only twist does not form a knot. But with three, four or five twists it becomes a trefoil knot, which is like an overhand knot with the ends joined together, a Solomon’s knot or a cinquefoil knot respectively.
Adding the specially designed knotted particles forces the liquid crystal to take on the same structure, creating a knot in the liquid crystal.
New Metamaterials and Photonic Devices
“Recently it has been demonstrated that knots can be created in a variety of natural settings including electromagnetic fields, laser light, fluid vortices and liquid crystals,” said Assistant Professor Gareth Alexander of Warwick.
“These knots are more intricate than those in your shoelaces, since it is the entire continuous material, and not just a piece of string, that is knotted. Our research extends this previous work to apply to liquid crystal, the substance we use every day in our TVs, smartphones and computer screens.”
“We are interested in this as creating and controlling these intricate knotted fields is an emergent avenue for the design of new metamaterials and photonic devices,” he adds.
Knots and nonorientable surfaces in chiral nematics Thomas Machon and Gareth P. Alexander PNAS August 12, 2013 doi: 10.1073/pnas.1308225110