Six colloid particles entangled by two unlinked defect loops. Image courtesy of U. Tkalec.
“For the first time, knot formation has been fully controlled and rewired inside liquid crystals.” – Uroš Tkalec
From tying shoes laces, to knitting a jumper to securing a boat, knots are ubiquitous and important in many aspects of everyday life. Knots are also of interest scientifically. Knots have been engineered to inhibit enzymes crucial in infectious diseases (doi:10.1039/B801667D). Semi-flexible polymer chains can be made to form a figure of eight (doi:10.1039/C0SM00290A), while pseudo knots in helical chains can result in stable entanglements that can be built and destroyed (doi:10.1039/B719234G). Even chocolate can be formed in such a way that it is flexible enough to be tied in knots or coiled into a spring (doi:10.1039/B518021j).
Uroš Tkalec from the Jožef Stefan Institute in Slovenia and coworkers have taken the study of knots one step further. In their paper, recently published in Science, the group used laser tweezers to manipulate liquid crystal-colloid mixtures forming knots and links.
When added to a liquid crystal, colloid particles disrupt the crystal ordering creating microscopic topological defect loops. Tkalec manipulated these defects loops using laser tweezers to create loops and knots of arbitrary complexity. Knots demonstrated in the paper include the trefoil, pentafoil and the granny knot.
“The knots and links created here are a rare, potential implementation of mathematical knot theory”- says Tkalec. These knots have potential applications in soft photonic materials, for the control of light in optical liquid crystal microcircuits. Tkalec suggests that their results may also be of relevance in understanding non-trivial topological entities in a number of soft matter systems such as polymers, DNA and proteins.
