61st Annual Report on Research 2016

Geometric shape and topology of constituent particles can alter many colloidal properties such as Brownian motion, self-assembly, and phase behavior. So far, only single-component building blocks of colloids with connected surfaces have been studied, although topological colloids, with constituent particles shaped as freestanding knots and handlebodies of different genus, have been recently introduced. Under thge support of the PRF funding, we develop a new topological class of colloids shaped as multicomponent links. Using two-photon photopolymerization, we fabricate colloidal microparticle analogues of the classic examples of links studied in the field of topology, the Hopf and Solomon links, which we disperse in nematic fluids that possess orientational ordering of anisotropic rod-like molecules. The surfaces of these particles are treated to impose tangential or perpendicular boundary conditions for the alignment of liquid crystal molecules, so that they generate a host of topologically nontrivial field and defect structures in the dispersing nematic medium, resulting in an elastic coupling between the linked constituents. The interplay between the topologies of surfaces of linked colloids and the molecular alignment field of the nematic host reveals that linking of particle rings with perpendicular boundary conditions is commonly accompanied by linking of closed singular defect loops, laying the foundations for fabricating complex, composite materials with interlinking-based structural organization. Colloidal dispersions are abundant in nature, fundamental science, and technology, with examples ranging from fog and milk to colloidal models of atomic crystals and glasses and colloidal quantum dots used in fabricating the third generation solar cells. Despite the recent progress in exquisite control of geometric shape and topology of constituent colloidal particles, so far only single-component colloidal building blocks have been fabricated or found occurring in nature. We develop multicomponent linked colloidal particles lacking connectivity of their surfaces, with each component behaving as a genus-one colloidal particle itself but being topologically linked with the other components within a colloidal building block. We uncover topological property-defining behavior of such colloidal particles when dispersed in a nematic liquid crystal medium.