Collaborative Research: Topological Defects and Dynamic Motion of Symmetry-breaking Tadpole Particles in Liquid Crystal Medium

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A fast-growing technology market is related to microactuators: small-scale active devices capable of generating mechanical motion of solids or fluids by converting one form of energy into kinetic energy. Their programmable motion capabilities could influence several applications including sensors, drug delivery, and soft robotics. Manipulating microactuators to operate at a specific position is still challenging. Substantial efforts have been made on using symmetrical colloidal particles of nano- to micro-scale in conventional aqueous mediums as microacutators. This award aims to synthesize asymmetric tadpole particles composed of a spherical head and highly asymmetrical tail features and explore the impacts of multiple asymmetrical features on particle-induced topological defects and controllable motion in anisotropic liquid crystal medium. The project will provide an interdisciplinary platform involving chemistry, physics, and engineering to develop the potential for local targeting, with applications such as drug delivery and bioimaging on specific cells and initiation of site-specific reactions by carrying catalysts. The collaborative nature of this proposal will provide undergraduate students from a predominantly undergraduate institution (PUI) the opportunity to be exposed to very high intensity R1 institutional culture through summer rotations. The proposed outreach efforts will also expand the participation of underrepresented groups. This award will provide fundamental knowledge of how particles’ asymmetric factors affect topological defects, out-of-equilibrium motion, and controllable hydrodynamics in ordered liquid crystal (LC) medium. The proposed research is to determine the relationship between asymmetric parameters of tadpole particles and the morphology of the resulting distorted nematic field. Elucidating this fundamental knowledge is vital to the rational design of chemically patterned surfaces that have featured topological boundary conditions for commanding particle motion. The long and flexible tail of tadpole particles, as compared to spherical or other symmetric particles, can significantly enhance the asymmetric distortion of long-range order anisotropic liquid crystal medium and the capability to encapsulate a second media at the interface, to facilitate a propulsion mechanism for the particle and enable cargo transportation. The degree of freedom in surface modification of SiO2 tails further enhances the manipulation of direction and velocity of particle motion. Through a feedback loop between asymmetric particle synthesis, experimental evidence on its physical morphologies in LC and further engineering motion, interdisciplinary knowledge will be developed to connect the particle design, synthesis and surface chemistry to topological defects and out-of-equilibrium motion in the ordered liquid crystal media.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.