Active colloids with tunable interactions in liquid crystals

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Nontechnical abstract:Mankind is increasingly dependent on technologies of transportation. Over centuries, the thrust has been on development of macroscopic devices such as cars, planes, ships that are larger than the human beings. The new challenge is to develop miniature systems that could rectify the energy of environment into directed motion at the scale of micrometers. In the future, these micromachines are expected to interact with biological tissues and individual cells, serve as elementary units of soft microrobots, deliver microscopic quantities of drugs or other useful chemicals, work as energy harvesters, responsive actuators, microscale mixers and separators. Electric field is considered as one of the most effective means in powering the transport of matter at microscale. Most of the studies of microdynamics are performed for an isotropic environment, such as water, which does not provide a clear sense of direction for electrically powered microsystems. The goal of the project is to learn how one can control dynamics of microparticles by anisotropic fluids, with properties that depend on the direction in space. These fluids are known as liquid crystals. Anisotropy of liquid crystals under the action of the electric field is already used in informational displays of modern computers, smartphones and TV sets. The project will explore how to use liquid crystals as a medium that enables and commands dynamics and interactions of microparticles. The project will advance the knowledge of mechanisms defining dynamics of soft matter at microscopic scales and potentially contribute to the technologies of future micromachines. Technical abstract:Collective out-of-equilibrium spatiotemporal dynamics of microscopic particles in the so-called active matter is a fascinating area of intense studies. Depending on the type of interactions, active matter develops various scenarios of behavior, from coordinated collective unidirectional motion to turbulent-like flows. The project will explore how the electric field controls dynamics of colloidal particles and their interactions at microscale, using methods such as optical microscopy, confocal microscopy and particle velocimetry. The project will answer a question whether and how the seemingly chaotic dynamics of active matter can be controlled by an ordered environment of a liquid crystal. The potential transformative value is in understanding the mechanisms by which the orientational order can command interactions and collective motion in ensembles of electrically powered active particles. The orientational order of the proposed LC environment imposes long-range anisotropic elastic and hydrodynamic interactions and propulsion modes that are absent in isotropic fluids. The project will advance the knowledge of electro-hydrodynamics of LCs and colloids, physics of out-of-equilibrium active matter. Application of already tested methods such as three-dimensional confocal microscopy, particle imaging velocimetry, patterned photo-alignment and electro-optics will ensure that the new knowledge is based on a solid experimental background. The project will provide a new platform to design and control ensembles of active particles, which has the potential for enormous societal benefits in areas ranging from existing technologies (such as improved electrophoretic displays) to the technologies of the future, which would exploit the unique ability of active colloids to transduce energy from the environment into systematic movement, to control the flow of matter, to serve as important elements of micromachines. The project will educate a new and diverse generation of scientists with fundamental and technological expertise in soft and active matter.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.