The role of boundaries in 2D active nematics

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PART 1: NON-TECHNICAL SUMMARY Active matter seeks to describe materials in which chemical energy is consumed at the nanoscale resulting in motion at the macro scale. Examples include the motion of living cells. Recent theories suggest that the motions of living cells are constrained by physical laws to certain characteristic behaviors, and these same theories raise the intriguing possibility that it is possible to engineer new materials with functionalities that heretofore are only found in living organisms. Currently, a lack of quantitative experiments to test theory is hampering progress. This proposal seeks to rectify this imbalance by providing quantitative comparison between theory and experiment in confined two-dimensional active liquid crystals. These tests of theory and discovery of new phenomena will propel the field forward leading to the creation of novel materials, such as self-organizing engines and self-pumping fluids. PART 2: TECHNICAL SUMMARY Active matter research is at the forefront of the field of soft matter, but a lack of quantitative experiments to test theory is hampering progress. This proposal seeks to rectify this imbalance. Experimental studies of confined 2D active nematic liquid crystals will be performed with the goal to elucidate the role of boundary conditions in influencing structure and dynamics. A model system, extensile microtubule bundles, will be employed because of their relative simplicity and high degree of controllability. One thrust will be to establish the microscopic mechanism by which microtubule bundles extend and produce flow. This will be accomplished using combined fluorescence and second harmonic generation microscopy. A second thrust will be to investigate the function of boundary conditions on active nematics by creating a wide variety of confined structures and quantitatively measure the quantities necessary to compare theory and experiment. This will be accomplished using photolithographic and microfluidic manufacturing methods and quantitative light microscopy. A third thrust will be to compare experiment to theory using finite element computation and a fourth thrust will be to engineer soft machines based on confined active nematics that self-organize to perform work, such as pumping of fluids.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.