Hydrodynamic Crystals: Structural Evolution in Confined Suspension Flows

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0931504BlawzdziewiczUnderstanding of collective hydrodynamic phenomena in microconfined suspension flows is crucial in diverse research fields that range from dynamics of bacterial colonies to microfluidics. Such phenomena, however, are far from being understood. To elucidate collective hydrodynamics of particulate systems we propose to investigate the evolution of strongly confined ordered suspensions in parallel wall channels. We will study two kinds of systems: particle arrays interacting only via hydrodynamic forces, and flow driven colloidal crystals where particle ordering stems from potential and hydrodynamic forces. Our preliminary studies of flow driven ordered particle arrays reveal that these systems show wave propagation, sudden rearrangements of particle lattice, order disorder transitions, and fingering instabilities. Using numerical, experimental and theoretical methods, we will investigate hydrodynamic mechanisms that produce this rich dynamical behavior. Insights from our studies will shed new light on basic questions of particulate flows, will be applicable to other ordered dissipative systems, and will also suggest new strategies for practical applications (e.g., multidrop microfluidic devices and particulate coating flows). The proposed numerical simulations will be performed using our novel Stokesian dynamics algorithm that is accurate and highly efficient. The experimental part will consist in assembling regular 2D particle arrays using holographic optical tweezers, and observing changes in suspension microstructure using confocal microscopy. Our theoretical investigations will involve Fourier analysis of displacement waves in regular particle arrays and an effective medium approach to describe the evolution and instabilities of the arrays.Intellectual Merit: The intellectual value of our proposed research is both fundamental and practical. We will study an entirely new class of hydrodynamic phenomena in creeping particulate flows. Our results will be relevant to nonlinear physics (including dynamics of complex fluids, structural evolution in dusty plasma, and collective motion of flux vortices in superconductors). Our results will also have significant impact on engineering applications, especially in microfluidics. Emerging multidrop microfluidic applications include tunable optical devices, high throughput lab-on-chip assays, and manufacturing microstructured materials. Understanding hydrodynamic mechanisms governing suspension structure under strong confinement conditions is key in such applications, and our proposed research will uncover such mechanisms.Broader Impact: This project will provide educational and research opportunities for graduate, undergraduate and high school students. Graduate and undergraduate students will present their work at New England Complex Fluids Workshops and at national scientific meetings. Students from under represented groups will be recruited through the STARS (Science, Technology and Research Scholars) program at Yale. The PIs will support K-12 education in Greater New Haven by serving as judges in New Haven science fairs. Interdisciplinary significance of our project consists in obtaining results that will be used in physics of pattern formation, physical chemistry, and microfluidic technology. Insights from our research will also be applicable to biological sciences in investigations involving collective hydrodynamic effects, e.g., in studies of bacterial motion. Software for particle tracking and some of the Stokesian dynamics codes will be disseminated through free websites. This research also involves international collaboration.