Colloidal Interactions and Collective Behavior in Non-Conservative Optical Force Fields

New York University, New York NY

Investigators

Abstract

****NON-TECHNICAL ABSTRACT**** How do molecular motors coordinate their movements to power our muscles? By what principles do such nanometer-scale machines exploit molecular chaos to do their work? Answers to these questions would not only provide valuable insights into natural systems and processes, but also could provide a basis for developing new technology. This research program seeks these answers through experimental studies on model systems that participate in the same physical processes, but whose motivating forces can be tuned and whose behavior lends itself to detailed analysis. These systems are created from very small microscopic particles (colloidal particles) moving through force fields exerted by computer-designed holograms. The colloidal particles? three-dimensional motions are measured with very high resolution using holographic video microscopy and analyzed using the latest developments in the theory of nonequilibrium statistical physics. Recently, this approach has revealed the existence of Brownian vortexes, noise-driven micromachines that do work even in quiescent force fields. Insights into activation and synchronization of natural and artificial micromachines should emerge from a systematic study of Brownian vortexes created from colloidal spheres and specifically crafted beams of light. The combination of holographic experimental techniques used in this project defines the state of the art in this field. In addition to powering this research program, holographic control over the microscopic world will continue to take center stage in New York University's Scientific Frontiers program, a K-12 educational outreach activity that brings hundreds of New York City schoolchildren to NYU for hands-on laboratory experiences. **** TECHNICAL ABSTRACT**** This experimental program combines holographic optical trapping with holographic video microscopy to probe the statistical physics of individual and interacting colloidal particles moving through non-conservative force fields. Recent developments of optical micromanipulation techniques have created new opportunities to exert precisely controlled forces on microscopically textured systems. Phase gradients in holographically projected traps can give rise to forces and torques that generically violate conservation of mechanical energy. Colloidal particles in phase-enabled optical traps therefore constitute an exceptionally flexible test-bed for new ideas in nonequilibrium statistical physics. The experimental program will exploit new methods of holographic video microscopy to measure the three-dimensional trajectories of optically trapped colloidal particles with nanometer resolution. The holographic optical traps will be designed to optimize both conservative and non-conservative forces. The resulting rich data sets will provide direct insights into the single-particle dynamics, inter-particle interactions, and many-body collective behavior of driven dissipative steady states. Each element of this project, from holographic control of light-induced forces, to synchronization and entropy production in coupled arrays of stochastic heat engines involves the resolution of outstanding scientific and technological questions. The techniques developed for this program, furthermore, will continue to take center stage in New York University's Scientific Frontiers program, a K-12 educational outreach activity that brings hundreds of New York City schoolchildren to NYU for hands-on laboratory tours.