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Optically directed assembly and motion of particles : a new route for active matter - Delphine Coursault

University of Chicago, USA.

Organization of matter into well-controlled ordered structures is one of the main pursuits of material science especially in nanoscience for applications in nanophotonics. Top-down techniques such as e-beam or focused ion beam lithography and bottom-up ones such as self-assembly are widely used to create static ordered micro/nanostructures. However, the research agenda is now shifting towards achieving tunable, switchable or nonlinear functionalities, which requires dynamic or reconfigurable structures. To achieve this goal, the next generation of optical tweezers coupled with spatial light modulator offers tremendous opportunities.

It is known that the light scattered by (micro)particles can be strong enough to generate significant forces on neighboring ones, and have a spatial structure suitable to trap and localize them. This phenomenon is known as optical binding. It has been recently applied to direct the assembly of spherical metal nanoparticles into optically-bonded supra-crystals. I will present our current investigation on the versatility of optical matter, created by the directed assembly of (non spherical) nano and microparticles in a focused laser beam.

I will first demonstrate that the interactions between particles can be strong enough to lead to extended optical matter that is stable and controllable vs. Brownian noise in solution. Second, the dynamics of optical matter systems can exhibit correlated motion even far from the center of the optical trap. I will then demonstrate that under certain conditions that particles can be “active” and constrain (compress) their surroundings into a non-equilibrium state. This behavior indicates that active optical matter can do work on it surroundings in a manner similar to molecular motors in biology.


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