Roichman Lab

School of Chemistry, Tel Aviv University

Experimental Soft Matter

We are interested in studying the underlying physical processes that govern the mechanics, self-organization, dynamics, and statistics of complex fluids out of thermal equilibrium. Our belief is that by studying in detail many such driven systems we will be able to observe emergent shared characteristics, paving the way for a theoretical description.
We use holographic optical tweezers to manipulate and drive microscopic objects, a variety of optical microscopy techniques to image these objects, and image analysis to study their motion and morphology.

Experimental techniques

Currently, there are five imaging stations in my lab, four microscope based, and one for high-speed imaging. Two of the microscopes are outfitted with HOTs, one operating at 532 nm and one at 1085 nm. We have epiflourescence, spinning disk confocal, DIC, and holographic microscopy setup in the lab as well.

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Statisticl mechanics

We study non-equilibrium statistical mechanics experimentally. One model system that we have studied in detail during the past years is that of colloidal particles rotating in an optical vortex. In the figure the trajectories of many diffusing particles, subjected to an optical vortex trap are plotted. The particles that are within range of the optical trap are drawn to the ring-like trap, and then rotate along the perimeter of the ring.

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Microrheology is a technique to mechanically characterize materials in an economic manner. For this reason it is used extensively in biophysics to study biological materials such as in-vitro cytoskeleton networks and the cytoplasm of live cells. In the past year we have discovered a new regime of mechanical response of complex fluids via microrheology experiments. The length scale relevant for this new type of material response is surprisingly large, for actin networks in is in the range of 2-6 microns.

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