ChaikinLab Condensed Matter Physics





    "Crystals" on Curved Surface
    The research is centered on using colloidal particles to understand basic questions in condensed matter physics. Colloids are microscopic particles which are dispersed in a fluid, for instance water or oil. Many common household products - for example milk, coffee, and sunscreen - are colloidal in nature. For physicists, colloids are interesting because they are small enough to reach thermal equilibrium in reasonable times (unlike baseballs), and large enough that they can be seen with an optical microscope (unlike atoms). This makes colloids ideal for studying basic questions about how matter behaves under various conditions. In particular, we look at a 2D system of charged micron-sized particles, dispersed in oil, which bind to a fluid interface. Our research questions include: how do these particles interact? How can we describe the phase behavior of an ensemble of similar particles? When the fluid interface is curved, how does the system balance competing energetic, entropic and topological constraints? Does the presence of curvature fundamentally change the phase behavior of the material? Is there a low-temperature ordered phase? What does it even mean for a structure on a curved surface (like a sphere) to be "ordered"?
    Roller Flow Instability
    We have identified a new kind of flow instability in a system of rolling colloidal particles. When a colloidal particle rotates near a surface, rolling leads to translational motion, as well as very strong flows around the particle, even quite far away. These large advective flows strongly couple the motion of neighboring particles, which give rise to strong collective effects in groups of rolling particles. It is these collective effects which cause the formation of a shock front, that then becomes unstable.
    We study this flow instability using weakly magnetic colloids driven by a rotating magnetic field. When driven, an initially uniformly-distributed strip of microrollers evolves into a shock structure, which then becomes unstable, emitting fingers with a well-defined wavelength. In collaboration with Blaise Delmotte and Aleksander Donev, we use large-scale three-dimensional simulations in tandem with our experiments to study the instability dynamics. We find that the instability wavelength is controlled not by driving torque or fluid viscosity, but a geometric parameter: the microroller’s distance above the container floor. Furthermore, we find that the instability dynamics can be reproduced using only one ingredient: hydrodynamic interactions near a no-slip boundary.

Assembly of Droplets Using DNA glue

Self Replication of DNA nanostructures

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Active Swimmers

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DNA origami swimmers

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