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In this talk I will analyze the basic physical mechanisms that control the collective behavior of two kinds of colloidal particles that move in a liquid medium. On the one hand, confined magnetic colloids can rectify their motion when actuated with a rotating magnetic field, acting as a ydrodynamic conveyor belt. Self assembled chains of rotors propel faster than individual ones, until reaching a saturation speed at distances where induced-flow additivity vanishes. On the other hand, the development of Janus colloids has opened the possibility to create synthetic microrobots that can move due to the chemical reacions they catalyze on their heterogeneous surfaces. The motion of chemically powered colloids is intricate because the chemically active colloids perturb the spatial distribution of the chemical species and also the state of motion of the solvent. As a result, suspensions of chemically active colloids are characterized by long range, non-equilibrium interactions. These dynamic interactions have a strong impact in the collective behavior of these suspensions.
I will describe the analogies and specificities in the hydrodynamic coupling that characterize these two types of systems and the different structures they spontaneously form.
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