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      Active Brownian motion tunable by light

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      Author
      Buttinoni, I.
      Volpe, G.
      Kümmel, F.
      Volpe, G.
      Bechinger, C.
      Date
      2012
      Source Title
      Journal of Physics Condensed Matter
      Print ISSN
      0953-8984
      Electronic ISSN
      1361-648X
      Publisher
      Institute of Physics Publishing
      Volume
      24
      Issue
      28
      Pages
      284129-1 - 284129-6
      Language
      English
      Type
      Article
      Item Usage Stats
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      Abstract
      Active Brownian particles are capable of taking up energy from their environment and converting it into directed motion; examples range from chemotactic cells and bacteria to artificial micro-swimmers. We have recently demonstrated that Janus particles, i.e.gold-capped colloidal spheres, suspended in a critical binary liquid mixture perform active Brownian motion when illuminated by light. In this paper, we investigate in more detail their swimming mechanism, leading to active Brownian motion. We show that the illumination-borne heating induces a local asymmetric demixing of the binary mixture, generating a spatial chemical concentration gradient which is responsible for the particles self-diffusiophoretic motion. We study this effect as a function of the functionalization of the gold cap, the particle size and the illumination intensity: the functionalization determines what component of the binary mixture is preferentially adsorbed at the cap and the swimming direction (towards or away from the cap); the particle size determines the rotational diffusion and, therefore, the random reorientation of the particle; and the intensity tunes the strength of the heating and, therefore, of the motion. Finally, we harness this dependence of the swimming strength on the illumination intensity to investigate the behavior of a micro-swimmer in a spatial light gradient, where its swimming properties are space-dependent. © 2012 IOP Publishing Ltd.
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      http://hdl.handle.net/11693/21394
      Published Version (Please cite this version)
      http://dx.doi.org/10.1088/0953-8984/24/28/284129
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