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SUMMARY:The Five S's: Chemical Swimming\, Sailing\, Surfing\, Squirming an
 d Swarming - Brady\, J (CALTECH (California Institute of Technology))
DTSTART:20130626T080000Z
DTEND:20130626T084500Z
UID:TALK45929@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The design of nanoengines that can convert stored chemical ene
 rgy into motion is an important challenge of nanotechnology\, especially f
 or engines that can operate autonomously. Recent experiments have demonstr
 ated that it is possible to power the motion of nanoscale and microscale o
 bjects by using surface catalytic reactions -- so-called catalytic nanomot
 ors. The precise mechanism(s) responsible for this motion is(are) still de
 bated\, although a number of ideas have been put forth. Here\, a very simp
 le mechanism is discussed: A surface chemical reaction creates local conce
 ntration gradients of the reactant (the fuel) and product species. As thes
 e species diffuse in an attempt to re-establish equilibrium\, they entrain
  the motor causing it to move. This process can be viewed either as osmoti
 c propulsion or as self-diffusiophoresis. The simplest way to break symmet
 ry and achieve motion is by an asymmetric reactivity on the motor surface.
  The mathematical description of suc h motion is analogous to that used to
  describe the swimming of microorganisms\, hence the name 'chemical swimmi
 ng.' However\, symmetry can also be broken by the motor's shape and\, even
  for uniform reactivity\, propulsion can be achieved -- 'chemical sailing.
 ' A motor particle at an air-water interface can change the local concentr
 ation of surface-active agents and propel itself -- 'chemical surfing.' An
 d even local variations of hydrodynamic mobility and interactive potential
  between the motor and the fuel can lead to net motion\, a form of 'chemic
 al squirming.' The implications of these mechanisms on the attainable prop
 ulsive speeds as a function of reaction rate and fuel concentration will b
 e discussed and compared with Brownian dynamics simulations. It will also 
 be shown that chemically active particles can attract or repel each other 
 through long-range 'Coulomb-like' interactions. And suspensions of active 
 particles can exhibit Debye-like screening leading to 'chemical swarming.'
 \n
LOCATION:Seminar Room 1\, Newton Institute
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