Seminarium Fizyki Materii Skondensowanej

Synthetic micro-motors which can move cargo in a well controlled waythrough a liquid environment are of signi cant interest for applicationssuch as targeted drug delivery, biosensing, or shuttle-transport of livingcells. One promising approach is to use catalytically active Januscolloidal particles as model micro-motors. Due to an asymmetric decorationof their surface with a catalyst, which promotes a speci c chemicalreaction in the surrounding liquid, concentration gradients of thereaction products develop along the surface of the particle. Depending onthe systems, various self-propulsion mechanisms emerge, such as bubblepropulsion, self-electrophoresis, or self-diusiophoresis. In this talk weconsider only the last mechanism, i.e. self-propulsion due toself-generated electrically neutral solute gradients. First, we discussthe self-diusiophoretic motion of a spheroidal particle, which is coveredby a catalyst over a cap-like region centered at one of the poles of theparticle. We describe how theself-phoretic velocity depends on the aspect ratio of the polar and theequatorial diameters of the particle and on the fraction of the particlesurface contributing to the chemical reaction. Next we show that suchparticles can be used as micro-carriers. As a simple model for acarrier-cargo system we consider a catalytically active particle connectedby a thin rigid rod to a catalytically inert cargo particle. We show thatthe velocity of the composite strongly depends on the relative orientationof the carrier-cargo link. Accordingly, there is an optimal con gurationfor the linkage. The subtlety of such carriers is underscored by theobservation that a spherical particle completely covered by catalyst,which is motionless when isolated, acts as a carrier once attached to acargo.