WPI-AIMR Math Unit

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1st Math Mate Seminar

Date：5/16/2012 Wed.　10:30～12:00
Place：WPI-AIMR Main Building 2F　Seminar Room

Speaker: Dr. Mihail Popescu
Affiliation: Ian Wark Research Institute, University of South Australia
Title: Chemically Active Colloids as Particle Carriers.

【Abstract】

　The reduction in length scales brought about by "lab-on-a-chip"
applications has raised a number of challenging issues. One of them is how to enable small objects to perform autonomous, directional motion (so-called self-propulsion) in a liquid environment. This is a difficult task because for particles of micron scale or below viscous and surface forces dominate the effects of inertia and thus the macro-scale mechanisms of propulsion based on imparting momentum to the fluid cannot be simply scaled down [1-3].

　A promising approach is that of employing catalytically activated chemical reactions to extract ``chemical'' free energy from the surrounding liquid environment and to transform it into mechanical energy (motion of microparticles), resembling the way in which biological molecular motors function. One class of mechanisms to achieve this builds on concepts borrowed from classic phoresis, where the motion of particles is "driven" by externally maintained gradients of some thermodynamic field through surface interactions acting within thin interfacial regions around the particles [4]. The basic idea behind self-phoresis is that of using micron-sized particles partially covered by a catalyst, which activates a chemical reaction in the surrounding liquid, such that concentration gradients of product and reactant molecules along the surface of the particle are "self-generated" [5,6].

　In this talk I will discuss the self-diffusiophoretic motion of a chemically active particle of spheroidal (prolate or oblate) shapes (which are experimentally relevant) [7]. I will then address some peculiar aspects of self-diffusiophoresis in the context of potential application of such active particles as carriers at the micro-scale. A simple model for a carrier-cargo system is that of a chemically active spherical-particle connected by a thin rigid rod to a chemically-inert cargo particle. 　Adopting the standard theory of diffusio-phoresis, the velocity of the carrier-cargo composite can be analytically derived. The results show that the performance of the carrier, i.e., the resulting velocity of the composite system, strongly depends on the orientation of the link, which is a paradigmatic consequence of self-phorestic motion [8].

【References】
1. E. Lauga E. and T.R. Powers, Rep. Prog. Phys. 72, 096601 (2009).
2. R.F. Ismagilov et al., Angew. Chem., Int. Ed. 41, 652 (2002).
3. S.J. Ebbens and J.R. Howse, Soft Matter 6, 726 (2010).
4. J.L. Anderson, Ann. Rev. Fluid Mech. 21, 61 (1989).
5. R. Golestanian, T. B. Liverpool, and A. Ajdari, Phys. Rev. Lett. 94,
220801 (2005).
6. B. Sabaas and U. Seifert, J. Chem. Phys. 136, 064508 (2012).
7. M.N. Popescu, S. Dietrich, M. Tasinkevych, and J. Ralston, Eur.
Phys. J. E 31, 351 (2010).
8. M.N. Popescu, S. Dietrich, and M. Tasinkevych, EPL 95, 28004 (2011).

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1st Math Mate Seminar

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