Manipulation of small particles at solid liquid interface: light driven diffusioosmosis.
The strong adhesion of sub-micron sized particles to surfaces is a nuisance, both for removing contaminating colloids from surfaces and for conscious manipulation of particles to create and test novel micro/nano-scale assemblies. The obvious idea of using detergents to ease these processes suffers from a lack of control: the action of any conventional surface-modifying agent is immediate and global. With photosensitive azobenzene containing surfactants we overcome these limitations. Such photo-soaps contain optical switches (azobenzene molecules), which upon illumination with light of appropriate wavelength undergo reversible trans-cis photo-isomerization resulting in a subsequent change of the physico-chemical molecular properties. In this work we show that when a spatial gradient in the composition of trans- and cis- isomers is created near a solid-liquid interface, a substantial hydrodynamic flow can be initiated, the spatial extent of which can be set, e.g., by the shape of a laser spot. We propose the concept of light induced diffusioosmosis driving the flow, which can remove, gather or pattern a particle assembly at a solid-liquid interface. In other words, in addition to providing a soap we implement selectivity: particles are mobilized and moved at the time of illumination, and only across the illuminated area.
Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany.
David
D
Feldmann
A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31 Leninsky Prospect, 119071 Moscow, Russia.|Department of Physics, M. V. Lomonosov Moscow State University, 119991 Moscow, Russia.
Salim R
SR
Maduar
Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany.
Mark
M
Santer
Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany.
Nino
N
Lomadze
A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31 Leninsky Prospect, 119071 Moscow, Russia.|Department of Physics, M. V. Lomonosov Moscow State University, 119991 Moscow, Russia.|DWI-Leibniz Institute for Interactive Materials, RWTH Aachen, Forckenbeckstraße 50, 52056 Aachen, Germany.
Olga I
OI
Vinogradova
Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany.
Svetlana
S
Santer