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Download fileExtremely Long-Range Light-Driven Repulsion of Porous Microparticles
journal contribution
posted on 2020-03-10, 15:21 authored by David Feldmann, Pooja Arya, Taras Y. Molotilin, Nino Lomadze, Alexey Kopyshev, Olga I. Vinogradova, Svetlana A. SanterThe
repulsive surface forces, such as electrostatic or steric,
acting between particles explain why they remain well separated in
aqueous electrolyte solutions and are responsible for the stability
of colloidal dispersions. However, the effective range of these interactions
is always well below hundreds of nanometers and typically can be controlled
by advanced manipulations such as tuning the electrolyte concentration
or modifying the particle surface or, in some more specific cases,
via subjecting the suspension to an external electric or magnetic
field. Here we employ solutions with small additives of a photosensitive
ionic surfactant to investigate if a repulsive interaction of microsized
particles sedimented at the solid surface can be remotely controlled
simply by illuminating it with an appropriate wavelength. We show
that interactions of conventional impermeable particles remain practically
unaffected by light, but, in contrast, for porous particles, we observe
a long-range repulsion, several orders of magnitude longer than any
conceivable equilibrium surface force. This repulsion emerges due
to the diffusio-osmotic flow generated near the porous particles that
in this scenario are playing a role of micropumps. The diffusio-osmotic
repulsion of porous particles can be used for a remote control of
their two-dimensional assemblies at the solid wall, and in particular,
we demonstrate that by simply using two different illumination wavelengths
it is possible to reversibly switch the state of porous particle dispersion
from densely packed surface aggregates to a periodic lattice of particles
separated by distances on the order of tens of micrometers.
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Keywords
microsized particles sedimentedimpermeable particlesreversibly switchPorous Microparticlesdiffusio-osmotic flowExtremely Long-Range Light-Driven Repulsionsurface forcesequilibrium surface forcediffusio-osmotic repulsionelectrolyte concentrationillumination wavelengthsparticle surfaceelectrolyte solutionssurface aggregatesparticle dispersion