(678a) Soluto-Inertial Phenomena: Designing Long Range, Long-Lasting, Surface-Specific Colloidal Interactions

Equilibrium interactions between
particles in aqueous suspensions are limited to distances less than 1 µm. Here,
we describe a versatile concept to design and engineer non-equilibrium
interactions whose magnitude and direction depends on the surface chemistry of
the suspended particles, and whose range may extend over hundreds of microns
and last thousands of seconds. The mechanism described here relies on
diffusiophoresis, in which suspended particles migrate in response to gradients
in solution. Three ingredients are involved: a soluto-inertial ÔbeaconÕ
designed to emit a steady flux of solute over long time scales; suspended
particles that migrate in response to the solute flux, and the solute itself,
which mediates the interaction. We demonstrate soluto-inertial interactions
that extend for nearly half a millimeter, last for tens of minutes, and which
are attractive or repulsive, depending on the surface chemistry of the
suspended particles. Experiments agree quantitatively with scaling arguments
and numerical computations, confirming the basic phenomenon, revealing design
strategies, and suggesting a broad set of new possibilities for the
manipulation and control of suspended particles.

Figure 1:
Long-range soluto-inertial interactions. A soluto-inertial beacon (gray),
initially loaded with a high solute concentration, is placed in a solute- free
suspension. A solute out-flux is established during equilibration, driving
nearby suspended particles into diffusiophoretic migration. The magnitude and
direction of migration depends on interactions between the particle surface and
the solute, depicted here by particles of different surface chemistries (orange
and green) that migrate either up or down the solute gradient. Inset: schematic
radial profile of solute concentration inside and outside of the beacon.