Soluto-inertial phenomena: Designing long-range, long-lasting, surface-specific interactions in suspensions

Abstract

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 nonequilibrium 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 "beacon" 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 and 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.olloidal suspensions and emulsions of 10-nm to 10-μm particles play a central role in a wide variety of industrial, technological, biological, and everyday processes. Everyday goods, including shampoos, inks, vaccines, paints, and foodstuffs as well as industrial products such as drilling muds, ceramics, and pesticides, rely fundamentally on stably suspended microparticles for their creation and/or operation. This incredible versatility derives from the extensive variety of properties (e.g., mechanical, optical, and chemical) attainable in suspension through a generic set of physicochemical strategies (1-4). A proper understanding of the stability and dynamics of suspensions in general thus underpins both fundamental science and technological applications.The properties and performance of suspensions depend preeminently on the effective interactions between particles. The celebrated Derjaguin-Landau-Verwey-Overbeek (DLVO) theory (5-7) balances electrostatic interactions (typically repulsive) between charged colloids-as screened by ions in the surrounding electrolyte-against van der Waals attractions, and successfully predicts the stability, phase behavior, and response of electrostatically stabilized suspensions. Additional (non-DLVO) forces can also be used to stabilize or destabilize colloidal suspensions. Grafted or adsorbed macromolecules provide short-range steric repulsions that stabilize suspended particles against van der Waals-induced flocculation (8-11). By contrast, nonadsorbed macromolecules that remain dispersed in solution introduce entropic depletion attractions whose strength and range is set by the size and concentration of depletants (12, 13). Such depletion interactions scale with thermal energy (k B T), and thus enable tunable and reversible attractions (14, 15). Clever design of shaped or patterned coll...

Diffusiophoretic Focusing of Suspended Colloids

“…Diffusiophoresis (DP) occurs when colloidal particles are driven into motion by solute concentration gradients [1][2][3]. In recent years, interest in DP has surged, particularly in new contexts such as polymer coating [4], membrane fouling [5,6], enhanced transport of particles into or out of dead-end pores [7,8], self-propelled particles [9,10], and the design of long-range "soluto-inertial" interactions in suspensions [11].…”

Targeted assembly and synchronization of self-spinning microgears

“…Their use to design nonequilibrium interactions and control self-assembly remains, however, largely unexplored [19][20][21][22] . We introduce a sequential approach as a means to architect structures, the dynamics of which arise from chemical gradients through diffusiophoretic interactions.…”

Self-Assembly of Colloidal Molecules due to Self-Generated Flow

“…Finally, a recent theoretical proposal are catalytically active colloidal particles that interact through producing or consuming chemicals [19,20]. For simple diffusion the concentration profile of a chemical decays as inverse distance, implying long-range interactions that can be tuned through activity (how chemicals are produced or consumed) and mobility (how particles react to gradients).Here, we implement long-range attractions through hydrodynamic flows coupling suspended particles [21,22]. We report on experiments using spherical ion exchange resin particles sedimented to the negatively charged substrate.…”

“…Here, we implement long-range attractions through hydrodynamic flows coupling suspended particles [21,22]. We report on experiments using spherical ion exchange resin particles sedimented to the negatively charged substrate.…”