Journal
PHYSICAL REVIEW LETTERS
Volume 117, Issue 25, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.117.258001
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Funding
- Saudi Aramco under ASC [600013692]
- NSF [CBET-1438779]
- ADD [14-70-06-10]
- University of California, Santa Barbara
- University of California, Office of the President
- NSF MRSEC Program [DMR 1121053]
- NSF
- Directorate For Engineering [1438779] Funding Source: National Science Foundation
- Div Of Chem, Bioeng, Env, & Transp Sys [1438779] Funding Source: National Science Foundation
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Using a microfluidic system to impose and maintain controlled, steady-state multicomponent pH and electrolyte gradients, we present systems where the diffusiophoretic migration of suspended colloids leads them to focus at a particular position, even in steady-state gradients. We show that naively superpositing effects of each gradient may seem conceptually and qualitatively reasonable, yet is invalid due to the coupled transport of these multicomponent electrolytes. In fact, reformulating the classic theories in terms of the flux of each species (rather than local gradients) reveals rather stringent conditions that are necessary for diffusiophoretic focusing in steady gradients. Either particle surface properties must change as a function of local composition in solution (akin to isoelectric focusing in electrophoresis), or chemical reactions must occur between electrolyte species, for such focusing to be possible. The generality of these findings provides a conceptual picture for understanding, predicting, or designing diffusiophoretic systems.
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