Versatile Microfluidics Separation of Colloids by Combining External Flow with Light-induced Chemical Activity.

Separation of particles by size, morphology, or material identity is of paramount importance in fields such as filtration or bioanalytics. Up to now separation of particles distinguished solely by surface properties or bulk/surface morphology remains a very challenging process. Here we propose a combination of pressure driven microfluidic flow and local self-phoresis/osmosis via light-induced chemical activity of a photoactive azobenzene-surfactant solution. This process induces a vertical displacement of the sedimented particles and depends on the size and surface properties of the particle, thus, consequently, different particles experience different regions of the ambient microfluidic shear flow. Accordingly, simple, versatile method for separation of colloids can be achieved by elution times in a sense of particle chromatography. The concepts are illustrated via experimental studies, complemented by theoretical analysis, which include separation of bulk-porous from bulk-compact particles and separation of particles distinguished solely by slight differences in their surface physico-chemical properties. This article is protected by copyright. All rights reserved.