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 a combination of pressure‐driven microfluidic flow and local self‐phoresis/osmosis are proposed via the light‐induced chemical activity of a photoactive azobenzene‐surfactant solution. This process induces a vertical displacement of the sedimented particles, which depends on their size and surface properties . Consequently, different colloidal components experience different regions of the ambient microfluidic shear flow. Accordingly, a simple, versatile method for the separation of such 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 the separation of bulk‐porous from bulk‐compact colloidal particles and the separation of particles distinguished solely by slight differences in their surface physico‐chemical properties. A versatile method for separating colloids distinguished only by slight differences in their surface morphology (e.g., roughness, porosity, or polymer), is reported. It relies on combining the drift by the pressure‐driven shear flow of a photosensitive surfactant solution with a surface‐properties‐dependent positioning of the particles within the shear flow via local active flows induced under suitable illumination.