Light Induced Particle Separation

• Applicant: Dr. Marek Bekir
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 469240574

The main goal of the project is to establish a light-driven separation mechanism for heterogenous micro-particle ensembles with respect of different surface modification (e.g. increasing roughness, porosity or covering with a thin polymer shell). Spatial separation is accomplished by simple irradiation with light. The physical principle is based on our previous experimental observations with using photosensitive, azo-containing surfactant with a cationic head group to generate light-driven diffusioosmosis (LDDO) at solid-liquid interfaces. Under irradiation the azobenzene photo-isomerizes from a more hydrophobic (trans-isomer) to a more hydrophilic state (cis-isomer); the conformational difference thus decides to which extent an isomer can be accommodated by the particles or be released back into bulk solution. The interplay of trans-isomer adsorption and cis-isomer desorption generates a local form of light driven diffusioosmotic (l-LDDO) flow, which is stronger for particles capable of storing large amounts of surfactant, determined by e.g. pronounced roughness or porosity, for instance, conveyed by a suitable polymer coating acting as an absorber. This characteristic translates into a higher velocity when subjected to an external hydrodynamic flow. The superimposed l-LDDO flow field generates a large slip-velocity, and the extent of separation is simply determined by the elution time when the particle ensemble is subjected to external flow. Devising a simple and swift method for separating heterogenous colloidal particles distinguished only by slight differences in their surface morphology, given equal size and material composition would be highly desirable, for instance, as a purification method.

• DFG Programme: Research Grants