Focusing Diffusiophoresis and Oil Droplet Solvophoresis Studies with Integrated Hydrogel Membrane Microwindow

The phenomena that colloids could migrate via diffusiophoresis in response to concentration gradient provide intriguing methods to transport particles in solution. However, this potential is often underestimated largely due to the ambiguous understanding that the migration always follows up the concentration gradient. Recently, we have developed a microfluidic system that enables us to create stable and high solute and solvent gradient across the microchannel and therefore quantitatively measure the colloids velocity. Here, we present experiments performed in this microfluidic system and demonstrate, for the first time, that colloidal migration under diffusiophoresis can exhibit opposite directions simultaneously in a multi-component solution. Moreover, we perform solvophoresis in this microfluidic system with oil droplets that allows inward flux. Based on the partition coefficients of applied solvent in water-oil system, these oil droplets react to the concentration gradient in a different ways from solid polystyrene beads. These observations open the door to novel manipulation of soft matt colloids.