Experimental study of the dynamics of hard and soft colloids during continuous microdroplet formation*

Owing to their design flexibility and high interfacial energies, colloidal particles are emerging as alternatives to surfactants as droplet stabilizer (Pickering emulsions)¹. It is well known that surfactants affect drop formation and sizes²; however, the effects of particles and their dynamics inside the droplets and at interfaces during emulsification remain largely unknown. In this work we investigate the dynamics of formation of colloid-stabilised droplets in a flow-focusing microchannel and study the effect of different particle attributes on drop sizes. Silicon oil was used as outer phase, while glycerol/water solutions containing fluorescent polystyrene particles (1 μm or 400 nm), or pNIPAM microgels of equal sizes, were used as droplet phase to study the effects of particle softness, size and concentrations. We used high-speed imaging to capture the dynamics of formation and μLIF to track particle distribution inside the droplets. A reduction of droplet size and formation time was observed with an increase in particle concentration and softness. In both scenarios, the adsorption kinetics are faster thus showing accordance with surfactant-based systems².

 

¹O.S. Deshmukh et al., Adv. Coll. Interf. Sci. 222, (2015).

²M. Kalli et al., J. Coll. Int. Sci. 605 (2022).