Droplet Microfluidics for Fabrication of Non-Spherical Particles
Original entry by Caspar Floryan, APPHY 225 Fall 2010
"Droplet Microfluidics for Fabrication of Non-Spherical Particles" Ho Cheung Shum, Adam R. Abate, Daeyeon Lee, Andre´ R. Studart, Baoguo Wang, Chia-Hung Chen, Julian Thiele, Rhutesh K. Shah, Amber Krummel, David A. Weitz, Macromolecular Rapid Communications. 31, 108-118 (2010).
Particles, Colloids, Non-spherical, Droplet, Microfluidics
This paper discusses the production of non-spherical particles using droplet microfluidics. Small colloidal particles tend towards a spherical shape as a result of surface tension, which dominates over all other forces at this size scale. Single and multiple emulsion droplets are transformed into non-spherical particles using several methods, including (1) arrested coalescence, (2) asymmetric polymer solidification, (3) polymerization in microfluidic flow, and (4) evaporation-driven clustering.
Non-spherical particles could have important applications in cosmetics, biotechnology, structural materials and pharmaceuticals as the non-spherical shape offers properties not available in traditional, spherical particles. Non-spherical particles can pack more densely and can also behave differently in electric, magnetic and hydrodynamic fields.
Arrested Coalescence This technique involves initiating droplets to coalescence and freeze their shape before they relax into spheres. The droplet’s surface is partly coated with Pickering particles, tiny spherical particles, leaving open patches. These openings initiate droplet coalescence before it has relaxed into a sphere.
Asymmetric Polymer Solidification This method takes advantage of non-isotropic solvent evaporation. The droplet is immersed in a volatile solvent which is manipulated using microfluidics to evaporate non-isotropically. This results in torroidal particles.
Polymerization in Microfluidic Flow A double emulsion particle (a droplet inside a droplet) is created inside a microfluidic device such that the particle’s diameter is larger than the channel’s. The particle becomes stretched and this non-spherical shape is locked-in by polymerization.
Evaporation-Driven Clustering This technique involves the creation of multiple emulsions with several droplets inside a larger droplet. The inner droplets push on the surface of the outside droplet, morphing it into a non-spherical shape. The outer droplet is coated with small colloids. The droplets are evaporated, leaving a non-spherical colloidosome (a particle made of many colloids).