Controlled fabrication of polymer microgels by polymer-analogous gelation in droplet microfluidics
"Controlled fabrication of polymer microgels by polymer-analogous gelation in droplet microfluidics" Sebastian Seiffert and David A. Weitz. Soft Matter 6, 3184-3190 (2010).
This paper discusses the fabrication of polymer microgels using droplet microfluidic devices. An aqueous, semi-dilute solution of pNIPAAm (N-isopropylacrylamide) is flowed through a central channel in PDMS (poly-dimethyl siloxane) microfluidic device. This channel reaches a junction where two oil-carrying channels merge, one from each side, pinching off the pNIPAAm into small droplets, as seen in figure 1. The droplets are flowed downstream through ultraviolet light where the pNIPAAm solidifies. The solidification happens through a photochemical pathway where UV light induces crosslinking between pNIPAAm chains. The droplet size is controlled over a wide range by adjusting the flow rate and dilution of pNIPAAm. The pNIPAAm dilution consists of chains with molecular weights of 200,000g/mol and a 0.75% concentration of DMMI. The DMMI forms the crosslinks.
This method allows for varying degrees of microgel cross-linking by controlling the strength and duration of the UV light. At the higher end, it leads to gels with higher crosslinking efficiency and greater homogeneity than traditional free-radical crosslinking techniques. It also allows for the fabrication of new microgels for sensing and actuation applications.