Controlled fabrication of polymer microgels by polymer-analogous gelation in droplet microfluidics

We fabricate thermo-responsive polymer microgels by combining microfluidic pre-gel emulsification with polymer-analogous gelation. This separates the microgel formation from the polymer synthesis; it combines highly controlled microfluidic templating with the great flexibility of preparative polymer chemistry, allowing each to be controlled independently. We produce monodisperse pre-gel droplets from semidilute solutions of photocrosslinkable poly(N-isopropylacrylamide) precursors. The size and morphology of these droplets can be precisely controlled by the microfluidic emulsification, provided the molecular weight of the precursor is limited. Using polymer-analogous gelation rather than monomer chain-growth gelation yields gels with a higher efficiency of crosslinking and a greater homogeneity on nano- and micrometre scales, as determined by oscillatory shear rheology, static light scattering, and optical microscopy. We also demonstrate the applicability of our method to fabricate microgel particles with well-defined concentrations of functional sites.