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 nanoand 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.