Stimuli-sensitive microgels are cross-linked polymeric particles that swell or shrink reversibly by absorbing or releasing solvent in response to changes in the surrounding temperature, pH, ionic strength, or electromagnetic field. Their responsiveness to the external environment makes them attractive candidates for applications in drug delivery, catalysis, sensing, and photonics. Poly(N-isopropylacrylamide), PNIPAM, microgels are an example of thermosensitive microgels: their size change is triggered by changes in temperature. The polymer chains forming these microgels contain both hydrophilic amide groups and hydrophobic isopropyl groups. When dispersed in water at low temperatures, generally below 32 °C, the hydrophilic interactions dominates and these interactions force water into the microgels causing them to swell. However, at higher temperatures, the hydrophobic interactions dominate and these interactions expel water out of the microgels and cause the particles to shrink dramatically.

This talk will describe the synthesis and characterization of novel supra-particles and structures formed through the directed assembly of colloidal PNIPAM microgels in droplets. The thermosensitive behavior of the microgels is effectively put to use in conjunction with surface functionalization to create these structures. We employ microfluidic techniques to create emulsions of aqueous microgel suspensions in oil. The use of these techniques allows the formation of monodisperse droplets and, thus, monodisperse self-assembled particles. I will also demonstrate how such designer particles can be useful as rheological probes, particle surfactants, micro-valves, and bio-vehicles for encapsulating and delivering macromolecules in pharmaceutical and cosmetics formulations.