Direct Observation of Phase Transition Dynamics in Suspensions of Soft Colloidal Hydrogel Particles

Abstract

Due to the tunability of their softness and volume as a function of temperature, poly(N‐isopropylacrylamide) (pNIPAm) hydrogel particles have emerged as a model system for soft colloidal spheres. By introducing AAc as comonomer, one can also tune the particle volume via pH. We report on the phase behavior of these stimuli‐responsive colloids as measured with a microdialysis cell. This device, which integrates microfluidics with Particle Tracking Video‐microscopy allows for simple and quick investigation of the phase behavior of suspensions the soft colloidal hydrogel as a function of pH as well as its packing density. In particular, we demonstrate the existence of an unusually broad liquid/crystal coexistence region as a function of effective particle volume fraction. Additionally, we reveal that nonequilibrium jammed states can be created in the coexistence region upon sudden large changes of pH. The phase diagram is indicative of complex interparticle interactions with weakly attractive components.