Phase Behavior of Colloids with Attractive Polymer-Mediated Interactions

Attractive bridging interactions driven by polymers that adsorb to the particle surface are prevalent in separation processes. How the phase behavior, structure, and dynamics of the suspension depend on the strength of bridging interactions remains incompletely understood. We investigate the phase behavior of a colloid-polymer mixture with attractive bridging interactions in which the strength of the polymer adsorption can be tuned through the pH of the solution. Bridging interactions were induced between trifluoromethyl methacrylate-co-tert-butyl methacrylate (TtMA) by introducing poly(acrylic acid) (PAA) to the system. The formation of hydrogen bonds between PAA and stabilizers on the surface of the particles decreases as pH is increased. We find that the particles form flocs and networks at low pH but largely remain dispersed at high pH. By quantifying the dynamics and structure, we show that suspensions of TtMA particles and PAA undergo fluid to gel transition by decreasing pH or increasing polymer concentration at both low (φ = 0.15) and high (φ = 0.40) particle volume fractions.