Aggregation and Gelation in a Tunable Aqueous Colloid-Polymer Bridging System

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 polymer molecular weight, and normalized polymer concentration c/c^*. Bridging interactions were induced between trifluoromethyl methacrylate-co-tert-butyl methacrylate (TtMA) particles 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 c/c^* (pH ≈ 3.9) and the structure and extent of flocculation depends on the polymer size. Floc size is larger at higher molecular weight due to the larger polymer radius of gyration. By quantifying dynamics and structure, we show that the bridging suspensions transition from gel-like to fluid-like upon increasing c/c^*. These results provide insight into flocculation processes in applications such as wastewater treatment and creation of dense markers for indirect detection of diseases such as HIV and influenza.