Long-time relaxation of suspensions flocculated by associating polymers

Associating polymers are hydrophilic long-chain molecules containing a small amount of hydrophobic groups and act as flocculants in colloidal suspensions. The rheological properties of suspensions flocculated by associating polymers end-capped with hydrophobic groups are studied in relation to the bridging conformation, The flow of flocculated suspensions is Newtonian at very low shear rates. The liquidlike responses in the limit of zero shear rates imply that the polymer bridges are constantly forming, breaking, and reforming in a quiescent state, Due to the weak affinity of polymer for the particle surface, the adsorption-desorption process reversibly takes place by thermal energy. At low polymer concentrations, the polymer chains effectively form bridges between particles. From the high storage modulus and short surface separation between particles, it is considered that one polymer chain is directly adsorbed onto two particles to bind them together, because the hydrophobic groups are incorporated on the ends. With increasing polymer concentration, the relaxation time decreases and surface separation increases. The suspensions with polymer at relatively high concentrations are highly elastic even under large strains in the nonlinear region. The particles may be connected by bridges of interchain associations that are soft and flexible. The main factor controlling the rheology of suspensions is the bridging conformation, which varies strongly depending on the particle and polymer concentrations.