Latex Thermostimulated Flocculation in Poly(N-Vinylcaprolactam) Solutions

The effect of temperature on the flocculation of dilute polystyrene latex in the presence of poly(N-vinylcaprolactam) (PVC), a thermosensitive polymer interacting with water to form systems characterized by a lower critical mixing temperature, is studied by the nephelometry. It is shown that PVC induces latex flocculation only in the presence of a small amount of an inorganic electrolyte. Dependence of the initial flocculation rate on PVC concentration has an extremal pattern, which is typical of polymer flocculants. At concentrations close to those of optimal flocculation, heating in the range below the phase separation temperature (T_ps) increases the flocculation rate and the sizes of forming aggregates. It is found that, at PVC concentrations that do not induce the flocculation at room temperature, heating in the range above T_ps (in the presence of a sensitizing electrolyte) results in an irreversible latex flocculation. The disclosed thermostimulated flocculation is assumed to be due to the deterioration of the solvent thermodynamic quality.