FLOCCULATION OF STERICALLY STABILIZED POLYSTYRENE LATEX-PARTICLES BY ADSORBING AND NONADSORBING POLY(ACRYLIC ACID)

The stability of sterically stabilized polystyrene latex has been inve stigated in the presence of poly(acrylic acid) (PAA) at various pH val ues. Flocculation (aggregation) has been monitored by microscopy for a series of samples with various PAA concentrations at fixed latex volu me fraction and pH values. It was found that at low pH values (<4) bri dging flocculation occurred at a low critical flocculation concentrati on of PAA, but no restabilization was found, even when the PAA concent ration (weight fraction) reached 0.10. At pH >7, three different phase regions could be established on the phase diagram, namely, depletion flocculation at lower PAA concentrations (W(p)+ < W(p) < W(p)++ where W(p) is the weight fraction of PAA), depletion stabilization at higher PAA concentration (W(p)++ < W(p) < W(p)se) and a secondary unstable r egion (W(p) > W(p)se), where phase separation occurs, at very high PAA concentrations. The molecular weight has little influence on depletio n restabilization at higher pH. However, it influenced the critical br idging flocculation concentration (CBFC) and critical depletion floccu lation concentration (CDFC), i.e. the larger the PAA molecular weight the lower the critical flocculation concentration of polymer. Rheologi cal data showed the same CFC as the microscopy results at the secondar y unstable region. The effects of particle size, latex volume fraction , PAA molecular weight, and PAA concentration on viscoelastic properti es of the suspensions at pH = 8.0 and 9.0 were also studied.