Low hydrophobically modified poly(acrylic acid) stabilizing macroemulsions: Relationship between copolymer structure and emulsions properties

Low hydrophobically modified (with dodecylamide chain) linear poly(acrylic acid) sodium salts (LHMPAANa) of various degrees of grafting (tau) and molecular weights were synthesized and used as emulsifiers of the n-dodecane/water (NaNO3 10(-3) M) system. Stability and how properties of the resulting n-dodecane in water emulsions (dispersed phase volume fraction = 0.5) were investigated as a function of tau (tau = 0 to 10% in mel), molecular weight (5000, 50,000, and 150,000 g/mol) and polymer concentration (0 to 10%). It was clearly shown that viscosification (via an associating mechanism of LHMPAANa) of the external phase of emulsions is a key factor in explaining dispersion breakdown. However, a complete description of the phenomenon could not be achieved without considering the adsorption of the polymer at the liquid-liquid interface which depends closely on tau but not much on molecular weight. The molecular weight effects were found to be restricted to the viscosification of the outer phase. (C) 1998 Academic Press.