Revisiting the influence of carboxylic acids on emulsions and equilibrated SOW systems using the PIT-slope method

Abstract

The influence of various carboxylic acids (from C2 to C18) one equilibrated and emulsified surfactant/oil/water (SOW) systems is investigated. The PIT-slope method, based on the influence of an additive on the PIT of the C10E4/n-octane/10−2M NaCl(aq) reference emulsion, shows that from butanoic to hexadecanoic acids, the PIT of the system is decreased. A breakdown on dPIT/dx (considering the molar fraction x) or a minimum on dPIT/dC (taking into account the weight percentage C) is obtained with octanoic acid. The phase behavior of the C10E4/carboxylic acid/n-octane/0.01M NaCl(aq) system maintaining a molar fraction of carboxylic acid xCA=0.2 shows that from octanoic acid, the solubility of the system is clearly enhanced explaining the breakdown obtained in the PIT-slope. The Span 80/carboxylic acid/oil/10−2M NaCl(aq) system at a water-to-oil ratio equal to 1 is able to form O/W emulsions in the presence of some carboxylic acids, of which the alkyl chain modifies the partition of the different oligomers of Span 80. Finally, the PIT-slope method is applied to mixtures of lauric acid/sodium laurate providing a linear behavior of the PIT-slope dPIT/dx as a function of the acid/salt ratio.