Evaluation of surface, foam, emulsion, and clouding properties of a family of nonionic surfactants from oleic acid derivatives

This study investigated the properties, namely: surface tension, foam, emulsion, and cloud point of a library of bio-based surfactants (represented as C_nEO_m where C is hydrophobic carbon chain and EO is ethylene oxide). The surfactants were derived from ring-opening alkyl oleate epoxides with polyethylene glycol (PEG) and monomethyl polyethylene glycol (MPEG) of varying chain lengths. Surfactants demonstrated good surface properties having surface tension at critical micelle concentration (CMC) between 35 and 38 mN/m, and recorded CMC values far lower than what was reported for most commercial ethoxylated surfactants. Foamability increased with over 30% foam increase upon increasing agitation speed from 6000 to 11,000 rpm. Branching, hydrophobic carbon chain length, and PEG chain length were seen to impact foamability and foam stability. Foam properties exhibited by the surfactants were found to be superior to those demonstrated by some known commercial nonionic surfactants. Emulsions formed by the oleate ester surfactants were stable over several weeks after formation. Surfactants showed high cloud points, which increased with increasing number of ethylene oxide units. However, the addition of co-solutes depressed the cloud point in the order Na₂SO₄ > NaCl > NaNO₂.