Monolayers of Mixed Surfactants at the Oil-Water Interface, Hydrophobic Interactions, and Stability of Water-in-Oil Emulsions (original) (raw)

The present study involves investigation of monolayer properties of sorbitan monooleate and diethanolamine derivatives of polyisobutylene succinic anhydride of three different molecular weights, viz. 500,700, and 1050, as single as well as binary mixtures at the oil-water interface. The average backbone carbon numbers of the polyisobutylene chains are 14,22, and 34, respectively. The monolayer studies at the oil-water interface were carried out with a specially designed Langmuir trough. The investigations were carried out at two different oil phases, viz. heptane and paraffin oil. The packing efficiency of these surfactants (single or in combination) are found to be greatly influenced by the oil chain length. Within the limits of experimental accuracy, the mixed surfactant systems comprising sorbitan monooleate and polyisobutylene surfactants of three different hydrocarbon chain lengths follow the rule of hydrocarbon chain length compatibility. The observed differences in packing features revealed the significance of oil penetration and cohesive interactions in the aliphatic layer of the surfactant film. The efficacy of these surfactants were further examined in water-in-oil emulsions and the results are consistent with the findings of monolayer properties. At the condition of chain length compatibility, the mixed surfactant system produced emulsions with maximum stability.