Electron density matching as a guide to surfactant design

Richard F. Tabor, Sarah Gold, Julian Eastoe

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25 Citations (Scopus)


The effectiveness at reducing interfacial tension between water and different organic solvents was studied, with 14 structurally different dichain sulfosuccinate surfactants. Variations in chemical structure ranged from linear/branched alkyl tail groups, to phenyl-tipped tail units, to partially and fully fluorinated tails. The solvents n-heptane, toluene, and perfluoroheptane were used as example oil phases. Interfacial activity was measured in terms of a reduced interfacial tension scale, RIFT, based on the value in the presence of surfactants compared to that for the pure solvent-water interface. Overall surfactant chain structure was determined to be the key factor affecting RIFT. Furthermore, a strong correlation was observed between R IFT and the electron density ρe of the different surfactants: with any given oil, the most effective surfactants have ρe values closest to that for the solvent. For example, phenyl-tipped surfactants were shown to be comparatively more effective at the interface with an aromatic solvent (toluene) than with an aliphatic n-alkane (heptane). Furthermore, fluorination of the tail groups decreased effectiveness at the hydrocarbon/water interface, which was substantially increased at the fluorocarbon/water interface: this too followed the electron density-matching pattern. The importance of chain-tip chemical structure was also noted, with regard to the introduction of phenyl, CF3-, and H-CF3- terminal moieties. For branched alkyl-tailed surfactants, it was found that effectiveness could be linked to an empirical "branching factor". The significance of the electron density matching of organic solvent and surfactant for the prediction of interfacial activities is highlighted, and this concept may prove useful for the future design of new high-efficiency surfactants.

Original languageEnglish
Pages (from-to)963-968
Number of pages6
Issue number3
Publication statusPublished - 31 Jan 2006

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