Micellar properties of non-ionic surfactants in relation to their solubility parameters

Abstract

The solubility parameters of various polyoxyethylated non-ionic surfactants were calculated according to 3 different methods: by Fedors approach; from molar attraction constants; by including a hydrogen-bonding component to account for hydration. The computed solubility parameters for the surfactants were then correlated with their critical micelle concentrations (CMC). The relationships included 3 homologous surfactant series based on polyoxyethylated ethers, octyl- and nonyl-phenols, and fatty acid esters of sorbitan. The total solubility parameters, δ 0, corrected for hydrogen bonding increased linearly with increasing the CMC. The resulting linear relationships permit the prediction of the CMC of any surfactant within a homologous series from any of its calculated solubility parameters. Branching of decaoxyethylated octylphenol to give t-octylphenol decreased the CMC by a factor of 1.3, and increased δ 0 by 0.31 (cal/ml) 1 2 . The presence of double bond in TWEEN 80 decreased the CMC by a factor of 2, and increased δ 0 by only 0.03 (cal/ml) 1 2 . A greater double bond effect on solubility parameter of ~1.0 (cal/ml) 1 2 was noticed in the case of long-chain polyoxyethylated ethers than in TWEENs. The double bond contribution to CMC and to the total solubility parameter is not additive for the different homologous series and varies with the surfactant structure. The solubility parameter concept was also applied to analyse some solubilization data.