Role of core-shell structure in binary mixture of amino sulfonate amphoteric surfactant with nonionic surfactant in solubilization behavior of pyrene

In order to understand the role of core-shell structure of mixed surfactant micelle and the effect of hydrophilicity of amphiphile in the enhanced remediation of contaminated soils and water, a novel amphoteric sodium 3-(N-dodecylethylenediamino)− 2-hydroxypropyl sulfonate (C12AS), three nonionic octylphenol polyoxyethylated ethers with unit number n of oxyethylene glycol ether (OP-n, n = 4, 7 and 10) and these binary mixtures of C12AS/OP-n were adopted to probe the solubilization behavior of pyrene by both the UV–vis spectrometric and the ¹H NMR techniques. Some parameters including the molar solubilization ratio (MSR), the partition coefficient (Pₘ), the standard free energy change (∆Gₚ) of partition, the interaction parameter (B) based on regular solution theory and the ratio (K₁/n) of first stepwise association coefficient (K₁) and aggregation number (n) in mixed micelle were estimated using different models. In these single surfactants, the values of MSR and Pₘ depend mainly on the hydrophilic-lipophilic balance (HLB) of amphiphiles for the homologues of OP surfactants. The solubilization behavior in these mixtures, however, does not again follow the HLB effect, but is subjected to the mixing ratio of component in mixed micelle and the micellar structure. The data from these B and K₁/n values can gain some understanding in tune with these parameters, e.g., MSR, Pₘ, R, etc. Based on the chemical shift of hydroxyl group, the core-shell structure of mixed micelle assumed in this investigation is proposed to demonstrate the solubilization locus and rationally describe the spontaneous process of solubilization and the related behaviors. These findings will help with understanding the solubilization behavior of hydrophobic organic compounds in these surfactants with a core-shell structure of micelle and designing the surfactant formulations in the surfactant enhanced remediation of contaminated soils and water.