Cloud point phenomena in aqueous solutions of an anionic gemini surfactant with a dibenzene spacer in the presence of tetra-n-propyl-ammonium bromide†
The cloud point (CP) behaviour of a carboxylate gemini surfactant, O,O′-bis(sodium 2-dodecylcarboxylate)-p-dibenzenediol (referred to as C12ϕ2C12), in aqueous solution has been examined in the presence of tetra-propyl-ammonium bromide (Pr4NBr), an organic salt with less hydrophobicity than that of commonly used species. The aggregates of C12ϕ2C12 in the solution were investigated by dynamic light scattering (DLS), steady-state fluorescence and rheological measurements. Compared with traditional single chain surfactants, C12ϕ2C12 showed the CP phenomena at very low surfactant concentrations. In the presence of Pr4NBr, C12ϕ2C12 in aqueous solution formed several types of aggregates with different sizes. As the temperature was raised to the CP, the micelles rapidly associated, resulting in a cloud-like appearance of the solution. The mechanism has been attributed to C12ϕ2C12, which can provide an attractive force for the micelle–micelle contact. Namely, with increasing temperature, some of the C12ϕ2C12 molecules within the micelles changed their configuration from cis- to trans-form, leading to some tails of C12ϕ2C12 in aggregates stretching towards the solution. When such micelles approached each other, these projecting tails interacted hydrophobically, and this resulted in the association of the micelles.