Solubilization of styrene in the catanionic system dodecyltrimethylammonium hydroxide–n′-dodecanephosphonic acid

 The solubilization of styrene in micelles of the catanionic surfactant dodecyltrimethylammonium hydroxide (DTAOH)–n-dodecane-phosphonic acid (DPA) was studied by UV–Vis. spectrometry, as a function of the DTAOH:DPA proportion in the surfactant mixture. The styrene molecules are adsorbed at the surface of the micelles, with the vinyl group closer to the hydrocarbon core than the aromatic ring, which is oriented to the water. In micelles with an excess of DTAOH, the dielectric constant of the water surrounding the micelles was strongly affected by the non-neutralized –N(CH₃)⁺ ₃ groups at the Stem layer. In micelles with an excess of DPA, the –PO₃H₂ groups which are not neutralized by –N(CH₃)⁺ ₃, remain almost unionized and hydrogen-bonded. The effect of the micellar surface on the surrounding water dielectric constant dropped sharply. The dielectric constant in the hydrogen-bonded polar layer is ∼65, rising to the value of pure water very close to the micellar surface. Received: 2 September 1997 Accepted: 20 October 1997