Worm-like Micelle\nFormation of Sugar-Based Nonionic\nSurfactant with Multibranched Methyl Chains

The\naggregation properties of sugar-based surfactants with methyl\ngroups at multiple positions on the linear alkyl chain are an understudied\ntopic. Therefore, in this study, we performed a structural analysis\nof aggregates formed by two types of sugar-based nonionic surfactants\nwith multibranched methyl chains, 3,7,11-trimethyldodecyl maltoside\n(<i>b</i>C<sub>15</sub>Mal), as well as with a linear chain,\ndodecyl-<i>β</i>-d-maltoside (C<sub>12</sub>Mal), in aqueous solutions using rheological and small-angle X-ray\nscattering techniques. <i>b</i>C<sub>15</sub>Mal showed\nan excellent performance in lowering surface tension (28.5 mN m<sup>–1</sup>), exhibiting efficient adsorption and orientation\nat the air/water interface. <i>b</i>C<sub>15</sub>Mal formed\nrod-like micelles at a concentration of 10 mmol dm<sup>–3</sup> in aqueous solutions and transitioned to worm-like micelles at 50\nmmol dm<sup>–3</sup>, followed by gel solutions at 700 mmol\ndm<sup>–3</sup>. As the surfactant concentration increased,\nthe length of the worm-like micelles decreased, and the mesh size\ndecreased, indicating that the strings were densely packed. Conversely,\nC<sub>12</sub>Mal formed ellipsoidal micelles over a wide range of\nconcentrations from 50 to 700 mmol dm<sup>–3</sup>. The major\naxis of the core and the overall axis of the ellipsoidal micelles\ndecreased with increasing concentrations. Thus, it was clear that\nthe introduction of methyl groups at positions 3, 7, and 11 of the\ndodecyl chain of the sugar-based surfactant resulted in a unique aggregation\nbehavior, that is, the formation of aggregates with high-order structures\nat low concentrations.