Worm-like Micelle Formation of Sugar-Based Nonionic Surfactant with Multibranched Methyl Chains

The aggregation properties of sugar-based surfactants with methyl groups at multiple positions on the linear alkyl chain are an understudied topic. Therefore, in this study, we performed a structural analysis of aggregates formed by two types of sugar-based nonionic surfactants with multibranched methyl chains, 3,7,11-trimethyldodecyl maltoside (<i>b</i>C₁₅Mal), as well as with a linear chain, dodecyl-<i>β</i>-d-maltoside (C₁₂Mal), in aqueous solutions using rheological and small-angle X-ray scattering techniques. <i>b</i>C₁₅Mal showed an excellent performance in lowering surface tension (28.5 mN m^-1), exhibiting efficient adsorption and orientation at the air/water interface. <i>b</i>C₁₅Mal formed rod-like micelles at a concentration of 10 mmol dm^-3 in aqueous solutions and transitioned to worm-like micelles at 50 mmol dm^-3, followed by gel solutions at 700 mmol dm^-3. As the surfactant concentration increased, the length of the worm-like micelles decreased, and the mesh size decreased, indicating that the strings were densely packed. Conversely, C₁₂Mal formed ellipsoidal micelles over a wide range of concentrations from 50 to 700 mmol dm^-3. The major axis of the core and the overall axis of the ellipsoidal micelles decreased with increasing concentrations. Thus, it was clear that the introduction of methyl groups at positions 3, 7, and 11 of the dodecyl chain of the sugar-based surfactant resulted in a unique aggregation behavior, that is, the formation of aggregates with high-order structures at low concentrations.