Structural study on aggregation behavior of star-type trimeric surfactant in the presence of sodium salicylate

本論文の著作権はElsevier B.V.社が保有している。著者最終稿については、出版後24カ月経過した2018年5月20日に公開される。
•3C_12trisQ aggregates in NaSal solution were studied by SAXS and rheological measurements. •3C_12trisQ aggregates evolved from wormlike micelles to MLVs with increasing the C_S. •The structural transitions of the 3C_12trisQ aggregates strongly depended on both C_S and C_D. -------------------------------------------------We investigated the aggregation behavior of star-type trimeric surfactants (3C_12trisQ) with a hydrocarbon chain length (n) of 12 in sodium salicylate (NaSal) aqueous solution at various surfactant (C_D) and salt concentrations (C_S) using small-angle X-ray scattering (SAXS) and rheological measurements. At a low surfactant concentration (C_D = 7 mM), 3C_12trisQ aggregates in solution evolved from ellipsoidal micelles, to rodlike or wormlike micelles and finally to multi-lamellar vesicles (MLVs) with increasing C_S. In contrast, at higher surfactant concentrations (C_D = 14 and 28 mM), we did not observe vesicle formations of 3C_12trisQ because 3C_12trisQ were insoluble in solution at higher NaSal concentrations. The structural transitions of the 3_C12trisQ aggregates strongly depended on both CS and CD. We also compared the MLV structure formed by 3C_12trisQ with that formed by gemini-type surfactants (12-2-12). The repeat distance of the 3C_12trisQ MLV (33.95 Å) was remarkably larger than that of the 12-2-12 (22.36 Å). We found that introducing spacer chains, i.e., from dimeric to trimeric surfactants, caused a decrease in NaSal concentrations at which micelle-to-vesicle transitions were observed.