Formation Kinetics of Polymer Vesicles from Spherical and Cylindrical Micelles Bearing the Polyelectrolyte Complex Core Studied by Time-Resolved USAXS and SAXS
| Autor: | Rintaro Takahashi, Theyencheri Narayanan, Shin-ichi Yusa, Takahiro Sato |
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| Rok vydání: | 2022 |
| Předmět: | |
| Zdroj: | Macromolecules. 55:684-695 |
| ISSN: | 1520-5835 0024-9297 |
| Popis: | Polymer vesicles (polymersomes) have received considerable attention in the last several decades, but little has been known about the kinetics of the formation process, despite their importance both scientifically and in practical applications. Here, we reported the formation kinetics of polymer vesicles in aqueous NaCl solutions of anionic–neutral and cationic–neutral block copolymers when they transform from micelles with a polyelectrolyte complex core. Vesicle formation from spherical or cylindrical micelles was initiated by fast mixing with a stopped-flow device. We then employed time-resolved ultrasmall-angle X-ray scattering with millisecond resolution, which enabled monitoring the kinetic process of vesicle formation. An in-depth analysis of the scattering data elucidated the following processes: in the case that the initial state was spherical micelles, they grew with time to form short cylindrical micelles. These short cylindrical micelles then transformed into disklike micelles, which subsequently closed to form vesicles. On the other hand, when the initial state involved cylindrical micelles, the disklike micelles similarly assembled, which then transformed into vesicles. The bilayer membrane of vesicles used in this study was 4 times thicker than that of vesicles formed from conventional low-molecular-weight surfactants; hence, the bending rigidity of the bilayer was approximately 16 times higher. Due to this feature, the kinetic process was different from that of conventional low-molecular-weight surfactants, in particular, an increase in the size of the disklike micelles was not observed. Instead, the weight fraction of the disklike micelles gradually decreased, and concomitantly, the weight fraction of vesicles increased since the larger transient disklike micelles or bowl-like micelles were unstable. This behavior could be well reproduced by our proposed kinetic model. This is the first report on the self-assembly kinetics of polymer vesicles probed by time-resolved small-angle scattering. |
| Databáze: | OpenAIRE |
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