Solid Surface-Mediated Aggregation Structural Transformation Of Lauryl Sulfobetaine And Amphiphilic Block Copolymer Pluronic P123

Vesicles, one of the amphiphilic molecule organized assemblies constructed by unilamellar or multilamelar closed bilayers, have attracted much interest over the past several decades because of their fundamental and practical importance. Broad application prospects of vesicles have been revealed, as models for cell membranes, vehicles for encapsulated and controlled delivery of drugs, microreactors, templates for the synthesis of nanoparticles. A large number of vesicles in aqueous solutions of surfactants and amphiphilic polymers have been reported. As far as we know, the studies on the conventional simple single-tailed surfactant (STS) spontaneous formation of vesicles were rarely reported. A simple STS is usually considered to be unable to form vesicles in water in the absence of cosurfactants or additives. However, we recently found that the cationic surfactant DTAB could form vesicles from its micellar solution with the mediation of a rough glass surface (RGS) in the absence of cosurfactants and additives. Importantly, the obtained DTAB vesicles displayed good stability. This seems to be contrary to exsiting theory, causing our interest. In addition, it has been reported that vesicles can be prepared by many methods, such as change the pH, temperature and salinity, and via the addition of organic additives. But the method of solid surface-mediated formation of vesicle from solution has not been trported.In this paper, we adopted zwitterionic surfactant lauryl sulfobetaine (LSB) and block copolymer Pluronic P123 as models of amphiphilic molecules. And we adopted hydrophilic rough glass surface (RGS) and lipophilic glass surface (LGS) as models of solid surface. The paper studied solid surface-mediated transformation of aggregation from solution. And we explored the stability of vesicles and discussed the mechanism for aggregation structural transformation. This study aims to improve the understanding of interfacial phenomenon and the aggregation behavior of amphiphilic molecules.Main contents and conclusions:(1) We studied hydrophilic rough glass surface (RGS was obtained by etching a plate glass surface using HF) mediated aggregation structural transformation behavior from LSB micellar solutions. The LSB vesicles spontaneously formed from the solutions. The obtained LSB vesicles show good stability upon long-term storage, exposure to high temperature (80℃,2 h) and freeze-thawing (-20 or-196℃ for 2 h to approximately 25℃). The pH (4.0-9.0) of the LSB solution and the presence of NaCl (1.0 × 10-5 and 1.0× 10-4 mol/L) in the LSB solution have no obvious influence on the formation and stability of the vesicles. LSB can adsorb on the RGS to form bilayers, and the bilayer adsorption and the roughness of the solid surface played an important role in vesicle formation. A possible mechanism for the RGS-mediated formation of the LSB vesicles was proposed. The LSB micelles and molecules are adsorbed on the RGS to form curved bilayers, the curved bilayers subsequently detach from the RGS, and then close to form vesicles. The translation from micelles to vesicles for STSs in water without any additive poses a high free-energy barrier, and the mediation of RGS can overcome this barrier and then causes the translation occurred.(2) We studied lipophilic glass surface (LGS was obtained by modifing a plate glass surface by chlorotrimethylsilane) mediated aggregation structural transformation behavior from LSB micellar solutions. The formation of LSB vesicles was observed without any additives. The obtained LSB vesicles show good stability, the pH (4.0-9.0) of the LSB solution has no obvious influence on the formation and stability of the vesicles. These resurts are consistent with RGS-medicated formation of LSB vesicles. The possible mechanism for the LGS-mediated formation of the LSB vesicles was:the LSB micelles or molecules adsorb on the LGS to form a monolayer, the adsorbed monolayer further has an matrix effect (or enrichment effect) for free micelles, resulting in formation of bicelle-stacking aggregates on its surface; the bicelle-stacking aggregates were detached from the surface to form dispersed bicelles, and finally the bicelles close or coalesce to form vesicles. Hydrophilic glass surface-mediated formation of vesicles from P123 micellar solutions(3) We studied hydrophilic RGS mediated aggregation structural transformation behavior from P123 micellar solutions. The aggregation structure transformed from spherical micelles to worm-like micelles then to vesicles. The P123 vesicles were partly transformed into worm-like micelles after removing RGS. The obtained P123 vesicles transformed into worm-like micelles and spherical micelles upon long-term storage, exposure to high temperature (40～90℃) and freeze-thawing (-20 to 25℃). P123 spherical micelles can adsorb and aggregated on the RGS played an important role in transformation of aggregations.