Spontaneous crystallization at the air-water interface: An unusual feature of gemini surfactant with a rigid Spacer

An unusual feature which involves spontaneous crystallization at the air-water interface from aqueous solution was reported for a water-soluble gemini surfactant with xy1y1 spacer, (p-phenylenedimethylene) bis(dodecyldimethylammonium) dibromide. Polarizing microscope, in situ confocal microscopic Raman spectroscopy, and powder XRD were used to characterize the structure of the crystal and investigate the driving force for nucleation. It was inferred that, besides the surface enrichment of amphiphiles and the intra- and intermolecular interaction of alkyl chains, the pi-pi stacking interaction of benzene rings plays an extraordinary role in promoting nucleation and stabilizing crystal structure. A mechanism for constructing supramolecular architectures in situ at the air-water interface directly from aqueous solution via water-soluble amphiphiles with groups favorable for d-d stacking interaction was proposed.