Mechanism Of Vesicle Structure Transform With Gemini Surfactants

Vesicle is composed of crust which forms from closed unimolecule-bilayer that combined with monolayers of two amphiphilic molecules in tail-to-tail orientationally, and micro-hydrofacies that is contained within the crust. It can be sort into two types: vesicle made up of natural or complex lecithin and vesicle made by self assembly of amphiphilic molecules. Cell membrane is made up of 40-50% lipoid and 50-60% protein. According to the model of liquid incrustation, bilayer of molecule composed by lecithin is the base frame work of cell membrane, where protein enchase to act as osmotic barriers. Every lecithin molecule of bilayer can move freely. As a result, the bilayer is moveable, flexile, high electric resisitant and resistant for high polarity molecule. So, the cell membrane has a dynamic and floating structure.Gemini surfactants are made up of two amphiphilic moieties covalently connected by a spacer group, and represent a new class of surfactants. According to lots of papers, the nature of the spacer group (length, flexibility, chemical structure) has been shown to be of the utmost importance in determining the solution properties of aqueous Gemini surfactants. So they are attracting considerable interest in the academic and industrial communities working onsurfactants. In this paper, we study a kind of Gemini surfactants------quaternary ammoniumGemini connected by the space chain of (CH₂)_s.The structural transitions induced by addition of the cation surfactants (quaternary ammonium Gemini surfactants) to small unilamellar lecithin vesicles have been studies by means of dynamic light scattering, transmission electron microscopy (TEM) and fluorescence. The mechanism is studied at the mean time.When the quaternary ammonium Gemini surfactants are added into the pure lecithin vesicle system without adding cholesterol, a combination of dynamic light-scattering and fluorescence probe techniques has been used to study the structure transform of lecithin vesicle with surfactants with different spacer chain length. The mechanism of structure transform of vesicle is explored by model and effective packing parameter theory. The results show that the main reason which leads the structure transform is the change of superficial electric charge of vesicle and the asymmetric distributing of the surfactant molecular in the vesicle. Further more, the structure of surfactant is also one of the reasons. Surfactants with different spacer chain length have different effects on changing the structure of the vesicle, which turn out to have some rules.Secondly, we studied the lecithin vesicle system with cholesterol. When the quaternary ammonium Gemini surfactants are added, the results turn out that the same concentration of the quaternary ammonium Gemini surfactants can not breach the vesicle. So we speculate that it is because the molecule of the lecithin and cholesterol can allure each other which induce the vesicle becomes too tight for the surfactants to embed.