Enhanced Stabilization of Vesicles by Compressed CO₂

In this work, we studied the effect of compressed CO₂ on the stability of vesicles formed in a dodecyltrimethylammonium bromide (DTAB)/sodium dodecyl sulfate (SDS) mixed surfactant system by combination of phase behavior and turbidity study, and UV−vis and fluorescence techniques. It was discovered that compressed CO₂ could enhance the stability of vesicles significantly. This new and effective method to stabilize vesicles has some unique advantages over conventional methods. For example, the size and stability of the vesicles can be easily controlled by CO₂ pressure; the method is greener because CO₂ is a green reagent and it can be released completely after depressurization, which simplifies postseparation processes in applications. The main reason for CO₂ to stabilize the vesicles is that CO₂ molecules can insert into the hydrophobic bilayer region to enhance the rigidity of the vesicle film and reduce the size of the vesicles, which is different from that of conventional cosolvents (e.g., alcohols) used to stabilize vesicles. On the basis of this discovery, we developed a method to prepare hollow silica spheres using tetraethoxysilane as the precursor and CO₂-stabilized vesicles as the template, in which CO₂ acts as both the stabilizer of the vesicular template and the catalyst for the hydrolysis reaction of the precursor, and other cosolvents and catalysts are not required. Besides, the size of the silica hollow spheres prepared can be controlled by the pressure of CO₂.