Salt Effect on Polymerizable Vesicles of Allyl Dodecyl Dimethylammonium Bromide and Sodium Dodecyl Sulfonate in Aqueous Solution

Abstract

AbstractPolymerization reactions in vesicles are known to fix the vesicular structure to provide stabilized hollow colloidal nanoparticles used as biological membrane models, drug delivery vehicles, or templates for the synthesis of nanostructures. As a precursive work of polymerization directly from vesicles, a polymerizable surfactant, allyl dodecyl dimethylammonium bromide (ADDB) was synthesized, and spontaneous stable vesicles were formed from aqueous solutions of ADDB and sodium dodecyl sulfonate (SDS) in equimolar composition. The aqueous mixture of ADDB/SDS could form homogeneous solutions even at a high surfactant or sodium bromide (NaBr) concentration. Before polymerization, salt effect on the polymerizable vesicles was investigated by using dynamic light scattering (DLS) and freeze‐fracture transmission electron microscopy (FF‐TEM) measurements. It was interestingly revealed by the DLS method that the vesicle size increased from 83 nm in a salt‐free solution to 250 nm with increasing the salt concentration to 250 mmol/L, but decreased from 250 to 180 nm with increasing the salt concentration to 1000 mmol/L. The same meaningful trend was disclosed by the FF‐TEM measurements that when NaBr concentration was below 150 mmol/L the dispersed individual vesicle size was about 70 nm but it decreased to 20 nm while the NaBr concentration was above 400 mmol/L. The causation of increment of average aggregate radius can be attributed to the fusion and flocculation of vesicles observed clearly under a TEM imagine. The decrease of vesicle size results from the fact that, at a high salt concentration, electrolyte screens the interaction between the charged head groups, thus entropic increase drives big vesicles to decrease to small ones.