| Abstract
| - Simulations of mixed cationic/anionic wormlike micellar systems have been carried out for a wide range ofcompositions, including pure anionic and cationic systems. It was found that the wormlike micelle formed by onlycationic surfactant molecules is unstable and transforms to a set of small spherical micelles. Adding anionic surfactantswith a short hydrophobic chain (only eight carbon atoms) results in stable wormlike micelles. The 34/66 cationic/anionic worm is stable and symmetrical, while the 50/50 mixture yields a flattened worm, indicating a phase transitionto the lamellar phase. All these observations are in excellent agreement with the experimental results of Raghavanet al. (Langmuir2002, 18, 3797), and they provide a molecular mechanism for their observations. The addition ofoctyltrimethylammonium chloride increases the radius of the worm due to the bigger hydrophobic part. Meanwhile,the length of the worms decreases with the concentration of cationic surfactant and reaches a minimum for the 50/50mixture. The latter system is of special interest due to a zero surface charge density. The worm with the electrostaticallyneutral surface was used to investigate intermicellar interactions. The molecular dynamics (MD) simulations showthat the merging process requires a substantial activation energy even in the case of reduced electrostatic repulsion.
|
