球状胶束中表面活性剂脱附的离子调控机制

A coarse-grained molecular dynamics method coupled with umbrella sampling is developed to study the desorption process of SDS and CTAC surfactants from spherical micelles. The influence mechanisms of aggregation number, salt species and concentrations on the desorption process of surfactant from spherical micelles are revealed. We find that the radius and eccentricity of spherical micelles both increase with aggregation number rising, and the effects of salt concentration depend on the ionic radius and adsorption characteristics of the counterions. Larger salicylate ions with stronger adsorption ability have more significant effect on the micellar structures. Based on umbrella sampling method, we obtain the desorption free energy and time of surfactants from micelles. we find that the desorption free energy and desorption time of surfactant both show a non-monotonic variation with the increase of aggregation number and salt concentration, whose mechanisms are attributed to the electrostatic shielding induced by ion adsorption on micelle surface. Moreover, we reveal that the free energy plays a leading role in surfactant desorption process. Combing the theory of micelle thermodynamics, we further develop the critical micelle concentration prediction method, and obtain the distribution range of micelle size under the critical micelle concentration of surfactants.