Molecular dynamics study on the aggregation behaviours of Platonic micelle in different NaCl solutions

Abstract

Calixarene-based amphiphiles are new types of monomers to form self-assemblies with profound applications. Micelles formed by these amphiphiles are classified as Platonic micelles. The effects of different NaCl concentrations of 10, 15 and 100 mM on sulfonated amphiphilic calix[4]arene (SC4AP) micelles are studied by all-atom molecular dynamics (MD) simulation. Structural characteristics including micelle shape and size, solvent accessible surface area, radial distribution function, hydration number, the adsorption of sodium (Na+) ion on micelles and micellar configuration, are analyzed at the molecular level. The MD results show that all micelles are not perfectly spherical. With the increase of NaCl concentration, more Na+ ions are absorbed on micelle surface. However, the increasing extent of adsorbed Na+ ions decreases at large NaCl concentration. Two adsorption modes of Na+ ions on micelles are found. One attracting point is that each cavity of SC4AP molecule include one adsorbed Na+ ion with one hydrated water molecule. Representative configurations of tetramer and hexamer SC4AP micelles under different NaCl concentrations are proposed. At 10 mM NaCl concentration, tetramer SC4AP micelles switch between tetrahedron and planar quadrilateral structures during simulations.