MOLECULAR DYNAMICS STUDY OF SURFACTANTS ON A WATER SURFACE

Molecular dynamics simulations of three kinds of normal alcohols, n-propanol, n-heptanol and n-undecanol, on a water surface were carried out. In the case of n-propanol, when the concentration of n-propanol is low, n-propanol molecules are adsorbed on a water surface. As the concentration of n-propanol increases, water and n-propanol are well mixed. In the case of n-heptanol, the calculation results show that the steady states appear discretely, as the concentration of n-heptanol increases. When n-heptanol molecules don't exist, or the monolayer or polylayer of n-heptanol is formed on a water surface, the fluctuations of a water surface are small. But on the other concentrations large fluctuations can be observed. In the case of n-undecanol, n-undecanol and water are not mixed and the first adsorption layer of n-undecanol is always steady. The reason why interfacial turbulence occurs during water vapor absorption into an aqueous electrolyte solution with n-heptanol and such interfacial turbulence doesn't occur in the solution with n-propanol or n-undecanol seems to be related to the molecular dynamics of these alcohols on a water surface. During water vapor absorption, n-heptanol molecules move around on the surface to form local steady states.