The Aggregation Behavior Of Different Types Of Surfactant Interface

We performed all atom molecular dynamics simulation to study of the aggregate behavior of surfactants at the gaseous-liquid and liquid-liquid interface and discussed the dynamic properties of these systems from microscopic scale, and obtained some creative results. These studies are used to understand, explain and predict some results and phenomena of experiments and provide approaches of theoretical directive for further study of these systems.1. The aggregate behavior of AOT molecule at the isooctane/water interfaceIsooctane was chose as oil phase for having the similar structure with hydrophobic chains of the AOT (Aerosol OT, 2-ethylhexylsulfosuccinate sodium). First, the interfacial tension values of isooctane/AOT/water were measured on the experiment, and then investigated the configuration of AOT at the isooctane/water interface by molecular dynamics simulation. The effects of the kind of inorganic salt to interfacial configuration and aggregate behaviors were studied and discussed from experiment and simulation. The simulation results showed that AOT could form monolayer at the isooctane/water interface. Due to the electrostatic interaction, salt can change the location of surfactants at the isooctane/water interface, and significantly influence the aggregate behavior of AOT (diffusion coefficient increased, the value of peak radial distribution and concentration profile changed).2. The aggregate behavior of surfactant at the air/water interfaceThe aggregate behavior of octadecylamine (C18NH2·HCl) at the air/water interface was studied and the effects of the concentration of surfactant, the temperature, inorganic salts, and the pH value to the aggregate behavior of the system ware discussed. The simulation results showed that all of them significantly affected the aggregate behavior of the system except the temperature, and obviously changed in the concentration profile, the configuration of aggregate, the radial distribution function, and diffusion coefficient.We also studied the difference of aggregate behavior between Gemini surfactant C12C2C12 (12-2-12) and traditional single-chain surfactant (DTAB) at the air/water interface. Gemini surfactant is a new kind of surfactants, and has many unique properties compared with traditional surfactant, and was better than traditional surfactant in the physical and chemical properties, such as it have stronger surface activity, a lot of studies have been performed in experiment, but less in simulation. The reason that Gemini surfactant is prior to traditional surfactant can be obtained by comparing to the concentration profile, radial distribution function, and diffusion coefficient in microscopic scale.The aggregate behaviors of surfactant mixture system at the air/water were discussed in the last section. At first, we measure the surface tension of pure AOT and octadecylamine (C12BE) system, followed by measuring the surface tension of the mixture of AOT and C12BE and the mole ratio is 2:8,4:6, 6:4,and 8:2, respectively. At last, these systems were performed by all atom molecular dynamics simulation.The novelties of this paper:1) Simplify the experimental system of the aggregate of surfactant at the liquid/liquid and gas/liquid interface and give the all atom molecular dynamics simulation model.2) Combine the simulation and experiment, to explain the experimental phenomena with the simulation results, and also to prove our simulation results with the experimental results and data.3) Simulate the high surfactant concentration system, which it can't reach in the experiment and offer some views to forecast the experimental phenomena.