THE INTERFACIAL PROPERTIES AND DYNAMICS OF THE SDS-TYPE SURFACTANT MONOLAYER AT THE WATER/TCE INTERFACE: A MOLECULAR DYNAMICS SIMULATION STUDY
Today, microemulsions are receiving ever-increasing attention from both practical and theoretical points of view.14 Especially, because of their ability to encapsulate droplets of one material in another; micellar microemulsions may be useful in many applications, from nanoparticle self-assembly to drug delivery. Thus, an important first step to understand microemulsion is to have a molecular-level understanding of surfactant monolayer at interface. Despite the large number of thermodynamic as well as composition parameters, among the major issue concerning the surfactant monolayers at the interface between the binary immiscible fluids are the conformation of surfactant chain (i.e. packing, orientation, and order), interfacial properties (i.e. interfacial thickness, interfacial tension, area compressibility, and bending modulus) and their dependence on the chain length and the average area per surfactant molecule. Also, it is important to examine the interfacial dynamics of an interface saturated with surfactants. Via bending and pinching, the surfactant monolayer can generate aggregates characteristic of micellar microemulsion, which has a great potential of ordering nanoparticle and drug delivery by encapsulating nanoparticles into the core of micellar microemulsions and transferring from one matrix phase to another one. We perform a series of MD simulations on the category of sodium alkyl sulfate (SDS-type) surfactant monolayers at the water/trichloroethylene (TCE) interface with the increase of surface coverage. The simulation has clearly shown that the very dilute monolayer is well described as a two-dimensional gas. With the increase of interfacial surfactant coverage, the monolayer is in liquid-expanded (LE) phase. The surfactant tails at the interface become straighter, more ordered and thicker at higher surfactant coverage. With a further decrease in molecular areas, the monolayer with large negative surface tension becomes unstable. Our simulations show that buckling of the monolayer is of dynamic nature as a response to mechanical instability. The further transformation pathway from buckling to bud can be controlled by bending modulus, which depends crucially on the tail length and interfacial surfactant coverage. At a given area per molecule, the short tail chain makes the monolayer softer and the budding process becomes more probable. For the super-saturated softer SDS monolayer, the collapse transition is initiated by the buckling of monolayers, followed primarily by budding and detachment of the nanoscale swollen micelle from the monolayer.
Wen-xiong Shi Hong-xia Guo
Beijing National Laboratory Molecular Sciences (BNLMS),Joint Laboratory of Polymer Science and Materialsjnstitute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
国际会议
PP’2010，Jinan International Symposium on Polymer Physics(2010济南国际高分子物理学术研讨会)
济南
英文
350-351
2010-06-06（万方平台首次上网日期，不代表论文的发表时间）