Surfactants molecular dynamics

Liu Z, Shang Y, Feng J, Peng C, Liu H, Hu Y Effect of hydrophilicity or hydrophobicity of polyelectrolyte on the interaction between polyelectrolyte and surfactants molecular dynamics simulations, y Phys Chem B 116(18) 5516—5526, 2012. 

H. Kovacs, A.E. Mark, J. Johansson, and W.F. van Gunsteren. The effect of environment on the stability of an integral membrane helix Molecular dynamics simulations of surfactant protein C in chloroform, methanol and water. J. Mol. Biol, 247 808-822, 1995. 

Surface tension is usually predicted using group additivity methods for neat liquids. It is much more difficult to predict the surface tension of a mixture, especially when surfactants are involved. Very large molecular dynamics or Monte Carlo simulations can also be used. Often, it is easier to measure surface tension in the laboratory than to compute it. 

The function / incorporates the screening effect of the surfactant, and is the surfactant density. The exponent x can be derived from the observation that the total interface area at late times should be proportional to p. In two dimensions, this implies R t) oc 1/ps and hence x = /n. The scaling form (20) was found to describe consistently data from Langevin simulations of systems with conserved order parameter (with n = 1/3) [217], systems which evolve according to hydrodynamic equations (with n = 1/2) [218], and also data from molecular dynamics of a microscopic off-lattice model (with n= 1/2) [155]. The data collapse has not been quite as good in Langevin simulations which include thermal noise [218]. 

In the past five years, it has been demonstrated that the QELS method is a versatile technique which can provide much information on interfacial molecular dynamics [3 9]. In this review, we intend to show interfacial behavior of molecules elucidated by the QELS method. In Section II, we present the principle and the experimental apparatus of the QELS along with the historical background. The dynamic collective behavior of molecules at liquid-liquid interfaces was first obtained by improving the time resolution of the QELS method. In Section III, we show the molecular collective behavior of surfactant molecules derived from the analysis of the time courses of capillary wave frequencies. Since the... 

Several recent molecular dynamics simulations (e.g. [10] and references therein) have focussed on the wetting of interfaces (Section 6.1) and, for example, the behaviour of very small droplets at the nanoscale. Such simulations are able to relate the atomistic behaviour directly to relevant macroscopic parameters such as the contact angle and are able to show the dramatic effects at this length scale of addition of surfactant molecules or roughening of the surface. 

The dispersion interaction between the surface active ions and the water-air interface was recently considered in the modeling of the equilibrium adsorption [62]. The molecular dynamic simulations are used in the recent years to describe the surfactant adsorption at the air-water interface [63-65],... 

Noticeable differences in conformation of surfactant lipoprotein assessed via Monte Carte simulation with implicit solvent and molecular dynamics in explicit solvent were observed. 

Recent molecular dynamics simulations of water between two surfactant (sodium dodecyl sulfate) layers, reported by Faraudo and Bresme,14 revealed oscillatory behaviors for both the polarization and the electric fields near a surface and that the two fields are not proportional to each other. While the nonmonotonic behavior again invalidated the Gruen—Marcelja model for the polarization, the nonproportionality suggested that a more complex dielectric response of water might, be at the origin of the hydration force. The latter conclusion was also supported by recent molecular dynamics simulations of Far audo and Bresme, who reported interactions between surfactant surfaces with a nonmonotonic dependence on distance.15... 

There are presently several groups around the world conducting molecular dynamics simulations of micellization and liquid crystallization of more or less realistic models of water, hydrocarbon, and surfactants. The memory and speed of a supercomputer required to produce reliably equilibrated microstructures constitute a challenge not yet met, in my opinion. By taking advantage of identified or hypothesized elemental structures one can, however, hope to learn a great deal about the dynamics and stability of the various identified microstructures. 

At room temperature, these molecules occupy well-defined locations in their respective crystal lattices. However, they tumble freely and isotropically (equally in all directions) in place at their lattice positions. As a result, their solid phase NMR spectra show features highly reminiscent of liquids. We will see an illustration of this point shortly. Other molecules may reorient anisotropically (as in solid benzene). Polymer segmental motions in the melt may cause rapid reorientation about the chain axis but only relatively slow reorientation of the chain axes themselves. Large molecular aggregates in solution (such as surfactant micelles or protein complexes or nucleic acids) may appear to have solidlike spectra if their tumbling rates are sufficiently slow. There are numerous other instances in which our macroscopic motions of solid and liquid may be at odds with the molecular dynamics. Nuclear magnetic resonance is one of the foremost ways of investigating these situations. 

Structure of Br may not be the same as that of the bulk. Some of the molecular dynamics calculations predict that halide anions in water tend to float on the surface of clusters consisting of water molecules rather than within water. This effect may cause a dissimilar solvation structure to that of the bulk. In addition, if the anion is segregated at the surface by surfactants such as large alkylammonium cations, the anion density at the surface should be high and its environment differ from the bulk. This is a preliminary report of the first experimental study of the solution surface by the EXAFS technique. This technique provides us information on the gas/liquid interface, the structure of Langmuir films, and the effect of the interface on chemical reactions. 

Model calculations of interface-solute electrostatic interactions reproduce well the view of microenvironment polarities of micelles and bilayers obtained from experimental data [57]. According to molecular dynamics simulations, at 1.2 nm from a bilayer interface, water has the properties of bulk water. At shorter distances, water movement slows as individual water molecules become attracted to the interface. At the true interface, which is a region containing both H2O molecules and the surfactant polar head groups, the water molecules are oriented with... 

M. Surridge, D. J. Tildesley, Y. C. Kong, and D. B. Adolf, A parallel molecular dynamics simulation code for dialkyl cationic surfactants. Parallel Comput., 22 (1996), 1053-1071. 

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