Molecular Dynamics Simulation of Surfactant Microaggregates in the Apolar Medium of n-Octane

Abstract

Molecular dynamics simulation of reverse micelles of a cationic surfactant and water clusters in n -octane is performed. The main structural and thermodynamic characteristics of the systems are obtained. On average, the micelles have a spherical shape. The partial ion distribution densities virtually coincide, indicating the formation of stable ion pairs. The local profiles of the component distribution densities make it possible to establish that both water and oil slightly penetrate into the region where the hydrophobic portion of the surfactant is located. Separate cation-anion complexes dissolve in the aqueous cavity of a micelle. The hydration shells of the ions overlap; at the same time, the first hydration shell contains up to three water molecules. The energy contributions of each of the components to their force interaction are characterized in detail. The principal contribution to the internal energy for micelles is due to electrostatic interaction between the surfactant molecules. The local normal pressure is calculated, and its value is used to estimate the effective surface tension for the systems in question.

Computer simulation of reverse micelles and water-in-oil microemulsions

“…The destruc tion of the hydrogen network was related to the fact that the micelle core is geometrically confined and the translational and, especially, rotational motion of water molecules is hindered in it. The data obtained were in good qualitative agreement with the conclu sions drawn earlier for simpler models [9,[17][18][19][20][21][22][23][24][25][26][27]. The authors of [32] confirmed the data on the layered structure of water near an interfacial surface, and observed the transfer of water from the micelle core to the hydrocarbon phase.…”

“…The application of molecular simulation, Monte Carlo (MC), and molecular dynamics (MD) methods [9][10][11][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] provides the most detailed information on the structural and thermodynamic characteristics of small systems with curved interfaces and on the properties of micellar aggregates in surfac tant solutions. In addition to the thermodynamic characteristics, the MD method enables one to deter mine the dynamic parameters of individual compo nents of micelles.…”

Geometric characteristics of micellar systems as precursors of lanthanide-containing lyotropic mesophases

“…40 The final structure of the surfactant molecule with allowance for thermodynamic parameters was determined by the MD method, which has been successfully used in modeling of micellar systems and for the determination of geometric parameters and thermodynamic character istics. 41, 42 For convenience of calculations, processing of the results obtained, and reduction of the computing time, the effects of solvent on the polar and nonpolar fragments of the surfactant molecule were analyzed separately. The surfactant molecule was conditionally divided into two fragments, the hydrocarbon "tail" (C 12 H 25 -) and the po lar group (-O(CH 2 CH 2 O) 10 H).…”

Where Are Sodium Ions in AOT Reverse Micelles? Fluoride Anion Probes Nanoconfined Ions by 19F Nuclear Magnetic Resonance Spectroscopy

“…Here, we present the first experimental demonstration that sodium ions reside near or at the inner interface in AOT reverse micelles. These results are consistent with a range of other measurements on AOT reverse micelles that find differences in the nature of water in interfacial and interior locations and its heterogeneous nature compared to the homogeneous nature of bulk aqueous solutions. − ,− ,− ,,,,, …”

“…This also suggests that there is a propensity for the surfactant counterions to migrate to the interface. 7,23−27 Simulations by both Abel et al 11 as well as Mudzhikova and Brodskaya 12 and Chowdhary and Ladanyi all show that the AOT sulfur atom always has at least one sodium cation as a nearest neighbor.…”