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Type: Artigo de periódico
Title: Molecular dynamics simulations of AOT-water/formamide reverse micelles: Structural and dynamical properties
Author: Pomata, MHH
Laria, D
Skaf, MS
Elola, MD
Abstract: We present results from molecular dynamics simulations performed on reverse micelles immersed in cyclohexane. Three different inner polar phases are considered: water (W), formamide (FM), and an equimolar mixture of the two solvents. In all cases, the surfactant was sodium bis(2-ethylhexyl) sulfosuccinate (usually known as AOT). The initial radii of the micelles were R similar to 15 A, while the corresponding polar solvent-to-surfactant molar ratios were intermediate between w(0)=4.3 for FM and w(0)=7 for W. The resulting overall shapes of the micelles resemble distorted ellipsoids, with average eccentricities of the order of similar to 0.75. Moreover, the pattern of the surfactant layer separating the inner pool from the non-polar phase looks highly irregular, with a roughness characterized by length scales comparable to the micelle radii. Solvent dipole orientation polarization along radial directions exhibit steady growths as one moves from central positions toward head group locations. Local density correlations within the micelles indicate preferential solvation of sodium ionic species by water, in contrast to the behavior found in bulk equimolar mixtures. Still, a sizable fraction of similar to 90% of Na(+) remains associated with the head groups. Compared to bulk results, the translational and rotational modes of the confined solvents exhibit important retardations, most notably those operated in rotational motions where the characteristic time scales may be up to 50 times larger. Modifications of the intramolecular connectivity expressed in terms of the average number of hydrogen bonds and their lifetimes are also discussed.
Subject: colloids
hydrogen bonds
liquid structure
liquid theory
molecular dynamics method
organic compounds
Country: EUA
Editor: Amer Inst Physics
Rights: aberto
Identifier DOI: 10.1063/1.3042275
Date Issue: 2008
Appears in Collections:Unicamp - Artigos e Outros Documentos

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