Electrostatic potential and counterion partition between flat and spherical interfaces

Autor(es)

Bernardino, Kalil ^[1] ; de Moura, Andre Farias ^[2]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Chem, Sao Paulo, SP - Brazil

^[2] Univ Fed Sao Carlos, Dept Chem, Sao Carlos, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Journal of Chemical Physics; v. 150, n. 7 FEB 21 2019.
• Citações Web of Science: 0

Resumo

While the electrostatic potential and the counterion distribution produced by interfaces with idealized geometries can be well-described by analytical models, the same does not hold true for the interaction between surfaces with different and arbitrary geometries. Besides, the geometry of a charged interface may also affect the counterion adsorption, potentially modulating the electrostatic potential and the solvent organization close to the interfaces, demanding molecular details to be taken into account. The complex electrostatics of a sodium dodecyl sulfate micelle in the presence of monolayers of the same surfactant at the water-vapor interface was assessed by a set of molecular dynamics simulations. The electrostatic potential was evaluated numerically, and its total magnitude was decomposed into contributions arising from each species comprising the system. The counterion adsorption was stronger at the flat interfaces due to the more favorable formation of sodium bridges, where the same counterion is bounded to two or more anionic heads, while water reorientation was more pronounced near the micelle. These opposing effects counteracted each other so that the overall electrostatic potential changes were similar for both interfaces. The increase in the counterion concentration between the micelle and the interface originates a double layer mediated repulsion amounting to a free energy barrier of at least 14 kJ/mol, preventing the micelle to get closer to the monolayers. It is noteworthy that the hydrophobic regions had electrostatic potential contributions as large as those arising from the hydrophilic regions, mostly due to the orderly orientation of the terminal methyl groups. Published under license by AIP Publishing. (AU)

• Processo FAPESP: 17/12063-8 - Dinâmica molecular de não-equilíbrio de líquidos iônicos
• Beneficiário: Kalil Bernardino
• Linha de fomento: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 13/07296-2 - CDMF - Centro de Desenvolvimento de Materiais Funcionais
• Beneficiário: Elson Longo da Silva
• Linha de fomento: Auxílio à Pesquisa - Centros de Pesquisa, Inovação e Difusão - CEPIDs
• Processo FAPESP: 12/15147-4 - Estudo computacional da termodinâmica de associação de sistemas auto-organizados
• Beneficiário: André Farias de Moura
• Linha de fomento: Auxílio à Pesquisa - Regular