Dielectric Properties Tangential to the Interface in Model Insoluble Monolayers:  Theoretical Assessment

Abstract

Studies of insoluble monolayers built of phospholipids and various long-chained fatty acids or their glycerin esters are the major source for what is currently known about the relationship between monolayer composition and physicochemical properties. The surface pressure, dipole moment, dielectric permittivity, polarizability, refractivity, and other electrical and optical features are governed by the surfactant structural specificity and solvent organization at the microscopic level. To provide insight into the atomistic details of the interfacial structure, model monolayers at the air/water interface of two distinctly different in composition and isotherm profile surfactants are investigated by means of molecular dynamics all-atom simulations. Analysis of the computational results allows the estimation of empirically unattainable quantities such as tangential (di)electric properties, their decomposition to surfactant and water contributions, and their relationship with the changes in interfacial molecular organization at different surface concentrations. The employed theoretical approach provides a comprehensive description of interfacial phenomena at the molecular level where the traditional phenomenological investigations are ineffective.

Accurate Estimation of Membrane Capacitance from Atomistic Molecular Dynamics Simulations of Zwitterionic Lipid Bilayers

“…Equations and are the result of combining two different descriptions of the polarization and dipole moment vectors. Thus, combining their microscopic statistical mechanical description with the macroscopic continuum electrostatics one (where the dielectric tensor is defined as a proportionality constant) allows us to express the dielectric permittivity tensor in terms of the fluctuations in both vectors. ,− …”

Surface behavior of a model surfactant: A theoretical simulation study

“…Part of this deficiency can be overcome by theoretical simulations of surfactant monolayers, which have played an important role in investigating surfactant properties at the molecular scale [8]. In recent years, many simulation studies on the self-assembly behavior of amphiphilic molecules in the solution or at the interface were performed by applying various computational techniques including quantum mechanics (QM) [9,10], Monte Carlo (MC) [11][12][13], molecular dynamics (MD) [14][15][16], and Mesodyn simulation [17][18][19], or dissipative particle dynamics (DPD) simulations [20][21][22].…”

“…Although many approaches monitored the variation of surfactant organization during monolayer compression in the p/A isotherm, experiments have rarely focused on the dynamic process of surfactants moving from the bulk solution to the interface due to the difficult experimental conditions [4]. Although a number of analytical and phenomenological models were selected to interpret isothermic data or to describe surfactant monolayers at the interface [5][6][7], there is still a lack of techniques to exclusively probe changes at the interface at a molecular level [8]. The above models and experiments do not provide comprehensive molecular-level interpretation of interactions between surfactant and solvent molecules.…”

Theoretical description of 2D-cluster formation of nonionic surfactants at the air/water interface

“…Thus, Shushkov et al in ref. [76] studied the dielectrical parameters (tangential to the interface) for modeled monolayers of phospholipids and diglycerides of carboxylic acids at the vacuum/water interface depending on the area per molecule in the monolayer. They revealed a tendency to the decrease of the general tangential permittivity with the decrease of the surfactant motion freedom when compressing the monolayer.…”

“…The model of Bcoarse grains^is quite often used for modeling the surfactant or polymer behavior at different interfaces. This model is relatively new and popular for modeling the behavior of rather big surfactant molecules or polymers at large time-scales, when the molecule of interest is represented as a set of grains on springs containing one or several atomic groups [76].…”