Adhesive transitions in Newton black films: A computer simulation study

Abstract

We report molecular dynamics simulations of Newton black films (NBFs), ultra thin films of aqueous solutions stabilized with two monolayers of ionic surfactants, sodium dodecyl sulfate. We show that at low water content conditions and areas per surfactant corresponding to experimental estimates in NBFs, homogeneous films undergo an adhesion "transition," which results in a very thin adhesive film coexisting with a thicker film. We identify the adhesive film with the equilibrium structure of the Newton black film. We provide here a direct microscopic view of the formation of these important structures, which have been observed in experimental studies of emulsions and foams. We also report a detailed investigation of the structural properties and interfacial fluctuation spectrum of the adhesive film. Our analysis relies on the definition of an "intrinsic surface," which is used to remove the averaging effect that the capillary waves have on the film properties.

Intrinsic profiles and the structure of liquid surfaces

“…That difficulty is also observed within the ISM, since γ(q) is much more sensitive thañ ρ(z; q u ) to the choice of method and parameters. The application to more complex interfaces, like amphiphiles on water-oil and water-vapor interfaces [38], or bilayer membranes [39] are providing cleaner results, because the definition of surface pivots does not rely on the choice of percolation parameters. Moreover the intrinsic surfaces associated to different molecular sites help to separate the global undulating mode from the inner deformations of the interfacial region.…”

The structure of ionic aqueous solutions at interfaces: An intrinsic structure analysis

“…These algorithms eliminate the averaging effect of thermal fluctuations. 30,31 This approach, and similar ones, [32][33][34] have been applied to a number of fluid interfaces; simple fluids, 35 water, 36,37 alkali fluids, 38 oil-water interfaces, 32, 39-41 hydrophilic interfaces, 42 and molten salts. 43 The intrinsic profile offers a higher level of resolution of the interface, and, unlike the mean profiles, it is independent of the interfacial cross sectional area used in the simulations.…”

Layer-by-layer and intrinsic analysis of molecular and thermodynamic properties across soft interfaces

“…For example, the intrinsic analysis has been essential to the investigation of surface properties of ionic liquids, [20][21][22][23] explanation of the surface tension anomaly of water, 24,25 immersion depth of surfactants in water, 26 oil-water interfaces, 27 structure of ionic aqueous solutions and their intrinsic interfacial potential, 28 the plausibility of the "HCN World" hypothesis, 29 as well as the adhesive properties of Newton black films. 30 Besides the exact location of the intrinsic surface itself, these methods provide in addition the full list of surface molecules. Thus, by removing the molecules constituting the surface layer and repeating the whole procedure, the molecules of the second layer beneath the surface can also be identified.…”