Search results for "Gibbs isotherm"
showing 10 items of 11 documents
Thermodynamic properties of a liquid–vapor interface in a two-component system
2010
Abstract We report a complete set of thermodynamic properties of the interface layer between liquid and vapor two-component mixtures, using molecular dynamics. The mixtures consist of particles which have identical masses and diameters and interact with a long-range Lennard-Jones spline potential. The potential depths in dimensionless units for like interactions is 1 (for component 1) and 0.8 (for component 2). The surface excess entropy decreases when the temperature increases, so the surface has a negative excess heat capacity. This is a consequence of the fact that the surface tension decreases to zero at the critical point, proportional to ( T C , i − T ) 2 ν . The surface entropy decre…
Surface tension and density of binary mixtures of monoalcohols, water and acetonitrile: equation of correlation of the surface tension
2009
Measurements of the surface tension (σ) and density (ρ) of binary mixtures of monoalcohols, water and acetonitrile at 298.15 K and at atmospheric pressure, as a function of mole fraction (x) have been made. The experimental values of the deviation of surface tension and the excess of molar volume (Δσ, V E) have been correlated by the Redlich–Kister equation. An empirical correlation equation is presented for the study of the surface tension of these mixtures, and comparisons are made of the experimental values of surface tension versus those obtained with the correlation equation and with other models of correlation. Finally, with the purpose of corroborating the validity of the correlation…
Model calculations for wetting transitions in polymer mixtures
1985
Partially compatible binary mixtures of linear flexible polymers are considered in the presence of a wall which preferentially adsorbs one component. Using a Flory-Huggins type mean field approach, it is shown that in typical cases at two-phase coexistence the wall is always « wet », i.e. coated with a macroscopically thick layer of the preferred phase, and the transition to the non wet state occurs at volume fractions of the order of 1/~N (where N is the chain length) at the coexistence curve. Both first and second order wetting transitions are found, and the variation of the surface layer thickness, surface excess energy and related quantities through the transition is studied. We discuss…
In-situ radiotracer studies of sorption processes in solutions containing (bi)sulfite ions—II. Low carbon steel
1997
Abstract In this paper, time, potential and pH dependence of SO42− and HSO3− accumulations measured by an in-situ radiotracer method on surface oxide layers of low carbon steel are presented and discussed. This work is a continuation of a research program[1–5] and deals with the characterization of the sorption behaviour of low carbon steel in solutions containing sulfate and bisulfite ions (as a possible model of acid rain). From the experimental results it can be stated that 1. (i) the presence of bisulfite ions in the solution phase accelerates the corrosion of low carbon steel; 2. (ii) at E > 0.40 V the electrooxidation of HSO3− ions presumably proceeds to yield a steel surface covered …
Transport coefficients of n-butane into and through the surface of silicalite-1 from non-equilibrium molecular dynamics study
2009
We have studied coupled heat and mass transfer of n-butane through a membrane of silicalite-1. A description of the surface was given using non-equilibrium thermodynamics, and transport coefficients were determined. Three independent coefficients were found for the whole surface: the resistance to heat transfer, the coupling coefficient and the resistance to mass transfer. These coefficients were defined in stationary state. All resistances are significant, and show that the surface acts as a barrier to transport. A new scheme was devised to find the enthalpy of adsorption, from two particular coupling coefficients, namely the measurable heats of transfer. The method yields the enthalpy of …
Chapter III Phase transitions at surfaces
1995
Abstract The statistical mechanics of phase transitions is briefly reviewed, with an emphasis on surfaces. Flat surfaces of crystals may act as a substrate for adsorption of two-dimensional (d=2) monolayers and multilayers, offering thus the possibility to study phase transitions in restricted dimensionality. Critical phenomena for special universality classes can thus be investigated which have no counterpart in d=3. Also phase transitions can occur that are in a sense “in between” different dimensionalities (e.g., multilayer adsorption and wetting phenomena are transitions in between two and three dimensions, while adsorption of monolayers on stepped surfaces allows phenomena in between o…
Second inflection point of water surface tension in the deeply supercooled regime revealed by entropy anomaly and surface structure using molecular d…
2019
The surface tension of supercooled water is of fundamental importance in physical chemistry and materials and atmospheric sciences. Controversy, however, exists over its temperature dependence in the supercooled regime, especially on the existence of the second inflection point (SIP). Here, we use molecular dynamics simulations of the SPC/E water model to study the surface tension of water (sigma(w)) as a function of temperature down to 198.15 K, and find a minimum point of surface excess entropy per unit area around approximate to 240-250 K. Additional simulations with the TIP4P/2005 water model also show consistent results. Hence, we predict an SIP of sigma(w) roughly in this region, at t…
Polymeric matrix hydrophobicity governs saponin packing-density on nanoparticle surface and the subsequent biological interactions.
2020
Abstract This study investigated the loading behavior of Quillaja saponin as a model surface-active cargo on (NP) nanoparticles prepared with various hydrophobic polymers and using different organic solvents through emulsification/solvent evaporation, and the impact of NP surface hydrophobicity upon the cytotoxic and hemolytic properties of the loaded entity. A superficial monolayered arrangement of saponins on NP was established (R2 > 0.9) for all NP, as the saponin loading values complied with the Langmuir adsorption isotherm over the entire concentration range. Next, based on the measurement of interfacial tension between formulation phases, and the subsequent use of Gibb’s adsorption is…
Dynamics of multilayer adsorption: a Monte Carlo simulation
1992
Abstract The growth of an adsorbed film at an initially empty surface which is exposed at time t = 0 to a gas is studied within the framework of a kinetic lattice gas model by Monte Carlo simulation. The model includes an attractive potential V ( z ) between adsorbed particles at distance z from the surface, V(z) = −A z 3 and a nearest-neighbor attractive interaction between the gas atoms. Several choices of the surface potential depth A , corresponding to different sequence of layering transitions, are considered. The Monte Carlo process assumes random evaporation/condensation events of gas atoms in adsorbed layers close to the surface, while surface diffusion is disregarded. For temperatu…
Controlling the wetting properties of the Asakura-Oosawa model and applications to spherical confinement.
2012
We demonstrate for the Asakura-Oosawa model and an extension of this model that uses continuous rather than hard potentials, how wetting properties at walls can be easily controlled. By increasing the interaction range of the repulsive wall potential acting on the colloids (while keeping the polymer-wall interactions constant) polymers begin to substitute colloids at walls and the system can be driven from complete wetting of colloids via partial wetting to complete wetting of polymers. As an application, we discuss the morphology and wetting behavior of colloid-polymer mixtures in spherical confinement. We apply the recently developed 'ensemble switch method' where the Hamiltonian is exten…