293,867 research outputs found
Application of the z-transform to composite materials
Applications of the z-transform were made earlier to interfacial electron transfer involving semi-infinite solids, e.g., semiconductor/liquid and metal/liquid interfaces and scanning tunneling microscopy. It is shown how the method is readily adapted to treat composite materials, such as solid/solid interfaces or "molecular wire"/solid interfaces
Gas Enrichment at Liquid-Wall Interfaces
Molecular dynamics simulations of Lennard-Jones systems are performed to
study the effects of dissolved gas on liquid-wall and liquid-gas interfaces.
Gas enrichment at walls is observed which for hydrophobic walls can exceed more
than two orders of magnitude when compared to the gas density in the bulk
liquid. As a consequence, the liquid structure close to the wall is
considerably modified, leading to an enhanced wall slip. At liquid-gas
interfaces gas enrichment is found which reduces the surface tension.Comment: main changes compared to version 1: flow simulations are included as
well as different types of gase
Particles adsorbed at various non-aqueous liquid-liquid interfaces
Particles adsorbed at liquid interfaces are commonly used to stabilise water-oil Pickering emulsions and water-air foams. The fundamental understanding of the physics of particles adsorbed at water-air and water-oil interfaces is improving significantly due to novel techniques that enable the measurement of the contact angle of individual particles at a given interface. The case of non-aqueous interfaces and emulsions is less studied in the literature. Non-aqueous liquid-liquid interfaces in which water is replaced by other polar solvents have properties similar to those of water-oil interfaces. Nanocomposites of non-aqueous immiscible polymer blends containing inorganic particles at the interface are of great interest industrially and consequently more work has been devoted to them. By contrast, the behaviour of particles adsorbed at oil-oil interfaces in which both oils are immiscible and of low dielectric constant (ε < 3) is scarcely studied. Hydrophobic particles are required to stabilise these oil-oil emulsions due to their irreversible adsorption, high interfacial activity and elastic shell behaviour
Impedance spectroscopy of ions at liquid-liquid interfaces
The possibility to extract properties of an interface between two immiscible
liquids, e.g., electrolyte solutions or polyelectrolyte multilayers, by means
of impedance spectroscopy is investigated theoretically within a dynamic
density functional theory which is equivalent to the Nernst-Planck-Poisson
theory. A novel approach based on a two-step fitting procedure of an equivalent
circuit to impedance spectra is proposed which allows to uniquely separate bulk
and interfacial elements. Moreover, the proposed method avoids overfitting of
the bulk properties of the two liquids in contact and underfitting of the
interfacial properties, as they might occur for standard one-step procedures.
The key idea is to determine the bulk elements of the equivalent circuit in a
first step by fitting corresponding sub-circuits to the spectra of uniform
electrolyte solutions, and afterwards fitting the full equivalent circuit with
fixed bulk elements to the impedance spectrum containing the interface. This
approach is exemplified for an equivalent circuit which leads to a physically
intuitive qualitative behavior as well as to quantitively realistic values of
the interfacial elements. The proposed method is robust such that it can be
expected to be applicable to a wide class of systems with liquid-liquid
interfaces
Fluctuating Interfaces in Liquid Crystals
We review and compare recent work on the properties of fluctuating interfaces
between nematic and isotropic liquid-crystalline phases. Molecular dynamics and
Monte Carlo simulations have been carried out for systems of ellipsoids and
hard rods with aspect ratio 15:1, and the fluctuation spectrum of interface
positions (the capillary wave spectrum) has been analyzed. In addition, the
capillary wave spectrum has been calculated analytically within the Landau-de
Gennes theory. The theory predicts that the interfacial fluctuations can be
described in terms of a wave vector dependent interfacial tension, which is
anisotropic at small wavelengths (stiff director regime) and becomes isotropic
at large wavelengths (flexible director regime). After determining the elastic
constants in the nematic phase, theory and simulation can be compared
quantitatively. We obtain good agreement for the stiff director regime. The
crossover to the flexible director regime is expected at wavelengths of the
order of several thousand particle diameters, which was not accessible to our
simulations
Surface melting of methane and methane film on magnesium oxide
Experiments on surface melting of several organic materials have shown
contradictory results. We study the Van der Waals interactions between
interfaces in surface melting of the bulk CH_4 and interfacial melting of the
CH_4 film on the MgO substrate. This analysis is based on the theory of
Dzyaloshinskii, Lifshitz, and Pitaevskii for dispersion forces in materials
characterized by the frequency dependent dielectric functions. These functions
for magnesium oxide and methane are obtained from optical data using an
oscillator model of the dielectric response. The results show that a repulsive
interaction between the solid-liquid and liquid-vapor interfaces exists for the
bulk methane. We also found that the van der Waals forces between two
solid-liquid interfaces are attractive for the CH_4 film on the MgO substrate.
This implies that the van der Waals forces induce the presence of complete
surface melting for the bulk methane and the absence of interfacial melting for
CH_4 on the MgO substrate.Comment: 11 pages, 4 ps figure
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