The Prediction of Surface Tension and Thermodynamic Analysis of the Surface in Mixtures of Cryogenic Liquids

The surface tensions of 42 binary cryogenic mixtures at low temperature are correlated using the Shereshefsky model and excellent results are obtained. The average percent deviation is about ～ 1.08%. The Gibbs energy change in the surface region is calculated and is used to obtain the excess number of molecular layers in the surface region. Furthermore, the model is used to derive an equation for the standard Gibbs energy of adsorption. The experimental standard Gibbs energy of adsorption is obtained from surface tension data and compared with calculated data. The agreement between experimental and calculated data is found to be very good. The magnitude of the Gibbs energy change in the surface region and the standard Gibbs energy of adsorption are discussed in terms of nature and type of intermolecular interactions in binary mixtures.     

Contribution of concentration-dependent surface diffusion in ternary adsorption kinetics of ethane, propane and n-butane in activated carbon

The role of concentration-dependent surface diffusion in the adsorption kinetics of a multicomponent system is investigated in this paper. Ethane, propane and n-butane are selected as the model adsorbates and Ajax activated carbon as the model adsorbent. Adsorption equilibrium isotherm and dynamic parameters extracted from single-component systems are used to predict the ternary adsorption equilibria and kinetics. The effect of concentration-dependent surface diffusion on the adsorption kinetics predictions is studied by comparing the results of two mathematical models with the experimental data. Three diffusion mechanisms, macropore, surface and micropore diffusions are incorporated in both models. The distinction between these two models is the use of the chemical potential gradient as the driving force for the diffusion of the adsorbed species in one model and the concentration gradient in the other. It was found that the model using the chemical potential gradient provides a better prediction of the ternary adsorption kinetics data, suggesting the importance of the concentration dependency of the surface diffusion, which is implicitly reflected in the chemical potential gradient. The kinetic model predictions are also affected by the way how single-component adsorption equilibrium isotherm data are fitted.     

Green functions in the theory of semiconductor surfaces

Electronic properties of a few technologically important semiconductor surfaces, explored in surface Green function calculations, are presented and briefly discussed in comparison with experimental data from high-resolution surface spectroscopy. The emphasis is on results of first-principles calculations employing the local density approximation or the generalized gradient approximation of density functional theory. The systems addressed comprise of the prototype surfaces of the elemental semiconductors diamond and Si, as well as the group IV compound semiconductor SiC. The examples show that surface Green function calculations, as performed by Maria St licka and Sydney Davison in their early work on the surfaces of model systems, such as linear monoatomic chains or the Kronig–Penney model, can nowadays be applied to efficiently evaluate electronic properties of real surfaces. The results of such ab initio Green function calculations are found to be in very good agreement with experimental data.     

Increased stability and size of a bubble on a superhydrophobic surface

Computational and theoretical models of millimeter-sized bubbles placed on upright hydrophobic and superhydrophobic surfaces are compared with experimental data here. Although the experimental data for a hydrophobic surface corroborated the computational and theoretical data, the case of a superhydrophobic surface showed the bubbles to be able to contain significantly larger volumes than predicted. This is attributed to the greater ability of the bubble contact line to advance compared with its tendency to detach from the surface because of buoyancy. We surmise that a static model therefore describes only an unstable equilibrium for these bubbles, which unless heavily isolated from external influences are more likely to assume a larger stable size.     

Measurement of surface tension of desulfurization solution and thermodynamic model-(I)

According to the need of industrial design and application of new desulfurization technique, we determine surface tension of dilute SO₂ mixture gas in DMSO and DMSO?+?Mn²⁺ mixture absorbents, and establish their thermodynamic model based on experimental data, and the surface tension calculated by the model shows good agreement with experimental data.     

Surface tension of different sized single-component droplets,according to macroscopic data obtained using the lattice gas model and the critical droplet size during phase formation

Size dependences of the surface tension of spherical single-component droplets are calculated using equations of the lattice gas model for 19 compounds. Parameters of the model are found from experimental data on the surface tension of these compounds for a macroscopic planar surface. The chosen low-molecular compounds satisfy the law of corresponding states. To improve agreement with the experimental data, Lennard-Jones potential parameters are varied within 10% deviations. The surface tensions of different sized equilibrium droplets are calculated at elevated and lowered temperatures. It is found that the surface tension of droplets grows monotonically as the droplet size increases from zero to its bulk value. The droplet size R ₀ corresponding to zero surface tension corresponds to the critical size of the emergence of a new phase. The critical droplet sizes in the new phase of the considered compounds are estimated for the first time.     

Atomistic model of micelle-templated mesoporous silicas: structural, morphological, and adsorption properties

The structural, morphological, and adsorption properties of MCM-41 porous silicas are investigated using a realistic numerical model obtained by means of ab initio calculations [Ugliengo, P.; et al. Adv. Mater.2008, 20, 1]. Simulated X-ray diffraction, small angle neutron scattering, and electronic microscopy for the atomistic model are in good agreement with experimental data. The morphological features are also assessed from chord length distributions and porous volume and specific geometrical surface calculations, etc. The N(2), CO(2), and H(2)O adsorption isotherms in the atomistic model of MCM-41 are also in reasonable agreement with their experimental counterpart. An important finding of the present work is that water forms a film adsorbed on specific hydrophilic regions of the surface while the rest of the surface is depleted in water molecules. This result suggests that the surface of MCM-41 materials is heterogeneous, as it is made up of both hydrophilic and hydrophobic patches. While adsorption and irreversible capillary condensation can be described using the thermodynamical approach by Derjaguin (also known as the Derjaguin-Broekhoff-De Boer model), the Freundlich equation fits nicely the data for reversible and continuous filling in small pores.     

Modeling of catalytic coke formation in thermal cracking reactors

At the start-up period, the most important mechanism in the coke production with a clean reactor surface is the catalytic mechanism. The study of this mechanism can be very useful for the better comprehension of the coke production process. In this paper, a model was designed for such a production through the utilization of a catalytic mechanism and a kinetic model, capable of interpreting the catalytic coke production on the reactor surface. For the determination of the model reliability, the experimental data related to the naphtha feed, existing in literature, were used. In addition, the constant parameters of the model, the velocity and the activation energy constants, associated to the kinetic model, were calculated. The results of the developed model were in satisfactory agreement with the experimental data. Eventually, the catalytic coke amount in comparison with the total coke production on the reactor surface and its significance were under investigation.     

Molecular surface and order parameters in liquid crystals

The surface model for solute ordering in nematics, which is based on the decomposition of the orientational potential according to the contributions of surface elements, leads to a simple procedure for the calculation of both orientational properties and the cholesteric order induced by a chiral compound. However, a realistic representation of the molecular surface accessible to the solvent is required. The rolling sphere algorithm, applied to the ensemble of atomic van der Waals spheres of a molecule, provides a natural determination of such a surface, sinceit smoothes away the smallscaledetails. Thesurfaceordering model implemented with the rolling sphere smoothing of the surface is described and applied to several molecular systems. It is shown that the orientational order parameters are substantially independent of the rolling sphere radius identified with the average curvature of the solvent molecular surface. On the contrary, a sensible dependence on such a parameter emerges for the chirality order parameter, this behaviour pointing out the role of the shape of solvent molecules in the chirality recognition of solutes. A fair agreement is obtained in the comparison with experimental data.     

Modelling interfacial properties of binary and ternary liquid mixtures of tetrahydrofuran, 2-propanol and 2,2,4-trimethylpentane

The present modelling study has been dedicated to determining the interfacial properties of binary and ternary liquid mixtures made up of tetrahydrofuran, 2-propanol and 2,2,4-trimethylpentane. The variation of the temperature is from 288 to 308 K. By using both UNIFAC activity model and the fugacity model based on the cubic plus association (CPA) equation of state (EOS), a model based on the equality of chemical potentials in the liquid and the surface layer is utilised to describe the liquid–vapour interface of these liquid mixtures. The surface tension, composition and density are simultaneously predicted. The results of this model show that experimental surface tension data are in a good agreement with the predicted ones. The model using CPA EOS and molar volume has a better performance than the one uses the UNIFAC activity model.     

Adsorption of polar substances from binary and ternary mixtures on silica gel

The adsorption isotherms of acetone and methyl ethyl ketone from binary and ternary mixtures in benzene and n-heptane on silica gel were measured. The experimental adsorption data are discussed on the basis of changes of the composition of mixed solvent (benzene + n-heptane) in ternary mixtures. It has been found that the different structures of the surface phase correspond to the system investigated. The marked dependence of the adsorption on the solvent character is demonstrated. For benzene and ternary (ketone + benzene + n-heptane) mixtures a mixed character of the surface phase is observed whose composition is determined by competition of liquid components for silica surface as well as its tendency to complex. Bilayer model of the surface phase gives a good representation of the experimental data for binary systems benzene + ketone.     

Spatio-temporal organization in alloy electrodeposition: a morphochemical mathematical model and its experimental validation

This paper proposes a novel mathematical model for the formation of spatio-temporal patterns in electrodeposition. At variance with classical modelling approaches that are based on systems of reaction–diffusion equations just for chemical species, this model accounts for the coupling between surface morphology and surface composition as a means of understanding the formation of morphological patterns found in electroplating. The innovative version of the model described in this work contains an original, flexible and physically straightforward electrochemical source term, able to account for charge transfer and mass transport: adsorbate-induced effects on kinetic parameters are naturally incorporated in the adopted formalism. The relevant non-linear dynamics is investigated from both the analytical and numerical points of view. Mathematical modelling work is accompanied by an extensive, critical review of the literature on spatio-temporal pattern formation in alloy electrodeposition: published morphologies have been used as a benchmark for the validation of our model. Moreover, original experimental data are presented—and simulated with our model—on the formation of broken spiral patterns in Ni–P–W–Bi electrodeposition.     

The cavity models and the curvature dependence of the surface tension. Spherical cavities in anisotropic solvents

In the present work the solution process of globular solutes (xenon, cyclohexane, cyclooctane and adamantane) in n-alkane solvents is analyzed. New experimental data on solution enthalpies of adamantane in those solvents are presented. The cavity model previously proposed is corrected with respect to the dependence of the surface tension on the curvature radius of the microscopic cavity and a new equation is proposed to describe this dependence.     

Abrasively modified electrodes: mathematical modelling and numerical simulation of electrochemical dissolution/growth processes under cyclic voltammetric conditions

An approximate mathematical model for electrochemical dissolution/growth processes of diffusionally independent and well-separated particles randomly dispersed on an inert conducting electrode surface is presented and solved using numerical simulation. The model, mimicking abrasively modified electrodes where particles of electroactive voltammograms solid are immobilised on an electrode surface, provides clear insights into the effects of different parameters on the voltammetric response of such systems and permits the exploration of the competition taking place between mass transport and surface processes. The mathematical model is then compared with experimental data obtained with basal plane pyrolytic graphite electrode abrasively modified with solid particles of perinaphthenone and studied in aqueous solution.Dedicated to Professor Dr. Alan M. Bond on the occasion of his 60th birthday.     

Comparison of various models describing the adsorption of surfactant molecules capable of interfacial reorientation

The thermodynamic model for describing the adsorption of surfactant molecules in different adsorption states, the reorientation model, is reconsidered on a more rigorous level. The resulting model equations are used to describe experimental surface pressure data published in the literature. The new model proposed contains three physical parameters and describes the experimental dependencies Pi(c) for oxethylated alcohols very accurately.