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It is argued that the criticism by Faraji et al. is unfounded and clarified further why surface stress on a strain-free solid, as postulated by Shuttleworth, does not exist. [ABSTRACT FROM AUTHOR]

Theories of wetting have a long history and they are intensively used in interpreting experimental data. Nevertheless, many basic aspects, such as the pinning of a contact line and contact angle hysteresis, are still poorly understood. The development of a rigorous consensus theory has suffered from concepts that are based on faulty intuitions. These include the force interpretation of Young's equation, the use of the principle of minimizing the global free energy, and the concepts of the work of adhesion and the mechanical surface tension on a solid. In this paper, the appropriate treatment of the basic ingredients of surface thermodynamics is discussed and the route towards the physically justified theoretical approach on wetting is outlined. [ABSTRACT FROM AUTHOR]

Microparticle powders for nasal delivery were formulated to contain the model drug, zolmitriptan, and varying proportions of different polymers. The objective of the study was to investigate the effects of these formulative parameters on the surface chemistry of the spray-dried microparticles and their potential for adhesion to the tested substrates, porcine mucin, and nasal tissue. The polymers used were chitosans of varying ionization states and molecular weights and hydroxypropyl methyl cellulose. The surface energies of the surfaces of the microparticles were determined using contact angle measurements and the van Oss model. The theory of surface thermodynamics was applied to determine the theoretical potential for the different materials to adhere to the substrates. It was found that the drug or polymers alone, as well as the various formulations, were more likely to adhere to mucin than to nasal tissue. Further, there was a trend for higher molecular weight chitosans to adhere better to the substrates than lower molecular weight chitosans. Similarly, adhesion was improved for formulations with a higher content of polymers. These theoretical predictions may be compared with further experimental results and be of use in making informed decisions on the choice of formulations for future expensive bio-studies. [ABSTRACT FROM AUTHOR]

Abstract: We have determined the step edge free energy, the step edge stiffness and dimensionless inverse step edge stiffness of the highly kinked <010> oriented step on a (001) surface of a simple square lattice within the framework of a solid-on-solid model. We have found an exact expression for the step edge free energy in the case that only nearest neighbour interactions are taken into account. At low temperatures the dimensionless inverse step edge stiffness reduces to the universal value . However, with increasing temperature the dimensionless inverse step edge stiffness increases. Incorporation of an attractive next-nearest neighbour interaction leads to a suppression of the dimensionless inverse step edge stiffness. For a non-zero next-nearest neighbour interaction the dimensionless inverse step edge stiffness even vanishes at zero temperature. [Copyright &y& Elsevier]

Abstract: We show that three independent derivations of the Shuttleworth equation, arguably the second most important equation in surface physics, are inconsistent with Hermann’s mathematical structure of thermodynamics [R. Hermann, Geometry, Physics and Systems, Marcel Dekker Inc., New York, USA, 1973 (Chapter 6)]. The possible implications of this result are discussed. [Copyright &y& Elsevier]

Gibbs formulated a complete and general thermodynamics for surfaces in multicomponent fluid systems. When considering solid-fluid surfaces, he restricted attention to single-component solids in contact with fluids that could contain multiple components. Attempts that have been offered to generalize Gibbs' results for surfaces between multicomponent solids and fluid are problematic owing to the difficulty that the surface chemical potentials for components that also reside on substitutional lattice sites in the solids are not well defined. Therefore any expressions involving these surface chemical potentials, such as the conventional definition of the surface energy, will also not be well defined. In order to formulate a general thermodynamics of equilibrium that takes into account capillary effects in systems containing surfaces between a multicomponent solids and fluids, it is shown that the concept of thermodynamic availability (exergy) can be employed that, when applied to surfaces, depends on the extensive but not the intensive variables (such as the chemical potentials) of the surfaces. Using this approach, Gibbs-Thomson-Freundlich effects for finite-size solids, an adsorption equation for solid-fluid surfaces and the thermodynamics of nucleation during solidification can be treated in a straightforward manner without referring to the ill-defined surface chemical potentials. A derivation is given that appears to be the first one that properly generalizes Gibbs' analysis for the reversible work to form a critical nucleus to the case of solidification. [ABSTRACT FROM AUTHOR]

Abstract: We put forward a technique for calculating the surface segregation profile in substitutional disordered alloys. The surface internal energy and the effective bulk and surface chemical potentials are calculated using the full charge density exact muffin-tin orbitals method, combined with the coherent potential approximation. The application of our approach is demonstrated to the close-packed surface of Ag c Pd1−c random alloys with 0< c <1. The surface concentration profile, surface energy and segregation energy are investigated as functions of bulk composition. The present results are compared with former theoretical and experimental data. It is found that at low temperature, Ag segregates to the surface layer for the entire bulk composition range. At 0K, the subsurface layer contains 100% Pd for c ≲0.4, and somewhat more than (2c −1) Ag in alloys with c >0.5. The temperature dependence of the segregation profile is significant for Pd rich alloys and for alloys with intermediate concentrations. At temperatures ≳600K, the subsurface layer is obtained to be almost bulk like. [Copyright &y& Elsevier]

Abstract: Surface thermodynamic functions (surface entropy, surface enthalpy, and surface composition) of dilute solutions of 2-, 3-, and 4-methylcyclohexanol in ethylene glycol were obtained using surface tension measurements at various temperatures. Surface excess values and surface mole fractions were obtained from Gibbs equation and extended Langmuir model respectively. The results show that all methylcyclohexanols are surface active in ethylene glycol. The lyophobicity of solutes decreases with increasing temperature. The presence of a maximum point in the surface entropy diagram in all systems is explained by the formation of clathrate-like solvates at the surface of these systems. [Copyright &y& Elsevier]

The problem of size dependence of surface tension was investigated in view of a more general problem of the applicability of Gibbs’ thermodynamics to nanosized objects. For the first time, the effective surface tension (coinciding with the specific excess free energy for an equimolecular dividing surface) was calculated within a wide temperature range, from the melting temperature to the critical point, using the thermodynamic perturbation theory. Calculations were carried out for Lennard-Jones and metallic nanosized droplets. It was found that the effective surface tension decreases both, with temperature and particle size. [ABSTRACT FROM AUTHOR]

The problem of the applicability of the Gibbs thermodynamics to nanosized objects is investigated. It is shown that the Gibbs surface phases method may be extended to nanoparticles if the effective surface tension (the specific excess free energy) is interpreted as a function of the particle radius. The specific surface free energy (the surface tension) for nanodroplets and nanocrystals of noble gases and aluminum was calculated using the thermodynamic perturbation theory. It has been shown that the averaged surface tension decreases with the particle size both for small droplets and for nanocrystals. [Copyright &y& Elsevier]

The problem of applicability of thermodynamics to small objects has been investigated. It is shown that the Gibbs surface phase method may be extended to nanoparticles if the effective surface tension (the specific excess free energy) is interpreted as a function of the particle radius. [ABSTRACT FROM AUTHOR]

Thermodynamic stability conditions for nanoparticles (resulting from non-negativity of the second variation of the free energy) have been analyzed for two cases: (i) a nonvolatile nanosized particle with the size-dependent surface tension; (ii) the limiting case of larger objects when the surface tension takes its macroscopic value. It has been shown that the mechanical stability of a nanoparticle, i.e. its stability relative to the volume fluctuations, is defined by an interplay between the excess (“surface”) free energy and the volumetric elastic energy. According to the results obtained, noble gas clusters and metal nanoparticles satisfy the mechanical stability condition. At the same time, water nanodrops, as well as nanoparticles presented by nonpolar organic molecules, correspond to the stability limit. Among the investigated systems, the stability condition is not carried out for n-Pentane clusters. [ABSTRACT FROM AUTHOR]

The adhesion behaviour of Paenibacillus polymyxa bacteria on pyrite and chalcopyrite is examined by the surface thermodynamics and the extended DLVO theory approaches. In addition, the bacteria are adapted to pyrite and chalcopyrite minerals, and the adhesion behaviour of these bacteria is also investigated. The significance of acid–base interactions in adhesion is assessed. The essential parameters needed for the calculations of interaction energy between bacteria and mineral are experimentally determined. The results illustrate that the bacterial surfaces are more energetic than the mineral surfaces and the bacteria acquired acid–base surface energy component during their adaptation to mineral. The extended DLVO approach is found to be more effective in predicting the adhesion behaviour than the expectations from thermodynamic approach. The thermodynamic approach yields no bacterial adhesion on minerals and this discrepancy is the result of inadequate description of electrostatic interactions. The adhesion predictions by the DLVO approach are able to partially explain the bioflotation results of pyrite and chalcopyrite. Extended DLVO shows that on account of high bacterial surface energy, their aggregation is not feasible. But due to the hydrophobicity of pyrite and chalcopyrite, their aggregation is possible. [Copyright &y& Elsevier]