Surface tension multicomponent system

We expect more insight from simulations in the future, particularly in situations where these multicomponent systems show effects of coupling between the different degrees of freedom, surface tensions depending on temperature and concentration, hydrodynamic flow induced by concentration gradients in addition to thermal buoyancy. 

The National Institute of Standards and Technology (NIST) molten salts database has been designed to provide engineers and scientists with rapid access to critically evaluated data for inorganic salts in the molten state. Properties include density, viscosity, electrical conductance, and surface tension. Properties for approximately 320 single salts and 4000 multicomponent systems are included, the latter being primarily binary. Data have been abstracted from the literature over the period 1890-1990. The primary data sources are the National Bureau of Standards-National... 

In general, for a multicomponent system, there are (C — 1) different ri(1) to be evaluated. We can measure the surface tension of a series of solutions in each of which the mole fraction of one of the components is slightly different from that in all of the other solutions while the values of the other (C — 2) independent mole fractions are the same. There would be C solutions. By taking the differences between the surface tensions and between the mole fractions and applying these differences to Equation (13.63), we obtain (C — 1) independent equations, from which the value of each rj(1) can be calculated. 

For multicomponent systems, the expression for y here employed may be shown equivalent to that involved in the cluster diagram technique (6), which is currently being employed in a variety of problems. The present derivation shows that the starting expressions satisfy the thermodynamic consistency relation embodied by the adsorption isotherm. It is, however, important to observe that any direct application of these alternative rigorous approaches, which is of necessity of an approximate nature, leads to some violation of the complete internal equilibrium conditions. Similarly, calculations of surface tension which employ the adsorption equation as a starting point invariably violate mechanical equilibrium in some order of approximation. 

The extension of the CNT to homogeneous nucleation in atmospheric, essentially multicomponent, systems have faced significant problems due to difficulties in determining the activity coefficients, surface tension and density of binary and ternary solutions. The BHN and THN theories have been experiences a number of modifications and updates. At the present time, the updated quasi-steady state BHN model [16] and kinetic quasi-imary nucleation theory [24,66], and classical THN theory [25,33] and kinetic THN model constrained by the experimental data... 

Nucleation in the atmosphere is essentially multicomponent process. However, a commonly used classical approach incapable of the quantitative treatment of multicomponent systems due to (a) excessive sensitivity to poorly defined activity coefficients, density and surface tension of multicomponent solutions (b) strong dependence of nucleation rates on thermochemistry of initial growth steps where... 

Surface tensions can also be used to predict the behavior of multicomponent solid systems. Unlike single-component systems, the surface tension is no longer equal to the surface free energy G, but is related to the different component concentrations at the smface by the Gibbs equation ... 

Chap. 2, altered surface tensions of surface-treated polymers are directly accessible. In addition, laterally resolved maps of adhesive interactions are useful to investigate heterogeneous samples, such as multicomponent systems, or to record local functional group distributions. For quantitative AFM work, calibration procedures for the cantilever spring constant and the AFM detection system become important. In addition, the use of modified tips will be discussed as a means to enhance the applicability of AFM for chemically sensitive imaging. 

We see that the shear- (i.e., tangential-) stress components are discontinuous across the interface whenever gradv y is nonzero. Now, the interfacial tension for a two-fluid system, made up of two pure bulk fluids, is a function of the local thermodynamic state - namely, the temperature and pressure. However, it is much more sensitive to the temperature than to the pressure, and it is generally assumed to be a function of temperature only. If the two-fluid system is a multicomponent system, it is often the case that there may be a preferential concentration of one or more of the components at the interface (for example, we may consider a system of pure A and pure B, which are immiscible, with a third solute component C that is soluble in A and/or B but that is preferentially attracted to the interface), and then the interfacial tension will also be a function of the (surface-excess) concentration of these solute components. Both the temperature and the concentrations of adsorbed species can be functions of position on the interface, thus leading to spatial gradients of y. 

The surface tension of a multicomponent system changes as the surface concentrations of its various constituents are altered. Rigorous derivation of the variation of surface tension with surface excess concentration yields... 

During the last few years, attention shifted toward the glassy state, where the performance depends on the extent of freezing the free-volume parameter. The physical aging of vitreous multicomponent systems was interpreted successfully by means of the S-S equation of state. These aspects, along with applications of the S-S equation of state to surface tension and to PALS, are discussed in Chapter 8 and Chapters 10-12, respectively. 

Marangoni effects can be encountered in both single- and multicomponent liquid systems. In a pure liquid, surface tension gradients result from differences in temperature (or evaporation rate) from one point to another in the system. It is generally found that an increase in temperature lowers ctlv so that where hot spots occur, liquid flows away to cooler regions of the liquid (Fig. 6.13 ). The result of such a phenomenon can be the formation of dimples in a surface that dries or solidifies under uneven temperature conditions. 

In multicomponent systems (e.g., surfactant solutions), surface tension gradients usually are due to adsorption-related phenomena or, where possible, to different rates of evaporation from the system (although simple temperature variations can also be important). If the system contains two liquid components of differing volatility, the more volatile liquid may evaporate more quickly from the LV interface, resulting in localized compositional—and therefore surface tension—differences. It is also commonly found that when two or more components are present, one will be preferentially adsorbed at the LV interface and lower ctlv of the system. If a surface-active component... 

Multicomponent systems may also involve the selective adsorption of one component at the SL interface. Since the component that lowers the interfacial tension will be preferentially adsorbed, the rate of the adsorption process can affect the local tension and the contact angle. In many systems, the rate of adsorption at the solid surface is found to be quite slow compared to the rate of movement of the SLV contact line. As a result, the system does not have time for the various interfacial tensions to achieve their equilibrium values. Most surfactants, for example, require several seconds to attain adsorption equihbrium at a LV interface, and longer times at the SL interface. Therefore, if the hquid is flowing across fresh solid surface, or over any surface at a rate faster than the SL adsorption rate, the effective values of olv and osl (and therefore 6) will not be the equilibrium values one might obtain from more static measurements. More will be said about dynamic contact angles in later chapters. 

The surface tension of water diminishes when a surfactant, even in small quantities, is added. Similarly, an adsorbed gas reduces the surface energy of a solid. The Gibbs equation provides a relation between surface tension and surface concentration in multicomponent systems. 

By comparison with (3.16) and subsequent division by dA, we obtain an equation that relates the surface free energy to the surface tension for a multicomponent system ... 

Aseyev, GG. ( 99S) Electrolytes. Properties of Solutions. Methods for Calculation of Multicomponent Systems and Experimental Data on Thermal Conductivity and Surface Tension. Begell-House Inc., New York. 

The thermodynamics of curved surfaces is more subtle than that of planar, and we discuss only the most important case, the spherical surface, for which the two principal radii of curvature are equal. Hie extension of the argument to other curved surfaces is beset with difficulties into which we do not enter. The spherical surface, the bubble or the drop, is the only one that is stable in ffie absence of an external field. The original analysis of Gibbs was clarified and its consequences worked out by Tolman, whose work Koenig extended to multicomponent systems. Buff, Hill, and Kondo describe explicitly how the surface tension depends on the position of the dividing surface to which it is referred, or at which it is calculated. 

The parachor method is one of the most commonly used correlations for the surface tensions. The method was originally suggested by MacLeod [50] and Sugden [51] for a singlecomponent fluid and was extended to multicomponent systems by Weinaug and Katz [52]. An expression for the surface tension in this method is... 

Point defects segregate to planar defects just as they do to linear defects. Adsorption on surfaces and the related catalysis of reactions on surfaces are well-known phenomena. The amount of segregation is related to the reduction in surface tension y for the boundary by the Gibbs adsorption equation, which for a multicomponent system is... 

The interfacial tension can undergo significant changes if the polarity of the medium is altered, such as in the stability/coagulation transition caused by the addition of water to hydrophobic silica dispersions in propanol or ethanol [44,52,53]. Also, the addition of small additives of various surface-active substances can have a dramatic effect on the structure and properties of disperse systems and the conditions of transitions [14,16,17,26]. The formation and structure of stable micellar systems and various surfactant association colloids, such as microemulsion systems and liquid crystalline phases formed in various multicomponent water/hydrocarbon/surfactant/alcohol systems with varying compositions and temperatures, have been described in numerous publications [14-22,78,79,84-88]. These studies provide a detailed analysis of the phase equilibria under various conditions and cover all kinds of systems with all levels of disperse phase concentration. Special attention is devoted to the role of low and ultralow values of the surface energy at the interfaces. The author s first observations of areas of stable microheterogeneity in two-, three-, and four-component systems were documented in [66-68],... 

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