Binary solutions, surface tension

Surface tensions for aqueous solutions are more difficult to predict than those for nonaqueous mixtures because of the nonlinear dependence on mole fraction. Small concentrations of the organic material may significantly affect the mixture surface tension value. For many binary organic-water mixtures, the method of Tamura, Kurata, and Odanfi maybe used ... 

It will be observed that the F, N curves for such binary mixtures follow the same course—a rapid followed by a more gentle rise of F as iV increases to a well defined maximum followed by a drop and an asymptotic fall in the F value. In the case of alcohol water mixtures F ax. is obtained at about 0 3A. To find an adequate explanation for the complete F, N curve is by no means an easy matter. It is clear that the first portion of the curve may be taken to represent an increasing surface concentration of alcohol and this proceeds to a limiting value—an observation first made by Milner (Phil. Mag. xill. 96, 1907), who showed that for relatively strong solutions of acetic acid the surface tension of the solutions could be expressed as a function of the concentration of the acetic acid in the following form ... 

In a previous publication ( ), results were presented on the micellar properties of binary mixtures of surfactant solutions consisting of alkyldimethylamine oxide (C12 to Cig alkyl chains) and sodium dodecyl sulfate. It was reported that upon mixing, striking alteration in physical properties was observed, most notably in the viscosity, surface tension, and bulk pH values. These changes were attributed to 1) formation of elongated structures, 2) protonation of amine oxide molecules, and 3) adsorption of hydronium ions on the mixed micelle surface. In addition, possible solubilisation of a less soluble 1 1 complex, form between the protonated amine oxide and the long chain sulfate was also considered. 

Synergism in surface tension reduction efficiency. The efficiency of surface tension reduction by a surfactant is defined (9) as the solution phase concentration required to produce a given surface tension (reduction). Synergism in this respect is present in a binary mixture of surfactants when a given surface tension (reduction) can be attained at a total mixed surfactant concentration lower than that required of either surfactant by itself. This is illustrated in Figure 2. 

Several other empirical relations for diffusion coefficients have been suggested Olson and Walton (01) have devised a means for estimating diffusion coefficients of organic liquids in water solution from surface-tension measurements. Hill (H5) has proposed a method based on Andrade s theory of liquids which allows for the concentration dependence of the diffusion coefficient in a binary liquid mixture. The formula of Arnold (A2, T6, p. 102) does not seem generally useful inasmuch as it contains two constants ( abnormality factors ) characteristic of the solute and of the solvent. 

The salt effects of potassium bromide and a series office symmetrical tetraalkylammonium bromides on vapor-liquid equilibrium at constant pressure in various ethanol-water mixtures were determined. For these systems, the composition of the binary solvent was held constant while the dependence of the equilibrium vapor composition on salt concentration was investigated these studies were done at various fixed compositions of the mixed solvent. Good agreement with the equation of Furter and Johnson was observed for the salts exhibiting either mainly electrostrictive or mainly hydrophobic behavior however, the correlation was unsatisfactory in the case of the one salt (tetraethylammonium bromide) where these two types of solute-solvent interactions were in close competition. The transition from salting out of the ethanol to salting in, observed as the tetraalkylammonium salt series is ascended, was interpreted in terms of the solute-solvent interactions as related to physical properties of the system components, particularly solubilities and surface tensions. 

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... 

The -maxima and minima on viscosity-composition curves are reminiscent of those on vapour pressure-composition curves of binary, mixtures. 5 The vapour pressures and viscosities are equal at some temperatures, say T and To, and T and To respectively. Then To/T—To7T =C(T —T), where C is a constant. A plot of TojT—To IT against T—T gives a straight line in many cases, both for vapour pressure and viscosity in other cases, the vapour pressure shows a minimum and the viscosity a maximum, and the vapour pressure a maximum and the viscosity a minimum. Prasad, 6 from the relation with vapour pressure deduced the equation rj =rjjrio= +ac, where c=conc. of non-electrolyte. The theoretical value of a is 0 00652 the observed values were glucose 0 44, fructose 0 44, sucrose 0 78, independent of temperature. According to Errera, the curves depend on the electric dipolarity of the liquids if both are nonpolar, the curve is concave to the composition axis whilst if both are polar, it is convex. Wolkowa found that the viscosity of a solution is approximately proportional to its heat of dilution. There seems to be no relation between the viscosity and surface tension of a mixture of acetic acid and water (cf. salt solutions, 13.VIII E). Mixtures of isomorphous substances obey an approximately linear relation. 

Values closer to 2-12 are found if allowance is made for dissociation in calculating M. This would indicate that no change in association is produced by the presence of the electrolyte in the water. The Eotvos constants of binary mixtures seem to depend on the concentration and temperature. The effect of temperature is either (i) normal, when d[a MvY>mdt is about 2-1, or (ii) abnormal, when this coefficient is less than 2-1 ljut increases with temperature from these results, conclusions have been drawn as to the molecular weights of dissolved substances. Light (including ultraviolet) has no influence on the surface tension of solutions. ... 

B. Ya. Telterbaum. Doklady Akad. Nauk S.S.S.R. 71, 705-8 (1950). Surface tension methanol, aniline, H2O in binary solutions. 

The value of (ytan ) for hydrophilic particles 9 < 90°) in (2) is always negative (y>0) and the sign of d9/dA is opposite to the sign of the derivative dU/dA. Since dTL /dA < 0, d9/dA is positive. Because upon compression dA < 0, d9 has to be also negative, i.e. 0 decreases upon compression and the hydrophilic particles are expelled into the aqueous phase. For the hydrophobic particles (90° < 6), 9 increases upon compression and particles are expelled into the upper phase. Thus, a simple solution for the distinction between hydrophilic and hydrophobic particles exists. Upon observation, hydrophilic particles will gradually escape from the monolayer whereas in the opposite case a covered interface will always be observed. 0 at a liquid/gas interface depends via the Young equation on the surface tension y of the liquid. Then, the area shift AS in (1) is also a function of y (If). The stronger the compression of the binary... 

Hi) Surface excess entropies. Basically, from the temperature dependence of the surface tension S" can be derived. For binary mixtures, this is a complicated procedure (sec. 4.2d). However, for dilute solutions it is easier. Equations 4.2.8a and b) for the Gibbs equation now reduce to... 

Since the surface tension is a thermodynamic property, one of the main problems is to define the surface tension of the ideal solution. The first attempt to define the behavior of the ideal solution was made by introducing the simple additivity law based on the molar fraction scale. However, such a behavior was never observed in real systems and several sophisticated attempts were therefore made to describe the composition dependence of surface tension in binary systems with sufficient accuracy taking into account the properties of both the components. Most approaches are based on the substitution of molar fractions by the volume fractions. Such an approach seems not to be quite reliable because of the energetics and not because of the volume character of this quantity. 

Now, we calculate the surface tension of an ideal binary solution from Eq. (6.30). Since the system is in equilibrium, it holds... 

The surface tension of binary mixtures of water + monoethanolamine and water + 2-amino-2-methyl-l-propanol and tertiary mixtures of these amines with water from 25 to 50°C have been reported. = The surface tension of aqueous solutions of diethanolamine and triethanolamine from 25 to 50°C have been analyzed. ... 

Nonlinear dependence of the surface tension on temperature. In the preceding, it was assumed that the dependence of the surface tension on temperature is linear. However, for a number of liquids, such as water solutions of high-molecular alcohols and some binary metallic alloys, it was experimentally proved that the function a = a(T ) is nonlinear and nonmonotone [264, 493, 494], In Figure 5.3, experimental curves are presented [264] showing that a - o(T ) can have a pronounced minimum (the numbers on curves correspond to the number of carbon atoms in the alcohol molecule the experiments were carried out at... 

The derivative of the surface tension with respect to temperature at the interface between condensed phases in binary systems can be either positive, or negative, or even change its sign when the temperature changes, which makes it different from the vapor-liquid interface in a one-component system. Within a certain approximation one may assume that in binary systems, as in single-component ones, the value r = -do/dT is the excess of entropy within the discontinuity surface. Consequently, for the interface between condensed phases, the excess of entropy can not only be positive (as it was with singlecomponent systems), but also negative. This situation is especially typical for the interface between two mutually saturated liquid solutions. 

Role of Adsorbed Surfactant Layer. Foams, irrespective of the nature of liquid and gas involved, require a third component for stabilization of thin films (lamellae) of the liquid. In the familiar case of aqueous soap films, this third component is the soap, a surface-active chemical that adsorbs at the gas—liquid interface and lowers the surface tension of water. The two effects, adsorption at the liquid surface and the depression of surface tension, are intimately linked and occur concomitantly. The adsorption is defined as the excess moles of solute per unit area of the liquid surface. In a binary system, this surface excess can be directly related to the lowering of surface tension by Gibbs adsorption equation ... 

Adsorption at the aqueous-air interface from binary solutions of proteins and surfactants can be conveniently followed by surface tension measurements in which the protein concentration is kept constant and the surfactant concentration is increased to concentrations in excess of the cmc. Studies of this type were first carried out not with proteins but with polyethylene oxide in the presence of SDS [70], and it was found that plots of surface tension as a function of surfactant concentration showed a number of interesting features in comparison with the surface tension concentration plot in the absence of polymer (Fig. 4). Very similar behavior to that first observed for the polyethylene oxide-SDS system has been found for protein-surfactant systems including bovine serum albumin plus SDS [67], gelatin plus SDS [52], and reduced lysozyme plus hexa (oxyethylene) dodecyl... 

To fix our ideas let us consider two infinite, flat, parallel plates in adsorption equilibrium with a binary solution. Suppose that at a separation H and at a given solution concentration the relative adsorption of component 2 is Tf H). We wish to know how the presence of the solution between the plates at a mole fraction x2 affects the surface tension. 

Here F, is the excess number of moles of compound i at the surface and /r, is the chemical potential of the ith component. For an ideal binary solution at constant temperature, the surface composition of the solution can be estimated from the surface tensions of the two components by the equation... 

The miceUization of binary surfactant solutions is studied by the method of tensiometry at the variation of the fraction of ionic surfactant within the range 0-1.0. The quantitative treatment of the surface tension isotherms within the framework of the phase separation modeP showed that the values of the interaction parameter p in these systems lay within the range (-0.85)-(-. 6). This indicates that in these systems synergetic behaviour occurs, i.e. the mixed aggregates are formed. The surface potential is calculated for all the systems. A decrease in the potential is shown to occur with a decrease in In... 

Of all the reagents of the reaction mixture under study, polyo rpro-pylene glycol possesses the highest chemical affinity for KEP-2 and defines the distribution of the latter in the reaction system. The model system of oligoglycol-KEP-2 has been studied to elucidate the structure-forming effect of surfactant. The concentration dependence of the surface tension 7 for the concentration range of siufactant from 0 to 0.3% has been analyzed and isotherms typical of surfactant solutions were obtained (Fig. 2.25). The equation for binary solutions of surfactant was used ... 

MEASUREMENT OF SURFACE TENSION OF NONELECTROLYTE BINARY SOLUTIONS. 

A THEORY OF SURFACE TENSION OF BINARY SOLUTIONS. I. BINARY LIQUID MIXTURES OF ORGANIC COMPOUNDS. 

SURFACE TENSION OF BINARY SOLUTIONS OF NON-ELECTROLYTES. II. CALCULATION FROM THE PROPERTIES OF PURE COMPONENTS. 

---