Osmotic pressure surface tension

FIGURE 2.8 The effect of micelle formation on some solution properties, (a) Schematic picture of micelle formation, (b) Osmotic pressure, surface tension, and turbidity of solutions of sodium dodecyl sulfate (SDS) as a function of concentration (approximate). CMC = critical micellization concentration. 

Figure 2 summarizes the effect of NaCl concentration, oil chain length and surfactant concentration on the interfacial tension in this system. It is evident that ultralow interfacial tension minimum occurs at a specific salinity or specific oil chain length or specific surfactant concentration. Using light scattering, osmotic pressure, surface tension, dye solubilization and various other techniques, we have shown that the ultralow inter facial tension minimum in this system correlates with the onset of micellization in the aqueous phase and the partition coefficient of surfactant near unity (14). Baviere (15) has also shown that the partition coefficient is near unity at the salinity where minimum interfacial tension occurs. 

Enthalpy, entropy, vapor pressure SolubUity, osmotic pressure Surface tension Viscosity, rheology Condensation form at room conditions Polymorphic crystalline forms Hardness, mechanical strength Roiling and melting temperature... 

Since capillary tubing is involved in osmotic experiments, there are several points pertaining to this feature that should be noted. First, tubes that are carefully matched in diameter should be used so that no correction for surface tension effects need be considered. Next it should be appreciated that an equilibrium osmotic pressure can develop in a capillary tube with a minimum flow of solvent, and therefore the measured value of II applies to the solution as prepared. The pressure, of course, is independent of the cross-sectional area of the liquid column, but if too much solvent transfer were involved, then the effects of dilution would also have to be considered. Now let us examine the practical units that are used to express the concentration of solutions in these experiments. 

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

It can now be used for the extremely important purpose of calculating calcium sulphate and 4,000 dyne/cm. for barium sulphate. These figures entirely confirm the conclusion to which we have come on general grounds, that the surface tensions of solids must have high values. The applicability of the Ostwald-Hulett formula is limited, since it is based on Van t Hoff s equation for osmotic pressure, which only holds for small concentrations and, therefore, in the present case, for low solubilities. 

The attempt to show that surface tension phenomena were the cause of osmotic pressure was first made by Jager, and his theories were vigorously supported and developed by Traube, whose conclusions we shall state and examine briefly. He finds that the more a dissolved substance reduces the surface tension of water the greater is the velocity of osmosis of the solution. Hence he concludes that it is the difference in the surface tensions of solvent and solution which determines the direction and velocity of osmosis. The direction of flow Traube obtains by the following consideration let M (Fig. 7) be a membrane separating two liquids A and B. The molecules of each liquid are then drawn into its interior by the cohesion or intrinsic pressure. If the intrinsic... 

In the case of pure liquids the surface phase is naturally of the same composition as the hulk phase for solutions on the other hand the composition of the surface phase need not necessarily be identical with that of the underlying solution. In general the addition of a solute to a solvent will affect the surface tension of the latter and since the energy of the system strives towards a minimum there will be a tendency if the solute lowers the surface tension of the solvent for the former to accumulate at the surface. If the solute elevates the surface tension of the solvent the reverse action occurs and the surface phase will be poorer in solute than the bulk phase. This enrichment or impoverishment of the surface phase does not continue indefinitely, for a point is reached when the action is balanced by the return from the enriched to the impoverished phase due to diffusion, the rate of which is proportional to the difference in osmotic pressures of the solute in the two... 

In this section, we present a few examples of instruments available for visual observation and imaging of colloids and surfaces, for measurement of sizes and for surface force measurements. Such a presentation can hardly be comprehensive in fact, that is not our purpose here. Throughout the book, we discuss numerous other techniques such as osmotic pressure measurements, light and other radiation scattering techniques, surface tension measurements,... 

In neutral gels, in contrast, neither a nor T0 depend on the shape of samples at all, as shown in Fig. 11. Thus, it is certain that the unusual shape-dependent properties shown in Figs. 9 and 10 are due to ions contained in gels. Although the mechanism underlying the shape dependence is not dear at present, one possible mechanism has been proposed [31] on the basis of the surface tension of ionized gels. Denoting the surface tension as y and the radius of curvature of the gel surface as p, an additional contribution to the osmotic pressure due to... 

Solutions of highly surface-active materials exhibit unusual physical properties. In dilute solution the surfactant acts as a normal solute (and in the case of ionic surfactants, normal electrolyte behaviour is observed). At fairly well defined concentrations, however, abrupt changes in several physical properties, such as osmotic pressure, turbidity, electrical conductance and surface tension, take place (see Figure 4.13). The rate at which osmotic pressure increases with concentration becomes abnormally low and the rate of increase of turbidity with concentration is much enhanced, which suggests that considerable association is taking place. The conductance of ionic surfactant solutions, however, remains relatively high, which shows that ionic dissociation is still in force. 

Bioaccumulation All classes of surfactant are active surface tension depressants. At the critical micelle concentration (CMC) abrupt changes occur in the characteristic properties of surfactants such that surface and interfacial tensions in an aqueous system are at their minimum while osmotic pressure and surface detergent properties are significantly increased. The CMC for most surfactants is reached around 0.01% (18, 19). These effects have an impact on the potential for bioaccumulation of the pesticide, and in the organisms monitored the presence of Dowanol and nonylphenol increased the accumulation of fenitrothion and aminocarb at least 20-300% respectively, over the accumulation obtained in their absence (20). In effect, these adjuvants... 

A number of experimental techniques by measurements of physical properties (interfacial tension, surface tension, osmotic pressure, conductivity, density change) applicable in aqueous systems suffer frequently from insufficient sensitivity at low CMC values in hydrocarbon solvents. Some surfactants in hydrocarbon solvents do not give an identifiable CMC the conventional properties of the hydrocarbon solvent solutions of surfactant compounds can be interpreted as a continuous aggregation from which the apparent aggregation number can be calculated. Other, quite successful, techniques (light scattering, solubilization, fluorescence indicator) were applied to a number of CMCs, e.g., alkylammonium salts, carboxylates, sulfonates and sodium bis(2-ethylhexyl)succinate (AOT) in hydrocarbon solvents, see Table 3.1 (Eicke, 1980 Kertes, 1977 Kertes and Gutman, 1976 Luisi and Straub, 1984 Preston, 1948). 

The physical properties of surface active agents differ from those of smaller or nonamphipathic molecules in one major aspect, namely, the abrupt changes in their properties above a critical concentration. This is illustrated in Fig. 1, in which a number of physical properties (surface tension, osmotic pressure, turbidity, solubilization, magnetic resonance, conductivity, and self-diffusion) are plotted as a function of concentration. All these properties (interfacial and bulk) show an abrupt change at a particular concentration, which is consistent with the fact that above this concentration, surface active ions or molecules in solution associate to form larger units. These association units are called micelles and the concentration at which this association phenomenon occurs is known as the critical micelle concentration (cmc). 

In dilute aqueous solutions, surfactants have normal electrolyte or solute characteristics and are formed at the interface. As the surfactant concentration increases beyond the well-defined concentrations (i.e., critical micelle concentration, c.m.c.), the surfactant molecules become more organized aggregates and form micelles. At the c.m.c., the physicochemical characteristics of the system (osmotic pressure, turbidity, surface tension, and electrical conductivity) are suddenly changed, as shown in Figure 4.19. 

Heat capacity, molar Heat capacity at constant pressure Heat capacity at constant volume Helmholtz energy Internal energy Isothermal compressibility Joule-Thomson coefficient Pressure, osmotic Pressure coefficient Specific heat capacity Surface tension Temperature Celsius... 

---