Surface tension concentration dependence

Therefore, we have established once again that the linear dependence of the adsorption on concentration corresponds to the initial linear region in the surface tension - concentration dependence (see Fig. (II-7)). Since b is constant within the homologous series, it is the value of constant A that determines the steepness of the adsorption increase with increasing concentration. For this reason constant A is referred to as the adsorption activity. By comparing eqs. (II. 19) and (11.20) one establishes that A is related to the work of adsorption, p0 - p(0s), as... 

The highest limiting value of the adsorption corresponds to the logarithmic region in the surface tension - concentration dependence. This... 

What characterizes surfactants is their ability to adsorb onto surfaces and to modify the surface properties. At the gas/liquid interface this leads to a reduction in surface tension. Fig. 4.1 shows the dependence of surface tension on the concentration for different surfactant types [39]. It is obvious from this figure that the nonionic surfactants have a lower surface tension for the same alkyl chain length and concentration than the ionic surfactants. The second effect which can be seen from Fig. 4.1 is the discontinuity of the surface tension-concentration curves with a constant value for the surface tension above this point. The breakpoint of the curves can be correlated to the critical micelle concentration (cmc) above which the formation of micellar aggregates can be observed in the bulk phase. These micelles are characteristic for the ability of surfactants to solubilize hydrophobic substances in aqueous solution. So the concentration of surfactant in the washing liquor has at least to be right above the cmc. 

Surfactants and block polymers useful for lowering the surface tension of solutions have two components the hydrophobe, which has a lower surface tension and is usually insoluble in aqueous solutions, and the hydrophile, which is the more compatible component. The lowering of surface tensions of solutions provides evidence of the degree of surface activity of the hydrophobe but is a less reliable way of inferring surface activity compared with direct surface tension measurement of the hydrophobic material, because surface tension lowering depends also on the concentration of surfactant used, the type and relative proportions of hydrophobe and hydrophile, the overall molecular weight of the surfactant, and the solvent used. Nevertheless, even the best surfactant of a given class cannot perform beyond certain limits, and these limits offer a useful measure of surface activity. 

Since surface tension reduction depends on the replacement of solvent molecules at the interface by surfactant molecules, the efficiency of a surfactant in reducing the surface tension should reflect the concentration of the surfactant at the interface (Cg) relative to that of the bulk liquid phase (Cb). Generally, when the surface tension is reduced to 20 dynes/cm, the surfactant adsorption at the interface is close to its maximum. Adsorption at... 

The decrease in the surface tension at constant adsorption, occurring in agreement with the Gibbs equation, is solely due to the increase in chemical potential of the adsorbed substance caused by the increased concentration of the latter in solution. As is commonly known, the increase in the chemical potential in a stable two-component system always corresponds to the concentration increase. For the present case it translates into the increase of surface concentration, and consequently, of the adsorption. Therefore, in the concentration region where the surface tension linearly depends on the log of concentration, a slow but finite, increase in adsorption not detected experimentally should occur. At the same time a sharp increase in the chemical potential of the surfactant molecules in the adsorption layer... 

The condensate that collects on the cold surface is usually a completely homogeneous, or miscible, mixture of components. In general, the relative composition of the liquid components in the condensate is different from the composition in the vapor phase (except for an azeotropic mixture, where the condensate has the same exact molar concentration ratio as the vapor phase) [194]. The film that forms is not necessarily smooth but may show the appearance of streamers (or rivulets), waves, or droplets, depending on the particular mixture and its surface tension (which depends on the local wall temperature) [25,195,196]. If the condensate mixture is heterogeneous, or immiscible (as can occur when one component, for example, is aqueous and the other is organic), the pattern can be quite complex, looking somewhat like dropwise condensation [25,193,197]. These different condensate patterns affect the resulting fluid flow and heat transfer. 

As we have shown, the surface forces at an interface depend upon the surface tension gradients there. If adsorbed surface-active materials are distributed at an interface, then this distribution must be known to determine the surface forces, since the surface tension gradients depend on the local surface concentration of adsorbed material. The surface mass concentration of the adsorbed substance follows from an interfacial mass balance. 

Abstract Experimental results are presented for the counterion dependence of the adsorption of alkali decyl sulfates (Li+, Na+, K+, Rb+ and Cs" ) at the air/solution interface. The experimental adsorption isotherms calculated from equilibrium surface tension/concentration data by means of the Gibbs equation... 

A new method is proposed for the preparation of surface chemically pure surfactant solutions. Experimental results are presented for the counterion dependence of the adsorption of alkali decyl sulfates at the air/solution interface. The experimental adsorption isotherms calculated from equilibrium surface tension-concentration data show significant counterion dependence. While the adsorption isotherms of potassium decyl sulfate, rubidium decyl sulfate and cesium decyl sulfate fall into the same group, the surface activity of sodium decyl sulfate and lithium decyl sulfate is significantly smaller. The adsorption isotherms do not correspond to the Langmuir isotherm because there is a pronounced change in the shape of the isotherms at around 2-2.5x10 mol/cm surfoce excess. 

During the movement of gas bubbles, the oil film is collected at the production well located outside the reservoir. As the bubble travels down the capillary, the flow in the surrounding fluid causes a nonuniform distribution of surfactant on the bubble surface. This nonuniform surfactant distribution determines the surface forces, since the surface tension gradient depends on the local surface concentration of the adsorbed material. The film thickness and the total pressure drop to drive the bubble are dependent on the surfactant distribution. This kind of flow is known as diffusocapillary flow. The surfactant is swept toward the rear of the bubble where it accumulates. 

The time required for surface tension reduction depends on diffusion processes involved in surfactant adsorption. Kinetic models for surfactant adsorption divide the adsorption process into two steps [67]. The first step is the transport of the surfactant to the subsurface, driven by a concentration gradient or hydrody-... 

The lowest surface tensions, 7min, the coiTesponding concentrations for the surfactants (HFPO)2 6C6H5, and their cmc values are given in Table 4.16. The surface tension of xylene (28.6 mN/m) was lowered considerably even at small surfactant concentrations. The surface tension decrease depends on the length of the perfluorinated chain, exhibiting a maximum decrease at n = 5, However, Abe et... 

Because the reaction takes place in the Hquid, the amount of Hquid held in the contacting vessel is important, as are the Hquid physical properties such as viscosity, density, and surface tension. These properties affect gas bubble size and therefore phase boundary area and diffusion properties for rate considerations. Chemically, the oxidation rate is also dependent on the concentration of the anthrahydroquinone, the actual oxygen concentration in the Hquid, and the system temperature (64). The oxidation reaction is also exothermic, releasing the remaining 45% of the heat of formation from the elements. Temperature can be controUed by the various options described under hydrogenation. Added heat release can result from decomposition of hydrogen peroxide or direct reaction of H2O2 and hydroquinone (HQ) at a catalytic site (eq. 19). 

In a foam where the films ate iaterconnected the related time-dependent Marangoni effect is mote relevant. A similar restoring force to expansion results because of transient decreases ia surface concentration (iacteases ia surface tension) caused by the finite rate of surfactant adsorption at the surface. 

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 ... 

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 results were presented in the form of isotherms, in which the properties are plotted versus the concentration. Nevertheless analysis of the isotherms was made based on available melting diagrams approach that the melts consist of TaFg3 and TaF7Cl3 complex ions. However, according to this general conception [312-314], the isotherm of the surface tension must, in such a case, have either a minimum or at least display prominence of the dependence in the direction of the concentration axis. 

In Fig. 24 the dependence of the surface tension on the concentration is shown for two sodium alkanesulfonates which were purified by exploitation of... 

In Fig. 2.58 (Hetsroni et al. 2001b) the dependencies of the surface tension of the various surfactants a divided on the surface tension of water ow are shown. One can see that beginning from some particular value of surfactant concentration (which depends on the kind of surfactant), the value of the relative surface tension almost does not change with further increase in the surfactant concentration. It should be emphasized that the variation of the surface tension as a function of the solution concentration shows the same behavior for anionic, non-ionic, and cationic surfactants at various temperatures. 

For example, for alkyl (8-16) glycoside (Plantacare 818 UP) non-ionic surfactant solution of molecular weight 390 g/mol, an increase in surfactant concentration up to 300 ppm (CMC concentration) leads to a significant decrease in surface tension. In the range 300 < C < 1,200 ppm the surface tension was almost independent of concentration. In all cases an increase in liquid temperature leads to a decrease in surface tension. This surface tension relaxation is a diffusion rate-dependent process, which typically depends on the type of surfactant, its diffusion/absorption kinetics, micellar dynamics, and bulk concentration levels. As the CMC is approached the absorption becomes independent of the bulk concentration, and the surfactant... 

Retention in HIC can be described in terms of the solvophobic theory, in which the change in free energy on protein binding to the stationary phase with the salt concentration in the mobile phase is determined mainly by the contact surface area between the protein and stationary phase and the nature of the salt as measured by its propensity to increase the surface tension of aqueous solutions [331,333-338]. In simple terms the solvopbobic theory predicts that the log u ithn of the capacity factor should be linearly dependent on the surface tension of the mobile phase, which in turn, is a llne2u function of the salt concentration. At sufficiently high salt concentration the electrostatic contribution to retention can be considered constant, and in the absence of specific salt-protein interactions, log k should depend linearly on salt concentration as described by equation (4.21)... 

It was mentioned previously that the narrow range of concentrations in which sudden changes are produced in the physicochemical properties in solutions of surfactants is known as critical micelle concentration. To determine the value of this parameter the change in one of these properties can be used so normally electrical conductivity, surface tension, or refraction index can be measured. Numerous cmc values have been published, most of them for surfactants that contain hydrocarbon chains of between 10 and 16 carbon atoms [1, 3, 7], The value of the cmc depends on several factors such as the length of the surfactant chain, the presence of electrolytes, temperature, and pressure [7, 14], Some of these values of cmc are shown in Table 2. 

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