Interface tension

For the solid-liquid system changes of the state of interface on formation of surfactant adsorption layers are of special importance with respect to application aspects. When a liquid is in contact with a solid and surfactant is added, the solid-liquid interface tension will be reduced by the formation of a new solid-liquid interface created by adsorption of surfactant. This influences the wetting as demonstrated by the change of the contact angle between the liquid and the solid surface. The equilibrium at the three-phase contact solid-liquid-air or oil is described by the Young equation ... 

Besides the spontaneous, complete wetting for some areas of application, e.g., washing and dishwashing, the rewetting of a hydrophobic component on a solid surface by an aqueous surfactant solution is of great importance. The oil film is thereby compressed to droplets which are released from the surface. Hydrophobic components on low-energy surfaces (e.g., most plastics) are only re wetted under critical conditions. For a complete re wetting of a hydrophobic oil on polytetrafluoroethylene (PTFE) by an aqueous solution, the aqueous solution-oil interface tension must be less than the PTFE-oil interface tension... 

SPONTANEOUS OSCILLATION OF ELECTRICAL POTENTIAL AND INTERFACE TENSION IN AN OIL-WATER-SURFACTANT SYSTEM... 

Based on the above results and discussion, the mechanism for the rhythmic oscillations at the oil/water interface with surfactant and alcohol molecules may be explained in the following way [3,47,48] with reference to Table 1. As the first step, surfactant and alcohol molecules diffuse from the bulk aqueous phase to the interface. The surfactant and alcohol molecules near the interface tend to form a monolayer. When the concentration of the surfactant together with the alcohol reaches an upper critical value, the surfactant molecules are abruptly transferred to the organic phase with the formation of inverted micelles or inverted microemulsions. This step should be associated with the transfer of alcohol from the interface to the organic phase. Thus, when the concentration of the surfactant at the interface decreases below the lower critical value, accumulation of the surfactant begins and the cycle is repeated. Rhythmic changes in the electrical potential and the interface tension are thus generated. 

To calculate the force created by this concentration gradient we must relate a difference in concentration to the interfacial tension (y) difference at each end on the Au segment. First, we note that the interfacial tension of a solution may be taken as the mol fraction-weighted average of the component interface tensions (Eq. (4))... 

The author would like to thank Ms. M. Debra Davis for making the surface and interface tension measurements and Dr. K. Lee Matheson for the detergency data. In addition, the author... 

Flow near the interface that is influenced by gradients of interface tension is called Marangoni convection. It may have further modes [27]. Thus, a low Marangoni convection in an interface, which results from small concentration differences, may be increased to a strong flow in the shape of rolling cells by mass transfer. These rolling cells transport liquid out of the... 

Clear test mixtures are used for laboratory experiments to be able to use fully defined, reproducible liquid systems. Such mixtures, according to agreement of the European Federation of Chemical Engineering [35], are listed in Table 9.2. They differ mainly in the interface tension. Compared with these, the variety of technical systems is very high [36]. To guarantee reliable dimensions for equipment, engineers must supplement their ealeu-lations by experiments that include the following ... 

All interface tensions are defined as positive and we consider yijw > yiinv in order to intentionally account for anisotropy. This favours 2D growth but does not prioritize the Frank-van der Merwe mechanism over the others. In fact growth is always 2D, as indicated by the BCF model, but depends on the lateral size of the terraces. Small terraces necessarily imply 3D growth. 

Kxnv Nucleus edge-vapour interface tension... 

The density of the perfluorocarbons is usually more than twice that of their hydrocarbon counterparts. The low dielectric constants, surface/interface tensions and refractive indices of perfluorocarbons reflect their nonpolar character as liquids and solvents.6... 

In a foregoing section, we mentioned that field forces (e,g., of the electric or elastic field) can cause an interface to move. If they are large enough so that inherent counterforces (such as interface tension or friction) do not bring the boundary to a stop, the interface motion would continue and eventually become uniform. In this section, however, we are primarily concerned with boundary motions caused by chemical potential changes. From irreversible thermodynamics, we know that the dissipated Gibbs energy of the discontinuous system is T-ab, where crb here is the entropy production (see Section 4.2). Since dG/dV = dG/dV = crb- T/ A < ), we have with Eqn. (4.8) at the boundary b... 

Curvature relates to the local change in interface area when an interface moves. The energy change per unit volume swept out by the interface is equal to the product of k and the interfacial energy per unit area 7. Normally, for fluids, 7 is independent of the interface inclination h in this case, the interface is isotropic. For example, a soap bubble has isotropic interface tension. If perturbed, a floating individual soap bubble will quickly re-establish its equilibrium form—a sphere of fixed volume. Such a soap bubble will also shrink slowly—the gas will diffuse out of the bubble because of a pressure difference across the soap film (AP = jk = /Rc). Thus,... 

Accordingly, on a surface with a medium hydrophobic property, the interface boundary of oil and water mixture, for instance, will contact the wall surface forming a point between the interface and the surface. The relation between the surface tension and the two liquids can be expressed by Young s equation where y0ii-Water is the interface tension between oil and water, while Yofl-surface/Ywater-surface is the surface tension between the channel walls and the two phases [202]... 

In some instances, it has been observed that the addition of electrolyte and sugars into water increases the interface tension. The adsorbed surfactants migrate away from the interface into the bulk phase (i.e., negative adsorption). 

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