Interface-stabilized phases

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

R.F. Sekerka. Application of the time-dependent theory of interface stability to an isothermal phase transformation. J. Chem. Phys. Solids, 28(6) 983—994, 1967. 

An explanation of why convection occurred when brine formed in the TRS system can be given by interface stability analysis (18). During the experiments, slight tipping of the sample cells indicated that the intermediate brine phases were more dense than the mixtures of liquid crystal and brine below them. This adverse density difference caused a gravitational instability for which the smallest unstable wavelength X is given by... 

Clearly the film thickness, fluid density, and perhaps the orientation of the surfaces [207] are additional thermodynamic variables that may shift or alter phase boundaries. Cases where a single interface stabilizes a different phase than the bulk are central to the field of wetting. The presence of two interfaces separated by only a few nanometers leads to more pervasive phase changes. 

In some applications, the stability of the phase-arrangement is increased by additional surfactants as the third phase, stabilizing the plug interface (three-phase liquid-liquid) [144]. An external pressure is applied for the transport of the plugs. A comprehensive general discussion of the platform can also be found in recent review papers [30, 145, 146]. 

In correspondence with the detrimental role that interfacial phenomena play in the formation and stability of disperse systems, the book starts with the description of phenomena at interfaces separating phases that differ by their phase state (Chapters I-III). Then the formation (Chapter IV), properties (Chapters V-VI), and stability (Chapters VII-VIII) of disperse systems are covered. The last chapter (Chapter IX) in the book is devoted to the principles of physical-chemical mechanics, the part of colloid science in the development of which the scientific school established by Rehbinder and Shchukin played the leading role. 

Moreover, the transfer of surfactant between the liquid phases can also have an impact on the interface stability. In fact it has been shown (170, 171) that, depending on the ratio between the diffusion coefficients in the two phases, the transfer of matter across the interface can give rise to interfacial instabilities. 

STABILITY OF MOVING INTERFACES WITH PHASE TRANSFORMATION... 

It is possible to modify the interfaces between liquids with specific additives. This was discovered by andent and medieval investigators and applied in the form of soaps, and later in food technology and in the application of dyes. The mechanisms of these additives only came to be realized in about 1900. Such additives are generally molecules with hydrophobic and hydrophilic sedions that align along interfaces between the two liquid phases. They reduce interfadal tension and stabilize phase morphology to smaller dispersed phase sites. This phenomenon was realized by IG Farbenindustrie chemists who applied it in the late 1920s in emulsion polymerization that they used to produce synthetic rubber. 

A well-accepted definition of nanocomposite material is that one of the phases has dimensions in the order of nanometers [51]. Roy et al. [52] present in their paper on alternative perspectives on nanocomposites a summary of features of particle properties when particle size decreases beyond a critical size. As dimensions reach nanoranges, interactions improve dramatically at the interfaces of phases, as do the effect of surface area/volume on the structure-property relationship of the material [53]. There is definite increase in the modulus of the material reinforced with composites, higher dimensional stability to thermal treatment, as well as enhanced barrier, membrane (conductive properties) and flame resistance. Thus, as Paul and Robeson [54] rightly put it, the synergistic advantage of nanoscale dimensions ( nano effect ) relative to larger-scale modifications is an important consideration ... 

In the liquid ion-exchanger electrodes of Corning, a ceramic frit imbedded in the electrode body serves as an interface-stabilizer. As shown in Fig. 28, the inner shunt electrode, with its own electrolyte, dips directly into the exchanger phase. 

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