Stratification phenomenon

Electrodecantation is a stratification phenomenon that may take place when colloidal dispersions are subjected to an electric field between vertical membranes permeable to ions but not to colloids. This phenomenon was first observed in 1923 by W. Pauli of Austria (Ref 21)... 

A stratification phenomenon in foam films from sodium oleate aqueous solutions has been described by Johonnott [314] and Perrin [318] in the beginning of the century. The stepwise thinning has been studied by many authors [e.g. 235,345], It became evident that this phenomenon is universal and has been observed also in emulsion films [346,347], asymmetric films of the air-water/oil type [348], films from latex suspensions [349] and liquid crystalline films [350],... 

Regardless of the numerous studies of stratified films the phenomemon lacks complete quantitative explanation. However, this does not mean that progress in its understanding during the last years has not been achieved. The review of Langevin and Sonin [35] reveals the contemporary state of the problem and considers the stratification phenomenon in films from micellar solutions and films from surfactant lamellar phases. 

The stratification phenomenon is connected with the layered ordering of molecules or micelles inside the film. During drainage these ordered layers of molecules or micelles flow out towards films periphery, i.e. towards the meniscus that surrounds the film. It is clear that during thinning, the film thickness will decrease until the final state is reached. 

Thin liquid films made from the mixed solutions below CAC exhibit a stratification phenomenon, with a stratum thickness corresponding to the mesh size of the polymeric network, i.e. the distance between overlap points of two polymer chains. The oscillatory forces are particular to polyelectrolytes and disappear when the electrostatic forces are screened with salt. The study of freely suspended films gives new useful insights into the structure of semidilute polymer solutions which are presently the object of numerous speculations. 

Effects of Micellar Concentration and Size- The effect of important technological parameters on the film stratification phenomenon is discussed next. 

Lobo and Wasan (81) observed the drainage and stability of pseudoemulsion films from nonionic surfactant solutions (Enordet AE1215-30 ethoxylated alcohol) at concentrations much above the CMC. They observed that, for a 4 wt% surfactant system, the film thinned stepwise by stratification (Figure 27), in a fashion similar to the foam films from micellar solutions (Figure 14). Three thickness transitions were observed (81) at 4 wt% concentration with n-octane as oil, which was the same number of steps as observed by Nikolov et al. (54) in foam films at the same concentration. This observation on the micellar layering in the pseudoemulsion film confirms, again, the universality of the stratification phenomenon. 

The liquid-hydrogen stratification test program described in this paper was undertaken to overcome the deficiencies previously experienced, to provide data from a larger-size test vessel, and to investigate the effects of liquid oscillation and sloshing on the stratification phenomenon. The results of the program are described in detail in a final report to NASA [ ]. 

With reference to Fig, 1, two basic equations describing the stratification phenomenon may be derived i.e.,... 

Another information system was installed on the surge line and database was created for real time monitoring of pipe metal temperature to evaluate the possible effect of the fluid stratification. It was proven that the stratification phenomenon does not create unacceptable stresses on the pipe metal. 

In fact, the blast contribution from the liquid will be affected by the lack of homogeneity in liquid temperature, decreasing as liquid temperature stratification increases (since liquid stratification reduces the average liquid temperature, the vaporization fraction will decrease). However, the actual knowledge of the liquid stratification phenomenon does not allow the suitable correction to be introduced into tiie blast calculation. 

It was found that in each case the foam stability was effected by a completely different mechanism. In the first case, where the foam film containing oil is solubilized within the micelle to form a microemulsion, the normal micellar interactions are changed. It had been earlier demonstrated that micellar structuring causes stepwise thinning due to layer-by-layer expulsion of micelles and that this effect was found to inhibit drainage and increase the foam stability. Generally, this stratification phenomenon was found to be inhibited by the oil solubilized within the micelle which decreased the micelle volume (representing a decrease in the repulsion between the micelles). 

Additional developments in the SSC-K code include models for reactivity feedback effects for the metallic fuel, and the PSDRS. Also a two dimensional hot pool model has been build into SSC-K for analyzing the thermal stratification phenomenon in the hot pool. The control system model in SSC-K is flexible enough to handle any control system. For code maintenance and readability, SSC-K was converted to FORTRAN 90 free form and the use of standard FORTRAN 90 has enhanced code portability. 

Retrogradation characteristic is a visual finding of starch aging. Starch paste can appear stratification phenomenon after the gelatinized starch places a period of time. The upper transparency increases, but the lower layer transparency decreases. This is the aging characteristic of starch. 

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