Disperse front

Figure 8 shows the microemulsion interface positions for the PDM system in this regime. Convection is not indicated. The dispersion front boundaries were very irregular in shape, and, therefore, those positions are not plotted. However, estimates of the relative dispersion front velocity in each experiment are given in the first two entries of Table III. As is evident from the small difference between these values and those for the brine interface, the brine layer grew very slowly at these salinities. 

The formation of a dispersion front can be described in terms of the diffusion path. As oil diffuses into the liquid crystal dispersion, the continuous phase gradually increases in oil content from an initial composition which would ordinarily be called a micellar solution to compositions which would be called... 

The ratio of the relative diffusion constants of brine and oil in the microemulsion phase was found to be very important. Figure 19 shows the effect of varying this ratio. When oil diffusion is less than that of brine, as would be expected in an oil-in-water microemulsion, the fraction of liquid crystal at the dispersion front Increases over that in the bulk dispersion. This situation corresponds to diffusion path 1 in Figure 19. Essentially, brine diffuses out of the dispersion faster than oil can diffuse in, causing a decrease in overall brine concentration at the interface and hence the formation of additional liquid crystal, the phase having the lower brine content. As mentioned previously, this buildup of liquid crystal was observed experimentally. 

For anti-Langmuir-type (concave) isotherms Eq. 6.49 without i]n, prevails because in this case the disperse front originates from the front of the injection pulse. 

Analysis of disperse fronts ECP (elution by characteristic point) FACP (frontal analysis by characteristic point) Pulse or step injection (high concentration) Slope of dispersive front Single component Small sample amounts Highly efficient columns and small plant effects necessary Phase equilibrium is required (sensitive to kinetics) Precise detector calibration necessary... 

Proportional pattern or disperse front— usually a gradual and asymmetric transition during regeneration or uptake under unfavorable (Type II) equilibrium. The physical limit (without mass transfer effects) is a simple wave. 

Analysis of disperse fronts elution by characteristic point (ECP), frontal analysis by characteristic point (FACP)... 

Slope of dispersive front Highly efficient columns and small plant effects necessary Phase equilibrium is required (sensitive to kinetics) Precise detector calibration necessary... 

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