Phase volume ratio

Phase Volume Ratio As the volume of the dispersed phase in a macroemulsion increases, the interfacial film expands further and further to surround the droplets of dispersed material, and the basic instability of the system increases. As the volume of the dispersed phase increased beyond that of the continuous phase, the type of emulsion (O/W) or (W/O) becomes basically more and more unstable relative to the other type of emulsion, since the area of the interface that is now enclosing the dispersed phase is larger than that which would be needed to enclose the continuous phase. It often happens, therefore, that the emulsion inverts as more 

A quantitative expression for the rate of coalescence of droplets in a macroemulsion, which includes most of the factors discussed previously, was developed by Davies and Rideal (1963), based on the von Smoluchowski (1916) theory of the coagulation of colloids. 

The rate of diffusion-controlled coalescence of spherical particles in a disperse system as a result of collisions has been shown by von Smoluchowski to be proportional to the collision radius of the particles, the diffusion coefficient, and the square of the concentration of the particles  

This assumes that every collision is effective in decreasing the number of particles. In the presence of an energy barrier to coalescence E, which is present in all dispersed systems, 

A plot of 1 /n versus t (n is determined by counting the particles per unit volume of the emulsion under a microscope) then permits the evaluation of E, since the slope of the curve equals 

---

The ratio of Eq. (8.66) to Eq. (8.67) gives the ratio of the concentrations of n-mers in phases P and Q f p/f g = Re ". Taking this ratio to be unity for n = 200 gives Re (200) = which is readily solved for A using the R values given. Once these A values are obtained, f p/f g can be evaluated for the required n values. For the phase volume ratios under consideration, the corresponding values of A are listed below also tabulated are the ratios f p/f g for the various n s ... 

However, as stated above, the partition coefficients measured by the shake-flask method or by potenhometric titration can be influenced by the potenhal difference between the two phases, and are therefore apparent values which depend on the experimental condihons (phase volume ratio, nature and concentrahons of all ions in the solutions). In particular, it has been shown that the difference between the apparent and the standard log Pi depends on the phase volume raho and that this relationship itself depends on the lipophilicity of the ion [80]. In theory, the most relevant case for in vivo extrapolation is when V /V 1 as it corresponds to the phase ratio encountered by a drug as it distributes within the body. The measurement of apparent log Pi values does not allow to differentiate between ion-pairing effect and partihoning of the ions due to the Galvani potential difference, and it has been shown that the apparent lipophilicity of a number of quaternary ion drugs is not due to ion-pair partitioning as inihally thought [80]. 

When both the neutral and the n different charged forms of a compound partition into the organic phase, a minimum of n + 1) titrations with different phase volume ratios is necessary to determine the partition coefficient of each species. For a monoprotic substance, for instance, can be related to pK by an empirical equation [119] ... 

Maljkovic, D. Lenhard, Z. The effect of organophosphoric extractant concentration and initial phase volume ratio on cobalt(II) and nickel(II) extraction. International Solvent Extraction Conference, Cape Town, South Africa, Mar. 17-21, 2002, 982-987. 

FIG U RE 1.37 Effects of extraction time and fiber length on two-phase LPME of mirtazapine stereoisomers.156 Influence of extraction time (A) and acceptor-to-donor phases volume ratio (B) on the efficiency of LPME. Plots for the (+)-(5)-mirtazapine (white bars) and (-)-(R)-mirtazapine (black bars) enantiomers (response in area counts). Extraction conditions (A) 1 mL plasma sample 0.1 mL 10 M NaOH 3.0 ml deionized water 7.0 cm fiber length 22 /rL toluene (B) 30 min of extraction 1 mL plasma sample 0.1 mL 10 M NaOH 3.0 mL deionized water toluene. (Reproduced with permission from Elsevier.)... 

Ozone is a powerful though relatively unselective oxidant which is being considered in several pulp mills as a replacement for chlorine in bleaching chemical pulp. The first installation of ozone bleaching equipment was in 1992. The ozone required for a large pulp mill is about 10 ton/day 03 for a 1000 t/day pulp [129]. The phase volume ratio (gas/pulp) of about 8 wt% ozone by corona... 

LLE can be performed simply using separatory funnels. The partition coefficient should therefore be large because there is a practical limit to the phase-volume ratio and the number of extractions. When the partition coefficient is... 

If the phase volume ratio = VJ Va, then the fraction extracted, Ex, is given by ... 

Note The Organic Phase is 10 moldm"" . Calixarene in CHCI3. Aqueous Phase is 2 x 10 moldm U02(CH3C00)2 Buffered to pH 5.9 by 10 moldm acetate. Phase Volume Ratio Org/Aq=0.2. 

This phenomenon can be exploited for separation and concentration of solutes. If one solute has certain affinity for the micellar entity in solution then, by altering the conditions of the solution to ensure separation of the micellar solution into two phases, it is possible to separate and concentrate the solute in the surfactant-rich phase. This technique is known as cloud point extraction (CPE) or micelle-mediated extraction (ME). The ratio of the concentrations of the solute in the surfactant-rich phase to that in the dilute phase can exceed 500 with phase volume ratios exceeding 20, which indicates the high efficiency of this technique. Moreover, the surfactant-rich phase is compatible with the micellar and aqueous-organic mobile phases in liquid chromatography and thus facilitates the determination of chemical species by different analytical methods [104]. 

The effects of many other factors, such as interfacial tension, stirring rate, phase volume ratio or temperature, in aqueous-organic two-liquid-phase media on the stability of biotransformation have been studied [36, 37]. 

Other researchers have also observed an increase in HIPE viscosity with increasing phase volume ratio [77] however, the effects of droplet size, polydis-persity or continuous phase viscosity were not investigated. Further studies [78] revealed that the viscosity increased for smaller mean droplet radii this effect was found to be greater at higher internal phase ratios. The total interfacial area increases as droplet size decreases, so viscosity also increases as more energy is required to deform the larger network of thin films [79]. 

Bibette has used this method to study the effect of osmotic pressure on the stability of thin films in concentrated o/w emulsions [96], by means of an osmotic stress technique. The emulsion is contained in a dialysis bag, which is immersed in an aqueous solution of surfactant and dextran, a water-soluble polymer. The bag is permeable to water and surfactant, but impermeable to oil and polymer. The presence of the polymer causes water to be drawn out of the emulsion, increasing the phase volume ratio and the deformation of the dispersed droplets (Fig. 10). 

It is possible to increase the extent of extraction with a given Kd by increasing the phase/volume ratio. When performing micro-LLE, the analyst works with an extreme ratio of extracting solvent/extracted liquid (for example, 1/800). Another way is to carry out a second and a third extraction. After n extractions the final concentration of the compound in the aqueous phase is... 

The critical concentration was obtained from measurements of the phase-volume ratio of coexisting phases near the critical temperature. At an over-all concentration of 8.5 wt % this ratio was unity. According to the lever rule this concentration is the critical one. 

To produce w/o emulsions the aqueous phase had to be added to the rubber solution. The reverse order of addition yielded o/w emulsions at a phase volume ratio w o of 1 1 it was impossible to change an o/w emulsion into a w/o emulsion even when good w/o emulsifiers, which displayed only a moderate tendency to produce o/w emulsions, were used. The tendency to form w/o emulsions and the stability of these emulsions increased with the following factors (the tendency to form o/w emulsions decreased) ... 

---