Particle size distribution emulsions, effect

Quasi-elastic light scattering is an excellent technique for studying the formation and stability of submicrometer emulsions. Improvements in the methods of quasi-elastic light scattering data acquisition and analysis that enable full particle-size distribution studies of sub-micrometer emulsion systems are discussed. Using several oil/water emulsion systems as examples, we demonstrate the ability of these techniques to determine the effect of emulsifier concentration on the particle-size distribution produced by an inversion method of emulsification. Some of the benefits of obtaining the full distribution are also discussed. 

The aim of this paper is to describe the experimental and numerical techniques that, when combined, provide a procedure that enables full particle-size distribution studies of sub-micrometer emulsion systems. We then present distribution results for several oil/water emulsions to demonstrate the ability of these techniques to monitor the effect of processing variables (such as surfactant concentration) on the final emulsion. Finally, we discuss some of the problems of converting the intensity weighted distribution to a mass weighted distribution and suggest methods for minimizing or eliminating some of these problems. 

We hav shown that with the use of a mixed surfactant system in styrene emulsion polymerization, the composition of the mixed surfactant has an effect on the rate of polymerization, the number of particles formed and the particle size distribution. We have also shown that a change in the ratio, r of the two surfactants in the mixture results in a considerable change in the micellar weight of the resultant mixed micelles. We have thus proposed and proven that the efficiency of nucleation of particles (even when the same number of micelles is used in the experiment) is dependent on the size of the mixed micelle, and that there is an optimum size at which the polymerization rate is the fastest and the particle size distribution is the narrowest. 

Sedimentation Techniques. Other techniques that effect a physical separation include gravitational or centrifugal sedimentation, in which particles or emulsion droplets are separated on the basis of size and density. The separation that occurs can be quantified by monitoring X-ray or light absorbance as a function of position. Stokes law then can be used to determine the particle size distribution from the absorbance data as a function of the sedimentation time (73, 74). 

The effect of particle size distribution on the viscosities of suspensions and emulsions has been investigated (28, 32-35). Most of these studies indicate that the effect of particle size distribution is of enormous magnitude... 

The chemical nature and the concentration of an emulsifying agent also play a role in determining the viscosity of emulsions (37). The average particle size, particle size distribution, and the viscosity of the continuous phase (to which an emulsifier is normally added) all depend upon the properties and concentration of emulsifying agent. Also, ionic emulsifiers introduce electroviscous effects, leading to an increase in the emulsion viscosity. 

The oil-in-water emulsions studied in this experiment contained sufficient levels of crystallized fat to lead to droplet destabilization via partial coalescence. The role of intradroplet crystallization and its effects on emulsion stability and partial coalescence were determined by examining the evolution of droplet size distribution [volume weighted particle size distribution as a function of time. All freshly... 

Two crude oils were used, a California crude with a viscosity of 24 poise at 25 C and a Canadian crude of 164 poise. Both could be emulsified by the addition of NaOH which reacted with the acids present in the crude. A series of oil-in-water emulsions containing 60% (by volume) of oil were prepared. Concentration of NaOH and NaCl and mixer speed were varied. Emulsion stability was measured as was particle size distribution and viscosity and the effect of aging on the latter two. Emulsions of the heavier crude had viscosities about 600 times smaller than the crude viscosity. 

The effect of oil viscosity on initial emulsion viscosity is not clear from these experiments. The St. Lina crude is about six times as viscous as the California crude. The apparent viscosity of the lower viscosity St. Lina Crude emulsion (2 x 10 moles NaOH/gram oil) is less than 50% greater than the lowest viscosity moderately stable California crude emulsion (4.0 x 10 NaOH). The average particle size of the St. Lina emulsion is 7 microns while that of the Shell crude emulsion is about 3 microns (see Figure 8). Since particle sizes, particle size distributions and types of oil are different, no conclusions can be drain about the influence of oil viscosity. There is, however one fact which should be emphasized, namely that viscosities 600 times lower than that of the crude were observed for 60% St. Lina crude emulsions. 

It was shown that the basic principle of mini-emulsion polymerization can be extended to the reaction systems stabilized by cationic and non-ionic emulsifiers, leading to a narrow particle size distribution [ 102]. Besides, the effect of the... 

Fundamental mixing studies on simple two-component systems have provided insight into the effect of mixing parameters on critical emulsion properties such as particle size distribution. For example, Nagata [81] has shown the distribution of sizes of the dispersed liquid phase as a function of agitator speeds. As we might expect, a normal distribution occurs at higher speeds. In a similar study, the effect of surface tension was determined for several liquid dispersed phases from benzene to paraffin oil [82],... 

Figure 40.4 shows the SEM images of barium titanate powders synthesized at 850°C. The effect of using various barium concentration and precursor sources for titanium was studied [3] In Fig. 40.4a barium concentration is 0.3 mol/L and titanium source is Ti02 sols, in Fig. 40.4b barium concentration is 0.03 mol/L and the titanium source is the same as above, i.e., Ti02 sols in Fig. 40.4c the barium concentration is 0.3 mol/L the same as Fig. 40.4a, but the titanium source is the TiCl4 precursor. When a high concentration of barium was used (0.3 mol/L), the particles were spherical with diameters of 200-500 nm (Fig. 40.4a), whereas for a low concentration of 0.03 mol/L the particle diameter is from 100 to 200 nm (Fig. 40.4b). Therefore, the particle diameter of the barium titanate may be controlled by the metal ion concentration in the emulsion droplet. Particles in Fig. 40.4c exhibited a broader particle size distribution [3]. The diagram of Fig. 40.2 and the discussion provided later may help interpret the results observed in Figs. 40.3 and 40.4.

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