Emulsion Sauter diameter

The values of these averages can be very different. Typically, the higher the values of n and m are, the larger is the value of the average size. Which one you should use simply depends on the application. When it relates to the surface area (think of emulsion stability, amormt of surfactant needed, energy required to make the emulsion, etc.) then the Sauter diameter is probably the best one. If the application is related to the volume (e.g., amount of oil in the product, material dissolved in the particles), the volume average diameter may be more suitable. 

An emulsion typieaUy eonsists of droplets with many different sizes. The properties of an emulsion strongly depend on the droplet sizes present. There are different average droplet sizes that one ean use the Sauter diameter is often used. Next to the average droplet size, the width of the distribution is important. 

In continuous mechanical emulsification systems based on turbulent flow, the power density Py viz. power dissipated per unit volume of the emulsion) and residence time, L, in the dispersing zone have been found to influence the result of emulsification as measured by the mean droplet size 0(3 2 which is called the Sauter diameter . This dependency is in most cases described by the following expression ... 

The Sauter diameter or mean droplet size is also used to compare the efficiency of emulsification process. Comparisons are based on emulsion stability small diameter corresponds to a stable emulsion. 

In another study conducted at irradiation power values of 32, 25 and 17 W, reducing the sonication power from 32 to 25 W decreased emulsion stability (the Sauter diameter increased from 0.54 to 0.73 pm). At 32 W, the 10 and 90 percentiles of the droplet size distribution corresponded to 0.26 and 1.88 pm at 25 W, they corresponded to 0.30 and 3.69 pm. Further reducing the sonication power (to 17 W) provided a highly inhomogeneous... 

A study on the influence of the viscosity of the dispersed phase in the preparation of emulsions of vegetable oils (olive, soyabean and linseed) in water with US assistance revealed that replacing the oil with the highest viscosity and interfacial tension — olive oil — with soyabean oil, which has slightly lower viscosity and interfacial tension, caused virtually no reduction in droplet size. Linseed oil, with much lower viscosity and interfacial tension than olive oil, exhibited a much smaller Sauter diameter than the latter viz. 0.47 (xm versus 0.62 pm). Breaking low-viscosity droplets requires less vigorous cavitation shock waves than breaking more viscous ones [49]. 

The emulsification efficiency can be increased by increasing surfactant concentration in the medium in fact, emulsion droplets find it difficult to disperse and tend to grow large at low concentrations of surfactant. Figure 6.12C shows the variation of droplet size (expressed as the Sauter diameter, 0/3 2) in a w/o water-in-kerosene emulsion at variable... 

As an example, I would like to mention the effect of stirring speed on emulsion stability. In Figure 16, it can be seen that with increasing stirring speed in a homogenizer, the emulsion can be broken with less efficiency. This correlates with decreasing "Sauter diameter" Dp. The droplet diameter distribution of the emulsion becomes more and more uniform. The smaller the droplets, the smaller are the mutual attractive forces and the smaller is the probability of a collision of two particles. 

The HLD concept has been recently related to the so-called net-average curvature which indicates the size of the oil and water domains in the micro emulsion. For marginal microemulsions, i.e. of the WI or WII type at some distance from optimum, the inverse of the swollen micelle Sauter diameter is proportional to HLD. The zero net curvature at optimum does not result from infinite radius but rather from the coexistence of finite curvatures of opposite signs. For bicontinuous micro emulsions, it is the inverse of the characteristic length which is maximised at HLD = 0. As discussed elsewhere [38], its value at optimum formulation is the maximum distance that a molecule of oil or water can be separated from the surfactant layer and still interacts with it. In other words, it is the length at which the molecular interaction becomes equal to the molecular entropy. 

This corresponds to the ratio of arithmetic mean volume and arithmetic mean droplet surface and comprises the droplet size distribution of the investigated emulsions. For a theoretical monomodal size distribution [36] the Sauter diameter is approx, two times higher than the arithmetic diameter, because the influence of larger but less numerous droplets is more pronounced. 

Figure 13.9 gives an example of droplet volume density distributions of emulsions obtained by pressing an emulsion premix through a membrane at transmembrane pressure differences varying from 3 bar to 11 bar. These pressure differences are 7.5- to 27.5-fold the minimum pressure difference required (capillary pressure). A hydrophilic polyamide membrane with a mean pore size of 0.8 pm was used. The emulsion premix consisted of 20% dispersed phase (vegetable oil). As continuous phase water containing emulsifier Tween 80 at a concentration of 2% was used. The Sauter diameter of the emulsion premix was X3,2 = 25 pm. 

Figure 13.11 Sauter diameter of emulsions in dependence of the mean pore size of the membrane after the first, second and third passes. Disperse phase fraction (p = 5% emulsifier 2% Tween 80 transmembrane pressure difference 12 bar.

In the example given in Figure 13.11, polyamide membranes with different mean pore sizes were used (0.2 pm, 0.45 pm, 0.8 pm). A small disperse fraction of 5%, and a high emulsifier concentration (2% of emulsifier Tween 80) was chosen in order to avoid coalescence. Figure 13.11 gives Sauter diameters of the emulsions produced with membranes of different mean pore sizes after the first, second and third pass at 12 bar through the membrane. The Sauter diameter of the emulsion premix was 12 pm. 

After three passes through the membranes with pore sizes of 0.2 pm, 0.45 pm and 0.8 pm, Sauter diameters of, respectively, 0.9 pm, 1.0 pm and 1.2 pm could be obtained. The ratios between droplet size and membrane pore size, x/dp, were 4.5, 2.2 and 1.5, respectively. The smaller the pore size of the membrane, the bigger the capillary pressure (Equation 13.2) that has to be overcome to produce emulsions and consequently the bigger the ratio x/dp [32]. 

Influence of Disperse Phase Fraction With increasing dispersed phase fraction, droplet collisions and thus droplet coalescence frequencies increase. Therefore, usually, the lower the disperse phase concentrations, the smaller are the mean emulsion droplet sizes found. An example is given in Figure 13.13. In this example, an emulsion premix with 40% of dispersed phase and a Sauter diameter of... 

Figure 13.13 Sauter diameter of emulsions with different disperse phase concentrations as a function of the pressure difference. Membrane mean pore size 0.8 pm, one pass.

Figure 13.16 Voltage signal obtained from the pulse laser photometer by Inline monitoring of emulsion against Sauter diameter measured by the Coulter LS 230.

Figure 13.16 gives the voltage signal obtained from the pulse laser photometer against the Sauter diameter measured by the Coulter LS 230. The peaks between the different pressures are due to air bubbles and for this reason they are neglected. It depicts the good correlation between mean droplet size and optical density of an emulsion. 

The effect of repeating process can also be monitored by inline measurement, as shown in Figure 13.17. An o/w emulsion with 10% dispersed phase and 2% Tween 80 and Sauter diameter X32 = 13 pm was pressed three times by 12 bar through a membrane with a mean pore size of 0.45 pm. 

Fig. 21.36 Spray Sauter diameter of plant oil emulsions for six selected concentrations of Maltodextrin, atomizer geometry EAl was used, according to [9].

Fig. 21.38 Spray Sauter diameter of silicone oil emulsions for three different viscosity ratios and gas pressure of 4 bar, atomizer geometry EA2 was used...

Due to the adjusted viscosity of 37 mPa s for all emulsions, the Sauter diameters are equal at each ALR. For these measurements, the atomizer geometry EA2 made of PMMA was used to visualize the flow pattern inside the atomizer for emulsions... 

Correlations for the Sauter Mean Diameter of the Dispersed Phase Droplets/Globules in Oil/Water and Emulsion Systems... 

In this section, we discuss the effects of solids addition on the rheology of oil-in-water emulsions, in particular, the effects of solids size (size distribution) and shape (spherical versus irregular). Because the type of the oil used to form an emulsion is important in determining the viscosity of the oil-in-water emulsion, the rheology of the emulsion-solids mixtures is also influenced by the type of oil. Thus, two distinct emulsion systems with added solids will be discussed (1) synthetic (Bayol-35) oil-in-water emulsions 21, 57) and (2) bitumen-in-water emulsions (58). The synthetic oil has a viscosity of 2.4 mPa s, whereas the bitumen has a viscosity of 306,000 mPa s at 25 C. The Sauter mean diameter of the oil droplets is 10 xm for synthetic oil, and 6 xm for bitumen-in-water emulsions. The synthetic OAV emulsions are fairly shear-thinning, whereas the bitumen OAV emulsions are fairly Newtonian. 

Effect of Solids Addition. Figure 16 shows the variation of the viscosity with shear stress when solids are added to a synthetic OAV emulsion. The solids are sand particles with a Sauter mean diameter of 9 xm. The... 

Industrial liquid-liquid extraction most often involves processing two immiscible or partially miscible liquids in the form of a dispersion of droplets of one liquid (the dispersed phase) suspended in the other liquid (the continuous phase). The dispersion will exhibit a distribution of drop diameters d, often characterized by the volume to surface area average diameter or Sauter mean drop diameter. The term emulsion generally refers to a liquid-liquid dispersion with a dispersed-phase mean drop diameter on the order of 1 pm or less. 

The coupled equations had been solved by numerical computation using an implicit finite difference technique [34]. While solving the above equations, the emulsion globule size J32 (sauter mean diameter) was calculated by using the following correlation [35] ... 

Figure 4-4 Reaction front progress inside emulsion globules of various sizes with same sauter mean diameter of0.065 cm. From Ref. [33] with permission.

V, total volume of emulsion phase R, volume of external phase We, Weber number, pN Jj/a d22, sauter mean globule diameter p, density of the aqueous external phase N, stirring rate... 

McClements and Dungan reported, based on light scattering measurements, that the Sauter or surface-volume mean diameter of drops in a dilute emulsion of n-hexadecane in water remained constant while the number of drops decreased with time during solubilization of the hydrocarbon into a 2 wt% solution of Tween 20 (sorbitan monolaurate). Weiss et al. found similar results for the same surfactant with n-tetradecane and n-octadecane. This result, which seems surprising in... 

In the chemical industry (on the mega- as well as the micro-scale) fine emulsions have many useful applications in, e.g., extraction processes or phase transfer catalysis. Additionally, they are of interest for the pharmaceutical and cosmetic industry for the preparation of creams and ointments. Micromixers based on the principle of multilamination have been found to be particularly suitable for the generation of emulsions with narrow size distributions [33]. Haverkamp et al. showed the use of micromixers for the production of fine emulsions with well-defined droplet diameters for dermal applications [38]. Bayer et al. [39] reported on a study of silicon oil and water emulsion in micromixers and compared the results with those obtained in a stirred tank. They found similar droplet size distributions for both systems. However, the specific energy required to achieve a certain Sauter mean diameter was 3-1 Ox larger for the macrotool at diameters exceeding 100 pm. In addition, the micromixer was able to produce distributions with a mean as low as 3 pm, whereas the turbine stirrer ended up with around 30 pm. Based on energy considerations, the intensification factor for the microstirrer appears to be 3-10. 

One of the unique rheological features of emulsions is that the apparent viscosity of the emulsion can drop below the viscosity of the continuous phase when the concentration of the dispersed phase is low, normally below 0.1 in volume fraction (194). When solids are added to the emulsion, the apparent viscosity can decrease even further and the volume fraction of the dispersed phase at which minimum viscosity occurs increases with increasing solids content. Figure 30 shows the apparent viscosity of water-and-sand-in-bitumen, pwsh, variation with the solid-free water volume fraction, j8w, for two shear rate values. The experimental data were provided by Yan (private communication), where the system consists of 52 pm sand particles treated with hexadecyltri-methylammonium bromide (HAB) and water droplets of a Sauter mean diameter of 9 pm dispersed in bitumen at 60 °C. The sand particle volume fraction on water-free basis is j8s = 0.193. The range of the water droplet volume fraction, on a solid-free basis, jfrw is between 0 and 0.4. It can be observed that a minimum viscosity is present at a solid-free water droplet volume fraction of about 0.1. For a lower solid concentration, Ps = 0.113, the minimum apparent viscosity is found at /3W = 0.05... 

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