Emulsions droplet size range

The responses chosen all relate to important foam properties. We believed that yi, the emulsion droplet size, determines y2, the cell size in the resultant foam, and we wished to determine whether this is true over this range of formulations. The foam pore size ys should determine the wetting rate y7, so these responses could be correlated, and yg, the BET surface area, should be related to these as well. The density y and density uniformity ys are critical to target performance as described above, and ys, the compressive modulus, is an important measure of the mechanical properties of the foam. 

An emulsion is a dispersed system where one liquid phase is finely subdivided as globules or droplets and uniformly distributed in the other liquid phase. The practical application of emulsions and their technology applies to pharmaceutical and cosmetic formulations. The usual globular or droplet sizes range from 0.1 to 10 pm. 

Mouran et al. [105] polymerized miniemulsions of methyl methacrylate with sodium lauryl sulfate as the surfactant and dodecyl mercaptan (DDM) as the costabilizer. The emulsions were of a droplet size range common to miniemulsions and exhibited long-term stability (of greater than three months). Results indicate that DDM retards Ostwald ripening and allows the production of stable miniemulsions. When these emulsions were initiated, particle formation occurred predominantly via monomer droplet nucleation. The rate of polymerization, monomer droplet size, polymer particle size, molecular weight of the polymer, and the effect of initiator concentration on the number of particles all varied systematically in ways that indicated predominant droplet nucleation. 

The sizes of droplets can change depending on the physical-chemical properties of petroleum and water as well as the conditions of emulsion formation. Sizes range from 0.1 micron up to several tens of mm. Disperse systems which consist of droplets of the same size (single diameter) are referred to as mono-disperse. On the other hand, systems that consist of droplets of different sizes are called poly-disperse systems. Petroleum emulsions are poly-dispersed systems. 

Rather interesting demulsification methods were proposed recently [245] the use of membranes both of hydrophilic and hydrophobic nature to break down w/o emulsions and w/o/s mixtures. Hydrophobic membranes had pore sizes from 0.02 to 0.2 pm, and the dispersed aqueous phase droplet sizes ranged from 1 to 5 pm. The effect of water droplet retention is present even though the molecular weight of the water molecule (18) is much smaller than that of tetradecane (198) which was used as a model. 

Much of the work in this area has been done in emulsions having a droplet size of more than 1 pm, and the application of submicron (nano) emulsions in encapsulation of oils and flavors is relatively new in the literature. Some works have been carried out to determine the influence of submicron emulsions produced by different emulsification methods on encapsulation efficiency and to investigate the encapsulated powder properties after SD for different emulsion droplet sizes and surfactants. The process has been referred to as nanoparticle encapsulation since a core material in nanosize range is encapsulated into a matrix of micron-sized powder particles (Jafari et al., 2008). This area of research is developing. Some patents were filed in the past describing microemulsion formulations applied to flavor protection (Chung et al., 1994 Chmiel et al., 1997) and applications in flavored carbonated beverages (Wolf and Havekotte, 1989). However, there is no clear evidence on how submicron or nanoemulsions can improve the encapsulation efficiency and stability of food flavors and oils into spray-dried powders. 

The obvious application of the method is to determine emulsion droplet sizes. The NMR sizing method, which was apparently first suggested by Tanner in Ref. 24, has been applied to a number of different emulsions ranging from cheese to crude-oil emulsions (25-31). 

DT-100 from Dispersion Technology. All of them are claimed to be able to characterize emulsions in the wide droplet size range. There are some major differences between them. For instance, Opus was designed initially for large particles only because it employs the short wavelength requirement (21). 

Emulsion droplet sizes in the range from 1 to 50 jim can be measured with rather modest gradient strengths of about 1 T/m. Note that the size determination rests on measuring the molecular motion of the dispersed phase, so the method cannot be applied to dispersed phases with low molecular mobility. In practice, oils with self-diffusion coefficients above 10 m s is required for sizing of OAV emulsions. Of course, W/0 emulsions with most conceivable continuous media can be sized. 

Figure 8 Anal)4ically demanding emulsion droplets are largely coagulated into 3-D floes particles are present in the droplet size range. Such an image is extremely hard to analyze by automated software routines, and consequently demands strong participation by the operator. On the other hand, this procedure remains the only true alternative for handling such systems, as other techniques will not be able to resolve floes or even discriminate between particles and droplets.

O/W nano-emulsions with droplet radii in the range 26-66 nm could be obtained at surfactant concentrations between 4 and 8%. The nano-emulsion droplet size and polydispersity index decreases with increasing surfactant concentration. 

The main driving force for separation of suspensions or emulsions is gravity. Most suspensions or emulsions have particle or droplet size ranges whereby the Brownian diffusion kT (where k is the Boltzmann constant and T is the absolute temperature) of the particles or droplets is insufficient to overcome the gravity force (that is given by the mass of each particle x acceleration due to gravity g x height of the container I), i.e. 

Depending on the process conditions, the ratio of emulsion droplet size to membrane pore size is within a range of 2-10. Schroder for example reported a ratio between three and four [8]. 

Droplet Size Droplet size was determined on a Van tan Coulter counter (Model 4000, Zymo Instruments, India) after diluting the multiple emulsion 100 times with an external phase. The droplet size ranged from < 1.0 to 1.93 pm. Table 9.1 shows the droplet size and the polydispersity of the multiple emulsion formulations. The particle sizes of 6-MP loaded, coated, and uncoated multiple emulsions was nearly the same. The mean diameter of PEG-coated multiple emulsions was found to decrease with time, and it reached its minimum size after 6 to 8 hours. The size was reduced by nearly 15%, and the polydispersity was decreased from 0.18 to 0.09. Kim et al. (1995) found the separation of the aggregated multiple emulsion droplets to occur over several days of equilibration. In our case, it was few hours because of steric stabilization of individual particles surface coated (Vanderhoff and El Asser, 1988). 

The defined size ranges and limits are somewhat arbitrary since there are no specific boundaries between the categories. The transition of size ranges, either from molecular dispersions to colloids or from colloids to coarse dispersions, is very gradual. For example, an emulsion may exhibit colloidal properties, and yet the average droplet size may be larger than 1 pm. This is due to the fact that most disperse systems are heterogeneous with respect to their particle size [1-2]. 

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