The Continuous Phase in an Emulsion

Emulsion

An emulsion can be defined as a mixture of two or more immiscible phases with a third component (an emulsifier) to stabilize the dispersed droplets.

From: Nanoscience in Dermatology , 2016

Explosives and Detonators

Zong-Xian Zhang , in Rock Fracture and Blasting, 2016

8.13.3 Emulsion Explosives

Emulsion explosives can well hold their packing and pumping properties stable over a wide range of temperatures. This stability is excellent, and the detonation properties can be kept constant even after longtime storage. Therefore, emulsions can be safely used in precharge in underground mining. The detonation velocity of emulsion explosives is much higher than that of ANFO, so emulsion explosives are suitable for hard rocks whose sonic velocity is usually equal to or smaller than the VOD of the explosives. Emulsion explosives are excellently water-resistant, so they can work very well in wet holes. Another advantage of emulsions is they are suitable for highly controlled mechanical charging.

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Persistent Fat Malabsorption in Cystic Fibrosis

Frank A.J.A. Bodewes , ... Henkjan J. Verkade , in Diet and Exercise in Cystic Fibrosis, 2015

41.2.1 Emulsification

Emulsification of triglycerides is a process in which (water-insoluble) fat droplets are suspended in an aqueous environment. Emulsification can be achieved by mechanical as well as biochemical means. Mechanical emulsification is attained by chewing and forcing dietary fat through a small opening (e.g., the pylorus) with high pressure, thus dispersing large fat droplets into smaller droplets. Biochemical emulsification is attained by the action of bile and gastric lipases and prevents the emulsion from recoalescing. Emulsification results in a fine, relatively stable oil-in-water emulsion with an increased surface area. Emulsification aids in the efficiency of fat absorption because the water soluble digestive/lipolytic enzymes are active at the site of the water–oil interface. Increasing the surface area will thus increase the rate of lipolysis.

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Membrane Contactors and Integrated Membrane Operations

E. Piacentini , ... E. Drioli , in Comprehensive Membrane Science and Engineering, 2010

4.03.10 Conclusions and Perspectives

The ME introduced in 1990 has received in the initial years a strong impulse shown by an increasing number of patent published in that period. It is, however, more recently that the potentialities of such technology have led to a higher number of applications in various fields. Productive plant for niche applications shows the advantages of the technology. The benefits of ME process for the emulsion field include low shear properties, especially for the preparation of double emulsions or emulsions containing shear-sensitive ingredients, and to control microstructured fabrication of fine particles. The limitations of ME process include low dispersed phase flux and fouling phenomena. However, its full exploitation at the industrial level is still not achieved. In particular, membranes specifically designed for emulsification process are required in order to intensify emulsification process and to meet the demanding requirements for size-controlled emulsions for specific applications.

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Multifunctional nanosized emulsions for theragnosis of life threatening diseases

Tamilvanan Shunmugaperumal , ... Ruchi Sharma , in Nanostructures for Drug Delivery, 2017

1.3 Concept of Multifunctional Nanosized Emulsions

Emulsions are biphasic and liquid-retentive formulation, which consists of two immiscible liquids: oil and water. If the amount of oil phase is significantly low when compared to the amount of water phase, then the final emulsion is termed as o/w emulsion. Conversely, when the amount of water phase is significantly lower than the oil phase, the resulting emulsion system appears to be somewhat more viscous and is called as water-in-oil (w/o) emulsion. Both o/w- and w/o-type of emulsion systems are stabilized against the aggregation, coalescence, and separation of dispersed oil or water phase by the addition of a third component called as emulsifying agent or emulgent or emulgator. In fact, therapeutic emulsions are being stabilized by the addition of more than one emulgent molecule in order to prevent random collision of—and then the coalescence of—dispersed oil or water phase of the o/w or w/o emulsion. Mixing of appropriate amounts of oil, water, and emulgent leads to the formation of an emulsion and this whole process is called emulsification. Apart from the amount of dispersed oil or water phase, which determines the type of final emulsion formed (whether o/w or w/o), the amount of single or multiple emulgent molecule added during the emulsification process will obviously control the type of emulsion produced. In addition, the size-reduction equipments such as high-energy or low-energy homogenizer used to mix the oil and water phases along with single or multiple emulgent molecules will also direct the final emulsion produced in terms of mean size of the dispersed phase in the final emulsion. Interestingly, both high- and low-energy homogenizers will generate emulsions with nanorange droplet particle sizes of the dispersed phase. However, an emulsion generated by the low-energy or spontaneous emulsification process is called microemulsion. On the other hand, an emulsion produced by means of the high-energy homogenizers is called nanoemulsions or nanosized emulsions (NE). Again, there are three basic differences between microemulsion and NE. First, the microemulsion possesses the dispersed phase droplet diameter value well below the range of 100 nm, typically even below 10 nm, as well. But the dispersed phase droplet diameter of the NE lies above 100 nm that, too, in the 300–500 nm level. Second, the notable difference between these two emulsions is their physical appearance. While the microemulsion creates a solution-like transparent appearance, the NE looks like a slightly bluish-colored white milk. Third, a moderately higher amount of single or multiple emulgent molecules is used for producing the microemulsion when compared to the emulsifier molecules' amount, which is being utilized to prepare the NE. In spite of these three basic differences between microemulsion and NE, these two terms (micro- and nanoemulsions) are, however, used interchangeably in many medical and pharmaceutical literatures. This chapter deals only with the o/w emulsion consisted of relatively low amounts of single or multiple emulgent molecules (in comparison to the high emulgent amount used to produce the microemulsion), and produced by the high-energy homogenizer equipments.

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EMULSIFIERS | Organic Emulsifiers

T. Kinyanjui , ... S. Mahungu , in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003

Stabilization by Macromolecules and Finely Divided Solids

Emulsion stability can be increased by the addition of macromolecules like gums and protein. Colloids like xanthan gum, carboxy methyl cellulose and guar gum significantly increase emulsion stability. With both a constant emulsifier and colloid concentration, emulsion stability is enhanced by increased emulsification temperature, increasing the degree of shear, and increase pH, in the range of 3–6. Colloids act by either increasing the viscosity or partitioning into the o/w interface and providing a physical barrier to coalescence.

To evaluate emulsion stability and thereby characterize the potential of an emulsifier, the rate at which the combined destabilization phenomena occur must be determined. These rates can be determined from the changes in the size and distribution of the oil droplets with time. There are several methods available for this determination. Nuclear magnetic resonance is often preferred as a better indication of stability to HLB values. Other methods, used to evaluate the effects of processing on emulsion stability, include centrifugation, turbidity light micoscopy scanning electron microscopy, etc.

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Membrane Contactors and Integrated Membrane Operations

M.E. Vilt , ... N.N. Li , in Comprehensive Membrane Science and Engineering, 2010

4.04.2.1.1 Emulsion liquid membrane system

An ELM is a three-phase system and can consist of water/oil/water (W/O/W) or oil/water/oil (O/W/O) phases. In either system, the liquid membrane is the phase separating the like phases. For a W/O/W system, the oil phase separating the two aqueous phases is the liquid membrane phase [11]. The ELM process can be described in four steps, which are shown in Figure 1 [12].

Figure 1. Emulsion Liquid Membrane Process. From Correia, P. F. M. M., de Carvalho, J. M. R. J. Membr. Sci. 2000, 179, 175–183.

The first step in forming an ELM is the formation of an emulsion between two immiscible phases. This is typically done with the use of surfactants and high-speed agitation. Emulsion droplets range from 1–3  μm in diameter, thus providing good stability [11]. Second, the emulsion is dispersed in a third continuous phase with constant agitation. Once dispersed in the continuous phase, globules of the emulsion of a diameter of 100–2000   μm form [11]. The mixing rate in the dispersion step is an important operating parameter. If dispersing speed is too fast, emulsion breakage can occur, and if too slow, large globules can form, reducing the mass transfer area. During this second step of the ELM process, mass transfer from the external phase to the internal phase occurs by one of the two facilitated transport mechanisms. After the desired separation, the emulsion and the continuous phase are separated in a settling step. The final step in the ELM process involves breaking the emulsion, whereby the internal phase is then recovered and the membrane phase can be reused. The emulsion is usually broken by the use of an electric field [13].

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Emulsions and Microemulsions for Topical and Transdermal Drug Delivery

Guang Wei Lu , Ping Gao , in Handbook of Non-Invasive Drug Delivery Systems, 2010

3.1.1.1 Emulsions

Emulsions are heterogeneous systems composed of at least two immiscible liquids, water and oil, one of which is usually uniformly dispersed as fine droplets throughout the other liquid phase by a mechanical agitation process. Emulsions are considered as a type of liquid–liquid colloid. The phase existing as small droplets is called the dispersed phase and the surrounding liquid is known as the continuous phase. Emulsions are commonly classified as oil-in-water (O/W) or water-in-oil (W/O) depending on whether the continuous phase is water or oil.

Emulsions are thermodynamically unstable as the dispersed and continuous phases can revert back as separate phases, oil and water, by fusion or coalescence of droplets. However, emulsions are commonly stabilized by an emulsifying agent, often referred to as a surfactant. In general, after vigorous agitation of the two immiscible phases, the more rapidly coalescing droplets form the continuous phase. This is usually the liquid that is present in the larger amount – the greater the number of droplets, the higher the probability of collision and coalescence. Therefore, emulsification can be considered as the result of two competing processes that occur simultaneously, namely the disruption of bulk liquids to produce fine droplets and the recombination of the dispersed droplets back to the bulk liquids. Theoretically, the dispersed phase of an emulsion can occupy up to 74% of the phase volume, and such high internal phase O/W emulsions have been produced with suitable surfactants (Eccleston, 2007). It is more difficult to formulate a W/O emulsion with greater than 50% dispersed phase because of the steric mechanisms involved in the physical stability. Although the droplet diameters of emulsions may vary enormously depending on their composition and manufacturing process, pharmaceutical and cosmetic emulsions are typically polydispersed with droplet sizes ranging from 0.1 to 100 μm.

With the application of surfactants and/or cosurfactants, the resulting emulsion is dictated by the relative solubility of these surfactants in oil and water. Usually, the phase in which the surfactant is most soluble becomes the continuous phase. Thus, hydrophilic surfactants promote O/W emulsions whereas lipophilic surfactants promote W/O emulsions. A range of different types of emulsifying agents are used in emulsion formulations, the individual emulsifying agents functioning on different principles to achieve a stable product. As a result, it is not easy to develop a universal theory that would account for emulsification and emulsion stability.

Emulsions are commonly used for topical pharmaceutical and cosmetic products, such as lotions and creams. The largest group of emulsions commercially available as medicines are dermatological products for topical application. Emulsions can be designed to facilitate drug penetration into and/or through the skin. Both O/W and W/O emulsions have been extensively used to deliver drugs and cosmetic agents to the skin, depending on the property of active agents and the indications of the medicines. Although the microstructure of many of these complex emulsions is now better characterized and understood, the underlying mechanisms by which the structure of an emulsion and the function of individual excipient (e.g. penetration enhancing agent) can influence drug bioavailability are far from clear. Droplet size of the emulsion may influence the drug penetration through the skin, but the effect often is not clinically significant. The evaporation of volatile excipients can occur and so affect the drug permeation across the skin. Judicious selection of an appropriate emulsifying agent and additional stabilizer is a critical factor in the design and development of emulsions. These factors will be discussed in more detail later.

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Microscopy

Arun Kumar Sharma DSc, FNA, FASc , Archana Sharma DPhil, DSc, FNA, FASc , in Chromosome Techniques (Third Edition), 1980

Coating with liquid emulsion

For emulsion film on glass plate, cut the film with a blade parallel to the four edges at 1.27 cm from the edge. Slowly peel away the emulsion from the glass plate, blowing moist air at the point of bonding; films on 35 mm film-base can also be similarly peeled off. Place the free emulsion strip in distilled water at 18–20 °C, for 10 min, transfer it to a 50 ml beaker on a water bath at 37 °C, cover, and allow the emulsion to melt completely without stirring (15 min).

For the bulk emulsions (gels), transfer about 2 ml of the emulsion to a 50 ml beaker with a clean glass spatula.

In both cases, warm the slides and with the warm slide held horizontally between the thumb and the forefinger of one hand, apply two drops of emulsion per square inch of slide from a medicine dropper. Spread the drops quickly with a brush (previously warmed) over an area already outlined by a diamond pencil scratch, rotate the slide from side to side so that the emulsion flows evenly over the area, and keep the slide in the warm condition for 30–60 s for uniform spreading of the emulsion, then transfer to cold temperature for 30 min to harden the emulsion.

The other method, which is more convenient, though requiring more emulsion, is to keep the melted emulsion (melted at 42–45 °C) in a long trough, and dip the subbed slide in it for 4–5 s followed by draining off the emulsion.

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Encapsulation of Phase Change Materials

Halime Paksoy , ... Yeliz Konuklu , in Encyclopedia of Energy Storage, 2022

Emulsion polymerization

Emulsion polymerization provides an economical and simple method for radical chain polymerization. For this reaction, firstly, a water-insoluble monomer must be dispersed in emulsion and polymerization must be continued here.

Tetradecane, pentadecane, hexadecane, and heptadecane, was microencapsulated in poly(styrene-co-ethylacrylate) using an emulsion copolymerization method. The best core/shell mass ratio was determined as 3:1 by Konuklu et al. (2015). In another study, Konuklu and Paksoy (2017) and Konuklu (2014) synthesized caprylic acid microcapsules with polystyrene and polyethylacrylate shell material using the emulsion polymerization method. In a study in the literature, emulsion method was used to synthesize n-Docosane/poly methyl methacrylate (PMMA) and n-Docosane/PMMA-1-dodecanethiol (DDT) microcapsules using 1-dodecanethiol as the chain transfer agent as presented in Fig. 27 (Jang et al., 2019). On the other hand, sodium sulfate decahydrate has been microencapsulated within a silica shell using emulsion polymerization (Zhang et al., 2019a,b).

Fig. 27. Emulsion polymerization method (Jang et al., 2019).

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Monitoring Crystallization in Simple and Mixed Oil-in-Water Emulsions using Ultrasonic Velocity Measurement

Eric Dickinson , ... Malcolm J.W. Povey , in Food Polymers, Gels and Colloids, 1991

Publisher Summary

Emulsion stability is an important consideration in the food industry, having a bearing on the shelf life and the microbiological quality of many food products. The degree of crystalline of fat droplets in food oil-in-water emulsions is an important factor affecting the stability of the colloidal system and the distribution of solute molecules between dispersed and continuous phases. This chapter discusses monitoring crystallization in simple and mixed oil-in-water emulsions using ultrasonic velocity measurement. It concludes that ultrasonic velocity measurement is a rapid, simple, and reliable way of following crystallization and melting in emulsion droplets. In mixed oil systems, the sensitivity of the technique allows the identification of crystallization in different kinds of oil droplets, of which composition may be changing with time due to rapid mass transport between droplets, notably when the emulsion is stabilized by water-soluble low molecular weight surfactant. The techniques described in the chapter are, in principle, applicable to the study of crystallization in triglyceride emulsions, although the situation is complicated in such systems due to the effects of polymorphism, impurities, and the wide range of lipid components present in even the purest of food oils.

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