Stability mixed emulsifier systems

The formation and stabilization of 0/W emulsions prepared with mixed emulsifier systems has been extensively investigated. However, the mechanisms proposed differ greatly. One of the primary hypotheses attributes the enhanced stability to the formation of a molecular "complex" or layer at the oil/water interface (8-11). The mixture of emulsifier types increases the packing density of the adsorbed interfacial film. Several investigators have shown that more closely packed complexes produce more stable emulsions (9,12-14). Friberg, et al. (15-17) have attributed the enhanced stability of mixed emulsifier emulsions to the formation of liquid crystals at the oil/water interface, which reduce the van der Waals attractive forces. 

Earlier conductivity measurements have indicated that the most stable miniemulsions are produced with mixed emulsifier molar ratios between 1 1 and 1 3 (22,23). This correlation agrees with a theoretical analysis of mixed emulsifier adsorption onto oil droplets by Lucassen-Reynders (35), who have determined the optimum stability to occur at molar ratios near 1 1. However, the maximum interfacial tensions at these molar ratios were unexpected because, minimum interfacial tensions are usually associated with maximum emulsion stability. In fact, minima values substantially less than 1 dyne/cm have been reported for several oil/mixed emulsifier systems (31,33, 36,37). 

The interfacial tension values increase from A.l dynes/cm for SLS/ decanol to 8.3 dynes/cm for SLS/octadecanol. Conductometric titration results have indicated that all of these mixed emulsifier systems, except the one with decanol, should give a relatively stable emulsion (22,23). Interestingly, the SLS/decanol mixed emulsifier solution was the only case in which the presence of the fatty alcohol reduced the interfacial tension with styrene to below the value measured for SLS alone. Studies are in progress to investigate this phenomenon and to determine the effect of alcohol chain length on miniemulsion stability. 

The presence of a thermodynamically incompatible polysaccharide in the aqueous phase can enhance the effective protein emulsifying capacity. The greater surface activity of the protein in the mixed biopolymer system facilitates the creation of smaller emulsion droplets, i.e., an increase in total surface area of the freshly prepared emulsion stabilized by the mixture of thermodynamically incompatible biopolymers (see Figure 3.4) (Dickinson and Semenova, 1992 Semenova el al., 1999a Tsapkina et al., 1992 Makri et al., 2005). It should be noted, however, that some hydrocolloids do cause a reduction in the protein emulsifying capacity by reducing the protein adsorption efficiency as a result of viscosity effects. 

These mixed-surfactant systems are used not only for their ability to form complex condensed films at the liquid-liquid interface, enhancing the stability of the emulsion, but also because of their ability to impart body to the product, resulting in a semisolid product rather than a liquid. Mixed emulsifiers control the consistency of a cream by forming a viscoelastic network throughout the continuous phase of the emulsion. The network results from the interaction of the mixed emulsifier with water, forming a liquid crystalline phase. 

Wherever this bridging is required, surfactants can be used. If pigment surfaces have poor attraction for binder molecules, surfactants can assist dispersion. When two liquids will not mix, surfactants will stabilize droplets of one liquid in the other, i.e. they will emulsify (Chapter 11). Different surfactants are required for different systems and different applications the nature and proportions of the two parts of the molecule will vary from use to use. 

Coimneicial production of emulsifiable concentrates often uses a matched pair emulsifier system. The matched pair uses two surfiu tant blends that are mixed at the iq>pnq>riate ratio to maximize the kinetic stability of die emulsion that is formed. One surfactant blend has a relatively low HLB, and the other surfactant blend has a relatively high HLB. These two blends ate mixed at various ratios until die optimal HLB for the desired s tem is found. 

Uses Food grade stabilizer cold mix emulsifier for cosmetics and pharmaceuticals cold hot emulsion system unique ambient temp, emulsifier which yields stable, aesthetic o/w emulsions Properties Powd. 100% cone. 

Emulsion Process. The emulsion polymerization process utilizes water as a continuous phase with the reactants suspended as microscopic particles. This low viscosity system allows facile mixing and heat transfer for control purposes. An emulsifier is generally employed to stabilize the water insoluble monomers and other reactants, and to prevent reactor fouling. With SAN the system is composed of water, monomers, chain-transfer agents for molecular weight control, emulsifiers, and initiators. Both batch and semibatch processes are employed. Copolymerization is normally carried out at 60 to 100°C to conversions of - 97%. Lower temperature polymerization can be achieved with redox-initiator systems (51). 

Water content and viscosity measurements in certain systems show a correlation to emulsion stability [597]. The viscosity provides a more reliable measure of emulsion stability, but measurements of the water content are more convenient. Mixing time, agent amount, settling time, and mixing energy impact the effectiveness of an emulsifier. 

Ice cream serves as a wonderful (and tasty) example of a complex, dynamically heterogeneous food system. A typical ice cream mix contains milk or cream (water, lactose, casein and whey proteins, lipids, vitamins, and minerals), sucrose, stabilizers and emulsifiers, and some type of flavor (e.g., vanilla). After the ingredients are combined, the mix is pasteurized and homogenized. Homogenization creates an oil-in-water emulsion, consisting of millions of tiny droplets of milk fat dispersed in the water phase, each surrounded by a layer of proteins and emulsifiers. The sucrose is dissolved in... 

Surfactants such as sulfated fatty alcohols may be hydrated to a higher extent than the fatty alcohols alone and thus stabilize o/w emulsions. The eombination of an anionic and a nonionic srrrfactant has proved to be partieularly effeetive, sinee the electrostatic repulsion forces between the ionie surfaetant moleeules at the interface are reduced by the incorporation of nonionic molecules, thus improving the emulsion stability. The combination of cetyl/stearyl sulfate (Lanette E) and eetyl/ stearyl alcohol (Lanette 0) to yield an emulsifying eetyl/stearyl aleohol (Lanette N) is an example of this approach. The polar properties of this srrrfactant mixtrrre are dominant, and o/w creams are formed. In contrast to w/o systems, the stabilizing effect of the surfactant mixtirre is not mainly due to adsorption at the interfaee. Instead, the mixed surfactants are highly hydrated and fonn a lamellar network, whieh is... 

In the early 1970s Li [13] proposed a method that is now called Emulsion (surfactant) Liquid Membrane (ELM) or Double Emulsion Membrane (DEM) (Fig. 3). The name reveals that the three liquid system is stabilized by an emulsifier, the amount of which reaches as much as 5 % or more with respect to the membrane liquid. The receiving phase R, which usually has a smaller volume than the donor solution, F of similar nature, is finally dispersed in the intermediate phase, M. In the next step the donor solution F is contacted with the emulsion. For this purpose, the emulsion is dispersed in the donor solution F by gentle mixing typically in a mixer-settler device. After this step, the emulsion is separated and broken. The enriched acceptor solution is further processed and the membrane liquid M is fed back for reuse. 

Another associated issue was the possibility of inactivating the LRES (lym-phoreticuloendothelial system). By analogy with other injectable systems, it could also be deduced that the injectable emulsion system needed to be sterile and apy-rogenic and free of acute or chronic toxicities from components or their associated degradation products. It also followed that the injectable system required to be stable, although how stability was to be determined and, more to the point, measured, has remained an issue to the present day. This is mainly because emulsions are thermodynamically unstable although their stability can be extended by formulation. As a result emulsion products are now available that are submicron in diameter, sterile, and stable for several years after preparation. In major part this has been due to the use of phospholipids as stabilizers and emulsifiers, in particular the mixed products identified as the lecithin of commerce. 

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