Surfactants emulsification methods

Different methods are used in microemulsion formation a low-energy emulsification method by dilution of an oil surfactant mixture with water and dilution of a water-surfactant mixture with oil and mixing all the components together in the final composition. These methods involve the spontaneous formation of microemulsions and the order of ingredient addition may determine the formation of the microemulsion. Such applications have been performed with lutein and lutein esters. ... 

N. Uson, MJ. Garcia, and C. Solans Formation of Water-in-Oil (W/O) Nano-Emulsions in a Water/Mixed Non-Ionic Surfactant/Oil Systems Prepared by a Low-Energy Emulsification Method. Colloid and Surfaces A Physicochem. Eng. Aspects 250, 415 (2004). 

The emulsification method is primarily used for waterborne epoxy adhesive systems and is the focus of this section. The epoxy resin is made water-dispersible by partitioning the epoxy resin within a micelle, effectively separating the resin from the water. This emulsification can be achieved by a suitable surfactant. 

Figure 14.1 Schematic representation of the experimental path in two emulsification methods. Method A. addition of decane to water/surfactant mixture Method B. addition of water to decane/Brij 30 solutions.

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. 

There are many industrial processes in which the formation of low internal phase or concentrated emulsions needs to be controlled in terms of formation, stability, destruction or prevention. Examples range from asphalt emulsions to personal care products, and to food products. Success in emulsion control requires achieving the right physical chemistry and also the right fluid mechanics. In addition to HLB (see Section 7.2.1), both the nature of the emulsification method and the oil-water ratio are critical in determining the produced emulsion type. It appears that the emulsification technique (applied shear and oil-water ratio) used can be of greater importance in determining the final emulsion type than the HLB values of the surfactants themselves. 

Nature of nanoparticle Emulsification method Nature of nanoemulsion Monomers Surfactants Polymerization and emulsification parameters Particle size (nm) References... 

A study of the phase behavior of water/oil/surfactant systems demonstrated that emulsification can be achieved by three different low energy emulsification methods (A and B as schematically shown in Fig. 2.8). Method A stepwise addition of oil to a water surfactant mixture. Method B stepwise addition of water to a solution of the surfactant in oil. Method C mixing all the components in the final composition, pre-equilibrating the samples prior to emulsification. In these studies, the system water/Brij 30 (polyoxyethlene lauryl ether with an average of 4 moles of ethylene oxide)/decane Wcis chosen as a model to obtain 0/W emulsions. The results showed that nanoemulsions with droplet sizes of the order of 50 nm were formed only when water was added to mixtures of surfactant and oil (method B) whereby inversion from W/0 emulsion to 0/W nanoemulsion occurred. 

Figure 11.13a shows a microemulsion of the 0.1 M NaCI aqueous solution/Ci2E4/ decane system with 90% aqueous solution and an oil/surfactant ratio of 2.33, at 7°C. The HLB temperature of this system is approximately 18 C. When the sample is rapidly brought to a higher temperature, 40 C in the experiment shown in Figure 11.13b, the sample becomes milky in less than 40 s. If the test tube is inverted, no flow is observed, an indication that complete emulsification has been achieved. The emulsions produced by this emulsification method have finer and narrower droplet size distributions (Figure 11.14) than those obtained by the usual methods. 

In this chapter, nano-emulsion formation by low-energy emulsification methods, with special emphasis on phase inversion methods and their relation to surfactant phase behavior will be discussed first. This will be followed by an analysis of nano-emulsion functional characteristics. The relation with their structure is discussed regarding the applications in which they are relevant. Prior to discussing nano-emulsion functional characteristics, the main nano-emulsion destabilization mechanism, Ostwald ripening, is described. 

In self-emulsification or direct emulsification methods, a solution of the oil and surfactant in an appropriate solvent (that is also soluble in the continuous aqueous phase) is simply added to water to form oil-in-water (0/W) emulsions in one step, under agitation. Similarly, a solution of water and surfactant in an appropriate solvent (also soluble in the oil phase) is added to the oil to form water-in-oil (W/0) emulsions [19]. It is called direct or self-emulsification because the emulsion is just obtained by a dilution process without any phase inversion. This method uses the chemical energy of dissolution in the continuous phase of the solvent present in the initial system (which is going to constitute the dispersed phase). When the intended continuous phase and dispersed phase are mixed. 

Microcapsules of PCL and its copolymers may be prepared by aircoating (fluidized bed), mechanical, and, most commonly, solution methods. Typically, the solution method has involved emulsification of the polymer and drug in a two-phase solvent-nonsolvent mixture (e.g., CH2Cl2/water) in the presence of a surfactant such as polyvinyl alcohol. Residual solvent is removed from the tnicrocapsules by evaporation or by extraction (70). Alternatively, the solvent combination can be miscible provided one of the solvents is high-boiling (e.g., mineral spirits) phase separation is then achieved by evaporation of the volatile solvent (71). The products of solution methods should more accurately be called microspheres, for they... 

Studies of flow-induced coalescence are possible with the methods described here. Effects of flow conditions and emulsion properties, such as shear rate, initial droplet size, viscosity and type of surfactant can be investigated in detail. Recently developed, fast (3-10 s) [82, 83] PFG NMR methods of measuring droplet size distributions have provided nearly real-time droplet distribution curves during evolving flows such as emulsification [83], Studies of other destabilization mechanisms in emulsions such as creaming and flocculation can also be performed. 

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