Surfactants and Emulsification

The HLB is an indicator of the emulsifying characteristics of an emulsifier, but not its efficiency. Thus, while all emulsifiers having a high HLB will tend to promote 0/W emulsions, there will be a considerable variation in the efficiency with which those emulsifiers act for any given system. For example, usually mixtures of surfactants work better than pure compounds of the same HLB (see also Section 7.1.1). 

Very finely divided emulsions can be prepared by increasing the temperature of the system, forcing an O/W emulsion to invert to a fine W/O emulsion, then cooling the system, causing re-inversion with the formation of very small dispersed oil drops [119]. This method is termed the PIT method. 

In addition to influencing stability, the nature of the emulsifier can also have an influence on droplet size distribution, on the mean droplet size and also on emulsion viscosity [120] (see also Section 6.5.5). 

Foaming ability reaches its maximum at or above the cmc of the surfactant. 

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De-emulsification, ie, the breaking of foams or emulsions, is an important process, with the oU iadustry being a common one ia which the process is oftea critical. Chemical and particulate agents that displace the surfactant and permit an unstabilized iaterface to form are used for this purpose. 

The physico-chemical theory of surface activity is a vast field and no more than broad principles can be touched on here major reference sources exist for those who require more detail of the relationship between chemical structure and the various surfactant properties such as wetting, detergency and emulsification-solubilisation [32-36]. 

Control of the particle size while retaining precise control over the release rate is enabled by compartmentalization of the sol-gel solution into droplets of definite size. This can be achieved by emulsification of the sol-gel solution by mixing it with a solution composed of a surfactant and a non-polar solvent (Figure 2.13). When an active molecule is located in the aqueous droplet of a W/O emulsion, encapsulation occurs as the silicon precursors polymerize to build an oxide cage around the active species. By changing the solvent-surfactant combination, the particle size can be varied from 10 nm to 100 pm as the size of the particles is controlled by the size of the emulsion droplet, which acts as a nano-reactor for the sol-gel reaction (Figure 2.13). 

The contribution to t by emulsified oil in our experiments is considered negligible in the nonlonlc surfactant solutions due to the very low CMC values. In SDS solutions, the emulsification occurs at the very beginning when no NaCl is added to the solution and the turbidity Introduced by emulsification does not change with time. When NaCl is added to SDS solutions, the CMC becomes low and emulsification becomes unimportant as it will be shown in the following sections. 

M.J. Rang and C.A. Miller Emulsions and Microemulsions—Spontaneous Emulsification of Oil Drops Containing Surfactants and Medium-Chain Alcohols. Prog. Colloid Polym. Sci. 109, 101 (1998). 

M. J. Rang and C.A. Miller Spontaneous Emulsification of Oils Containing Hydrocarbon, Nonionic Surfactant, and Oleyl Alcohol. J. Colloid Interface Sci. 209, 179 (1999). 

Y. Sela, S. Magdassi, and N. Garti Newly Designed Polysiloxane-Graft-Poly (Oxyethylene) Copolymeric Surfactants Preparation, Surface Activity and Emulsification Properties. Colloid Polym. Sci. 272, 684 (1994). 

Recently, nonionic ortho ester surfactants have been used as emulsifiers for squalene, a polar oil [65]. In this case a polymer is used together with the surfactant. The emulsification is made under acidic conditions, and the surfactant breaks down rapidly after the emulsion is formed, leaving a surfactant-free, polymer stabilized emulsion with reasonable stability. 

The point at which, supposedly, 50% of the acid species is transformed in salt corresponds to the half-neutrahzation, i.e., when half the alkahne required to reach the equivalence point has been added. This position corresponds to a buffer zone in which the variation of pH is small with respect to the amoimt of added neutralization solution (Fig. 14 left plot). Hence, in this region a very slight variation of pH can produce a very large variation of neutralization (Fig. 14 right plot), i.e., a considerable alteration of the relative proportion of AH and A . Far away from this pH, the opposite occurs. Consequently, the pH could be used to carry out a formulation scan, but the scale is far from hnear and the variation of pH does not render the variation of the characteristic parameter of the actual surfactant mixture that is at interface [77,78]. The appropriate understanding of the behavior of this kind of acid-salt mixture is particularly important in enhanced oil recovery by alkaline flooding [79,80] and emulsification processes that make use of the acids contained in the crude oils [81-83]. 

The removal of liquid oily soils from surfaces is generally understood in terms of three basic mechanisms the roll - back of droplets of oily soil, the surfaces of which are modified by the presence of an adsorbed layer of surfactant direct emulsification of macroscopic droplets of soil and the direct solubilization of the oily soil into surfactant micelles or other interfacial phases formed (1-3). 

Acid-in-oil emulsion can extend the propagation of acid considerable distances into a reservoir because the continuous (oil) phase prevents or minimizes contact between the acid and the rock [4,678,689]. Emulsification also increases viscosity and will improve the distribution of the acid in layered and heterogeneous reservoirs. Acidizing foams are aqueous, in which the continuous phase is usually hydrochloric acid (carbonate reservoirs) or hydrofluoric acid (sandstone reservoirs), or a blend, together with suitable surfactants and other stabilizers [345,659]. Foaming an acidizing fluid increases its effective viscosity, providing mobility control when it is injected [678]. 

In addition to the surfactant and epoxy resin, the parameters of the emulsification process will significantly influence the properties of the final emulsion. To obtain the smallest achievable droplet size with a narrow droplet size distribution, it is essential to optimize process parameters such as temperature of emulsification and mix ratio of surfactants when more than one surfactant is used. 

Uniqema Synperonic Surfactants, Resin Emulsification for Waterborne Coating and Adhesives, Uniqema, Wilmington, DE, 1999. 

Surfactants based on aliphatic alcohols are used as cleaners in both domestic and industrial applications. They provide excellent properties such as wetting, dispersion, and emulsification. The ethoxylates derived from alkylphenols are chemically stable and highly versatile, finding more use in industrial practice than in domestic applications. They are used both as processing aids and as components in various products. Their applications include metal cleaning, hospital cleaners and disinfectants, agricultural chemical formulation surfactants, insecticides and herbicides, oil-well drilling fluids, and many others. 

Rang, M.J., and Miller, C.A. (1999). Spontaneous emulsification of oils containing hydrocarbon, nonionic surfactant, and oleyl alcohol. J. Colloid Interface Sci., 209, 179-192. 

With cetyl alcohol, there is the complication that the polarity of the molecule may cause it to reside at the surface of the droplet, imparting additional colloidal stability. Here, the surfactant and costabilizer form an ordered structure at the monomer-water interface, which acts as a barrier to coalescence and mass transfer. Support for this theory lies in the method of preparation of the emulsion as well as experimental interfacial tension measurements [79]. It is well known that preparation of a stable emulsion with fatty alcohol costabilizers requires pre-emulsification of the surfactants within the aqueous phase prior to monomer addition. By mixing the fatty alcohol costabilizer in the water prior to monomer addition, it is believed that an ordered structure forms from the two surfactants. Upon addition of the monomer (oil) phase, the monomer diffuses through the aqueous phase to swell these ordered structures. For long chain alkanes that are strictly oil-soluble, homogenization of the oil phase is required to produce a stable emulsion. Although both costabilizers produce re-... 

Emulsification and Emulsion Polymerization of Styrene Using Mixtures of Cationic Surfactant and Long Chain Fatty Alcohols or Alkanes as Emulsifiers... 

TABLE IV. Static Emulsification Tes ts Performed with Surfactants and Oelaware-Childers Oil... 

EMSORB Sorbitan Fatty Acid Esters are lipophilic emulsifiers and coupling agents serving as integral components of emulsif-iable Industrial mold release agents, textile fiber and yarn lubricants, and textile finishing softeners. They are widely used as surfactants and functional components in many kinds of Industrial and household products. 

Is a water-soluble surfactant widely used for general purpose detergency, wetting, and emulsification. 

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