Surfactants stable emulsions

In the crude, water is found partly in solution and partly in the form of a more-or-less stable emulsion this stability is due to the presence of asphaltenes or certain surfactant agents such as mercaptans or naphthenic acids. 

If two pure, immiscible liquids, such as benzene and water, are vigorously shaken together, they will form a dispersion, but it is doubtful that one phase or the other will be uniquely continuous or dispersed. On stopping the agitation, phase separation occurs so quickly that it is questionable whether the term emulsion really should be applied to the system. A surfactant component is generally needed to obtain a stable or reasonably stable emulsion. Thus, if a little soap is added to the benzene-water system, the result on shaking is a true emulsion that separates out only very slowly. Theories of... 

The energetics and kinetics of film formation appear to be especially important when two or more solutes are present, since now the matter of monolayer penetration or complex formation enters the picture (see Section IV-7). Schul-man and co-workers [77, 78], in particular, noted that especially stable emulsions result when the adsorbed film of surfactant material forms strong penetration complexes with a species present in the oil phase. The stabilizing effect of such mixed films may lie in their slow desorption or elevated viscosity. The dynamic effects of surfactant transport have been investigated by Shah and coworkers [22] who show the correlation between micellar lifetime and droplet size. More stable micelles are unable to rapidly transport surfactant from the bulk to the surface, and hence they support emulsions containing larger droplets. 

At low temperature, nonionic surfactants are water-soluble but at high temperatures the surfactant s solubUity in water is extremely smaU. At some intermediate temperature, the hydrophile—Hpophile balance (HLB) temperature (24) or the phase inversion temperature (PIT) (22), a third isotropic Hquid phase (25), appears between the oil and the water (Fig. 11). The emulsification is done at this temperature and the emulsifier is selected in the foUowing manner. Equal amounts of the oil and the aqueous phases with aU the components of the formulation pre-added are mixed with 4% of the emulsifiers to be tested in a series of samples. For the case of an o/w emulsion, the samples are left thermostated at 55°C to separate. The emulsifiers giving separation into three layers are then used for emulsification in order to find which one gives the most stable emulsion. 

Oil-in-water emulsions provide a cost-effective alternative to the methods mentioned previously, namely, heating or diluting. A typical transport emulsion is composed of 70% crude oil, 30% aqueous phase, and 500 to 2000 ppm of a stabilizing surfactant formulation [1497]. Nonionic surfactants are relatively insensitive to the salt content of the aqueous phase ethoxylated alkylphenols have been used successfully for the formation of stable emulsions that resist inversion. 

A reduction in the electrical charge is known to increase the flocculation and coalescence rates. Sufficient high zeta potential (> — 30 mV) ensures a stable emulsion by causing repulsion of adjacent droplets. The selection of suitable surfactants can help to optimize droplet surface charges and thus enhance emulsion stability. Lipid particles with either positive or negative surface charges are more stable and are cleared from the bloodstream more rapidly than those with neutral charge [192, 193]. 

Emulsions. Emulsion fluids and foams came into routine use in competition with crosslinked fluids during 1970-80. Simple, barely stable emulsions had been used early in fracturing. These were mainly emulsified acids that "broke" when the acid spent on the formation surfaces. In the late 1960 s Kiel became a proponent of very high viscosity oil fluids as a method to place exceptional (at the time) amounts of proppant(337,338). To avoid the frictional resistance typical of gelled oils he advanced the concept of preparing a very viscous oil-external emulsion with one part fresh water, 0.1% sodium tallate surfactant, and two parts oil. The viscous emulsion had to be pumped simultaneously with a water stream to minimize frictional pressure. This process was clumsy and still... 

Since we still observed increased rates in the absence of inhibitor and in the presence of ultrasound (Fig. 5.35) we have explained the reduction or lack of an induction period in the presence of ultrasound in terms of two factors namely, a greater radical production both from enhanced initiator breakdown [74], and/or degradation of the polymer, and also from the creation of a far more stable emulsion. This latter point was confirmed visually. Depending upon the irradiation power and surfactant level employed, we were able to observe up to 40 % increase in initiator breakdown and a de-... 

Water-soluble l,3-bis(di(hydroxyalkyl)phosphino)propane derivatives were thoroughly studied as components of Pd-catalysts for CO/ethene (or other a-olefins) copolymerization and for the terpolymerization of CO and ethene with various a-olefins in aqueous solution (Scheme 7.17) [59], The ligands with long hydroxyalkyl chains consistently gave catalysts with higher activity than sulfonated DPPP and this was even more expressed in copolymerization of CO with a-olefins other than ethene (e.g. propene or 1-hexene). Addition of anionic surfactants, such as dodecyl sulfate (potassium salt) resulted in about doubling the productivity of the CO/ethene copolymerization in a water/methanol (30/2) solvent (1.7 kg vs. 0.9 kg copolymer (g Pd)" h" under conditions of [59]) probably due to the concentration of the cationic Pd-catalyst at the interphase region or around the micelles which solubilize the reactants and products. Unfortunately under such conditions stable emulsions are formed which prevent the re-use... 

When a surface-active substance is added to an oil-water system, the magnitude of IFT decreases from 50 mN/m to 30 (or lower [less than 1] mN/m. This leads to the observation that, on shaking, the decreased IFT of the oil-water system leads to smaller drops of the dispersed phase (oil or water). The smaller drops also lead to a more stable emulsion. Depending on the surfactant used, either an oil in water (O/W) or a water in oil (W/O) emulsion will be obtained. These experiments where oil and water, or oil and water + surfactant are shaken together, are shown in Figure 9.1. 

Nonionic surfactants such as sorbitan monooleate yield more stable emulsions than do ionic surfactants, However, the latices from inverse emulsion polymerizations are generally less stable than those from conventional emulsion polymerizations, and flocculation is a problem. 

In addition to environmental concerns, there are other driving forces for the development of cleavable surfactants. One such incentive is to avoid complications such as foaming or formation of unwanted, stable emulsions after the use of a surfactant formulation. Use of a cleavable surfactant instead of... 

Williams et al. have also investigated the effect of variation of the DVB content of the monomer phase on the cellular structure of the resulting foam [130]. The phase volume and surfactant and initiator concentrations were kept constant while the DVB content was increased from 0 to 100% this caused a drop in average cell size from 15 pm to 6 pm. The increased hydrophobicity of DVB compared to styrene probably results in a more stable emulsion, giving a slower rate of droplet coalescence and smaller average cell size. 

A stable emulsion requires balancing of hydrophobic and hydrophilic components into a uniform suspension. The suspension may be a multicomponent system of emulsifiers, surfactants, stabilizers, and thickeners that are included only to make an aesthetically pleasing product — not for their clinical significance. 

Emulsions made with a fine oil droplet particle size, usually less than one micron, are more stable with the oil droplets less likely to coalesce and separate. The encapsulation of a good quality emulsion is generally more efficient with less surface oil on the spray-dried powder. We wanted to build surfactant properties into the starch backbone to improve encapsulation efficiencies. Studies of the mechanism by which surfactants stabilize emulsions were made in order to accomplish this. 

Because of their large interfacial area, emulsions are basically unstable. In order to produce a stable emulsion, a surfactant is mostly needed. The surfactants are adsorbed at the oil-water interface, forming a link between the two phases of different polarity. For this purpose, a wide variety of emulsifying agents is currently available. Polysaccharides such as arabic gum, tragacanth, Karaya gum, and different seaweed carbohydrate polymers have been employed. They, however, show considerable batch-to-batch variations and might support microbial growth. 

EO)12-A as examples at the extremes of the HLB range available. In all cases both groups of surfactants emulsified the monomers styrene, MMA, and vinyl acetate (VAc). There was no difference between the conventional surfactants and their polymerization analogues with styrene. In the case of the MMA and VAc systems, the polymerizable surfactants yield much less stable emulsions than their non-polymerizable analogues. 

Molecules that self-assemble into reverse micelles with low surfactant properties are generally efficient extractants (such as HDEHP, TBP, malonamides, etc.). Their adsorptions at the interface permit the complexation of the aqueous solute and their low surfactant properties permits the avoidance of the formation of very stable emulsion. Hence, ions are extracted, but typically there is less than one water molecule per ion extracted. Exact determination of coextracted water is still important, however, for interpreting the conductivity values and for evaluating the polar core volumes. Typical values are found for the Hamaker constant, because polar cores are supersaturated salt solution. 

It is not possible to produce a dispersion of rubber particles in the thermoset precursors due to their agglomeration. It is possible, however, to synthesize a stable emulsion or suspension of rubber particles in one of the monomers. These particles, stabilized by copolymers and surfactants, may be considered as a limiting case of CSR particles when the shell thickness tends to zero. The use of dispersed acrylic rubbers (Sue et al., 1996a and Ashida et al., 1999) and poly(dimethyl-siloxane) (PDMS) emulsions (Rey et al., 1999), have been reported. 

Microemulsions are transparent or translucent, thermodynamically stable emulsion systems (Griffin 1949). Forming a middle phase microemulsion (MPM) requires matching the surfactant system s hydrophobicity with that of the oil. The HLB (hydrophilic-lipophilic balance) number reflects the surfactant s partitioning between water and oil phases higher HLB values indicate water soluble surfactants while lower values indicate oil soluble surfactants (Kunieda et. al. 1980, Abe et. al. 1986). While a balanced surfactant system produces middle phase microemulsions, an underoptimum surfactant system is too water soluble (high HLB) while an over-optimunTSystem is too oil soluble (low HLB). 

Most emulsions are not thermodynamically stable, but as a practical matter, quite stable emulsions can occur that resist demulsification treatments and may be stable for weeks/months/years. Most meta-stable emulsions that will be encountered in practice contain oil, water and an emulsifying agent (or stabilizer) which is usually a surfactant, a macromolecule, or finely divided solids. The emulsifier may be needed... 

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