Large concentrations of surfactants

Since there are various types of fluids, there are different kinds of dispersions that might be encountered in EOR. Fluids may be liquid, gaseous, or in the supercritical state. In EOR, gases are sometimes further classified as condensible (i.e., steam) or as not condensible into a liquid state of essentially the same composition. Certain fluids that contain sufficiently large concentrations of surfactant are termed microemulsions. Hence, depending on the type of oil recovery process and the conditions employed, a dispersion might be a so-called "oil-in-water" emulsion, an emulsion in which one of the fluids is a microemulsion, a foam (i.e., a dispersion of gas in a liquid), or a dispersion in which one of the phases is a supercritical fluid. 

The formation of bicontinuous microemulsions is conditioned by the nature of the monomer which is present in large amounts (up to by weight and which e.terts a great effect on the HLB and interfacial properties of the systems. Furthermore as the polynerirable microemulsicns contain a fairly large concentration of surfactant(s), interactions between surfactants and monomers cannot be neglected, especially when the latter are electrolytes. 

Also other species may cause depletion interaction. A case in point is surfactant micelles, for example, if an emulsion has been made with an unnecessary large concentration of surfactant, so that micelles remain after emulsification, this may cause aggregation of the droplets. In foods, however, the surfactant concentrations needed for depletion flocculation to occur are generally unacceptable. 

Use of a large concentration of surfactant and co-surfactant necessary for stabilizing the nanodroplets. 

Micro-emulsion Swollen monomer micelles dispersed in a continuous phase fairly large concentrations of surfactants required initiator dissolved in continuous phase Polymerisation initiated in the course of nucbation of monomer micelbs process characterised by continuous nucleation during entire reactbn fast rate of polymerisation (< 30 min) Particbs of very small si (diameter <100 nm) and narrow distribution polymer with ultra-high molecular weight (> 10 g/mol) copolymers with well-defined, homogenous composition... 

Micro-emulsion is another variant of emulsion polymerisation. Such emulsions are thermodynamically stable systems including swollen monomer micelles dispersed in a continuous phase. In general, they require fairly large concentrations of surfactants to be produced compared with the other dispersed polymerisation systems. Hence, the interfacial tension of the oil/water is generally close to zero. Polymers with ultra-high molecular weight, i.e. above 10 g/mol, can be obtained, as can copolymers with a very well-defined, homogenous composition. Whereas polymerisation can take 24-48 h in the normal emulsion process, it proceeds at a fast rate in micro-emulsion, as total conversion can be obtained in less than 30 min. Polymer particles of very small size (diameter < 100 nm) and narrow distribution can be obtained by this process. 

Alcohol sulfates are excellent foaming surfactants. According to the Kitchener and Cooper classification [148], alcohol sulfates form metastable foams. However, quantitative values cannot easily be compared because foam largely depends not only on the instrument used to produce and evaluate foam but also on the concentration of surfactant, impurities, temperature, and many other factors. In addition, a complete characterization of the foam capacity should take into account the initial amount of foam, its stability, and its texture. 

In binary mixtures of water, surfactants, or lipids the most common structure is the gyroid one, G, existing usually on the phase diagram between the hexagonal and lamellar mesophases. This structure has been observed in a very large number of surfactant systems [13-16,24—27] and in the computer simulations of surfactant systems [28], The G phase is found at rather high surfactant concentrations, usually much above 50% by weight. 

An additional point is that relatively high concentrations of surfactant, oil and cosurfactant are often used in microemulsions. Thus the volume of the microemulsion pseudophase is large and droplet-bound reactants are therefore diluted. Generally speaking, rate enhancements increase in the sequence microemulsions < micelles < vesicles simply because of a decrease in the volume of the micellar or droplet pseudophase. 

In the Will case, provided that there is enough surfactant but not too much, e.g., 1 wt. %, the system splits into three phases, i.e., a microemulsion in equilibrium with excess water and excess oil. At a higher surfactant concentration than the top vertex of the 3

single phase microemulsion often called WW behavior is attained. However, this occurrence generally requires a large amount of surfactant, e.g., 20 wt. %, which is in most practical cases too much for cost reasons. At a very low surfactant concentration, around the CMC, only two phases are in equilibrium, and the tension is not necessarily very low. Hence, the convenient surfactant concentration to carry out a phase behavior study is in the range 0.5-3 wt. % for which three-phase behavior and a very low inter facial tension is exhibited in most Will cases. 

Typical emulsion polymerization recipes involve a large variety of ingredients. Therefore, the possibilities of variations are many. Among the variables to be considered are the nature of the monomer or monomers, the nature and concentration of surfactants, the nature of the initiating system, protective colloids and other stabilizing systems, cosolvents, chain-tranfer agents, buffer systems, short stops, and other additives for the modification of latex properties to achieve the desired end properties of the product. 

When Co grows, the network volume slightly decreases and the concentration of surfactant q within the network increases. When cjj, exceeds a critical concentration of micelle formation (at this point cq = c, see Figs.14,15), the network collapses because the surfactant molecules aggregated in micelles cease to impose osmotic pressure which causes additional expansion of the network. At relatively small values of the ratio Vf/V, the collapse is continuous (Figs. 14, 15), so that the number of surfactant molecules in micelles increases from zero starting at the concentration c. However, when the ratio Vf/V is sufficiently large, a discrete first-order phase transition takes place. 

Most of the experimental and theoretical work on the aggregation of ionic surfactants in water has been devoted to understanding how this phenomenon is affected by such factors as concentration, temperature or chemical nature of the surfactants. Much less is known as to how surfactant aggregation is affected by an increase in hydrostatic pressure. Advances in the technique of high pressure vibrational spectroscopy (FT-IR and Raman) of aqueous systems have allowed us now to examine the effect of hydrostatic pressure on the structural and dynamic properties of a large number of surfactants in solution. 

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