Aqueous Emulsifier Solutions

We will first discuss the modeling of the second stage of emulsion polymerization, because most of the polymerization occurs in this stage. One of the simplest (and oldest) models existing is that of Smith and Ewart. This model was the first to explain gross experimental observations. It may be added that the Smith and Ewart theory assumes that primary radicals (SO4 ) can enter into the polymer particles. Although we have already explained that this is not possible because of thermodynamic constraints, it is an important simplifying assumption of this theory. 

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In semisolid emulsions, excess cetyl alcohol combines with the aqueous emulsifier solution to form a viscoelastic continuous phase that imparts semisolid properties to the emulsion and also prevents droplet coalescence. Therefore, cetyl alcohol is sometimes referred to as a consistency improver or a bodying agent , although it may be necessary to mix cetyl alcohol with a hydrophilic emulsifier to impart this property. 

The rate of polymerization was reported to increase with increasing weight ratio water/monomer. This shows that the water-phase polymerization becomes important. The higher the amount of VC that is dissolved in water, the higher is the rate of polymerization observed [87]. The rate of water-phase polymerization was found to be proportional to the monomer saturation degree of the aqueous emulsifier solution [87]. 

A latex modified asphalt emulsion can be prepared using several methods addition of the latex in the aqueous emulsifier solution, direct injection in the asphalt hne just ahead of the coUoid mill or post-addition to the pre-manufactured emulsion, as schematically shown in Fig. 12-9. Addition to the aqueous phase is the most commonly used method. The direct injection process often helps to produce an emulsion with a desired high viscosity for chip seal application (Sect. 12.3.1). This is due to the narrow particle size distribution of the asphalt emulsion produced with this process. 

The inverse emulsion form is made by emulsifying an aqueous monomer solution in a light hydrocarbon oil to form an oil-continuous emulsion stabilized by a surfactant system (21). This is polymerized to form an emulsion of aqueous polymer particle ranging in size from 1.0 to about 10 pm dispersed in oil. By addition of appropriate surfactants, the emulsion is made self-inverting, which means that when it is added to water with agitation, the oil is emulsified and the polymer goes into solution in a few minutes. Alternatively, a surfactant can be added to the water before addition of the inverse polymer emulsion (see Emulsions). 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

The reactor is loaded with a solution of emulsifier in an organic solvent and the aqueous monomer solution (20-60%) is dispersed in the organic phase by stirring. The obtained emulsion is deoxygenated by purging dry nitrogen or by multiple evacuation and thermostated at 30-60°C. Then, an initiator solution is introduced in the reaction mixture and the process is carried out at 30-60°C for 3-6 h, after which the reaction mixture is aged for 1-5 h. 

Levonantradol (8.4) was synthesized with the intention to introduce a basic amino function into the heterocycle in the hope of obtaining water-soluble salts. Although the solubility of the hydrochloride is not good it was possible to get stable aqueous micellar solutions with the aid of emulsifiers [145] and the compound made its way as an injectable into clinical trials, but never was approved. 

Average treatment volume was 600 gallons. All fluids contained 1% (by volume) of water wetting non-emulsifier. The treatments utilizing a cationic organic polymer included the polymer in all aqueous based fluids. The reported polymer concentration of one percent by volume of the aqueous polymer solution as supplied. Active polymer concentration is actually less than this. When the clay stabilization polymer was part of the well treatment, a non-ionic water wetting nonemulsifier was used. 

Palfray and Sabetay246 added an emulsifying agent, Gardinal, to aid in the oxidation of the water-insoluble 1-0-benzylglyceritol. Aqueous solutions of methanol,247 248 ethanol,13 - 249-261 dioxane,74 - 262 266 acetic acid,230 - 266 and acetic acid buffered with lithium acetate164 have been used. The use of lithium periodate or triethylammonium periodate in aqueous alcohol solution has been suggested,267 because of the solubility of these salts in this medium. 

The QPVP-Cu complex, which is an emulsifier, catalyzed the emulsion polymerization of XOH152. An aqueous solution of the QPVP-Cu complex and a benzene solution of XOH were mixed and stirred, then the system was emulsified and polymerization occurred. After polymerization, the reaction mixture could be separated into two layers, the aqueous catalyst solution, and the benzene solution containing the PPO polymer. The recovered catalyst solution could be used repeatedly. Polymerization was influenced by the pH value of the aqueous catalyst phase. Below pH 7 the main product was biphenoquinone and at pH 8—10 it was PPO. 

Latex Preparation Analysis. Deionized water was used for the aqueous phase in the polymerization and commercial grade vinyl chloride monomer (99.9% pure) was used without further purification. The emulsifier was a salt of a sulfated fatty alcohol, and the emulsifier solution for metering was prepared to have 0.15 mol/L in water. The initiator system was a water soluble redox system. 

The concentration of formation of black spots in emulsion films is close to the emulsifier concentration at which it is possible to disperse a small quantity of the organic phase in certain volume of the aqueous surfactant solution under definite conditions resulting in formation of stable emulsions. Kruglyakov et. al. [510] have compared the concentration of black spot formation in emulsion aqueous films and the minimum surfactant concentration Cmin needed to form stable heptane aqueous emulsion studying the NaDoS emulsifying ability vs. its concentration in the solution. They found that Cmin = 4.110 4 mol dm 3 in a solution containing 51 O 2 mol dm 3 NaCl and Cw = 3.5-4-10 4 mol dm 3, depending on the time of film formation. 

The start-up procedures are as follows. The reaction vessel was charged with the desired amounts of purified water, emulsifier and monomer, and the dissolved oxygen was removed by bubbling purified nitrogen gas through the reaction mixture for at least half an hour. The aqueous initiator solution previously deoxygenated with the nitrogen gas was then fed to the reaction vessel and the polymerization reaction was started. In all cases the reaction tem-perattire was maintained at 50 0.5 C by means of a thennostatted... 

This is supported by the values for the interfacial tension (du Nuoy ring method), 0 0.01 dyne per cm., of a 20% aqueous monomer solution in contact with xylene solutions of emulsifier (0.033, 0.083, and 0.125 gram per cu. cm.). This very low interfacial tension is consistent with the formation of very fine emulsion droplets. 

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