Volume emulsions

Polymers of vinyl acetate are produced commercially in large volumes. Emulsions of poly(vinyl acetate) are used as paint bases, coatings, and adhesives. Overall, the polymerization processes involving vinyl acetate are quite straightforward. 

Emulsion Polymerization (ed. volume) Emulsion Polymerization (ed. volume)... 

The rheological properties of emulsions are influenced by a number of interacting factors, including the nature of the continuous phase, the phase volume ratio, and to a lesser extent, particle size distributions. A variety of products ranging from mobile liquids to thick semisolids can be formulated by altering the dispersed phase volume and/or the nature and concentration of the emulsifiers. For low internal phase volume emulsions, the consistency of the emulsion is generally similar to that of the continuous phase thus. 

Jimenez et al. also used the ICP-MS method for the determination of Al, Ba, Bi, Cd, Co, Cu, Mn, Ni, Pb, Sn, and V. The main differences that they initiated focused on the on-line formation of olive oil-in-water emulsions, the considerable time-gain, and the automatic sample preparation process. Among the various experimental parameters studied and optimized for the development of this method were emulsifier concentration at the mixing point, emulsifier concentration in the carrier solutions in the valves, injected sample emulsifier volumes, emulsion formation flow rate, design of the FIA manifold used (emulsion formation, reactor length, and size of the different connections), and the radiofrequency power in the plasma. 

Figure 14.1 Multifaceted particles of a Tetradecanelwater 77% phase volume emulsion 5 mm = 10 fim...

The upper limit for the number of latex particles per volume emulsion is consequently... 

Figure 9 shows the relaxation time T2 of micelles of sodium dodecyl sulfate (SDS) as a function of SDS concentration [13,16,17], It is evident that the maximum relaxation time of micelles is observed at an SDS concentration of 200 mM. This implies that SDS micelles are most stable at this concentration. For several years researchers at the CSSE have tried to correlate the measured T2 with various equilibrium properties such as surface tension, surface viscosity, and others, but no correlation could be found. However, a strong correlation of t2 with various dynamic processes such as foaming ability, wetting time of textiles, bubble volume, emulsion droplet size, and solubilization of benzene in micellar solution was found [18]. 

Although it is hard to draw a sharp distinction, emulsions and foams are somewhat different from systems normally referred to as colloidal. Thus, whereas ordinary cream is an oil-in-water emulsion, the very fine aqueous suspension of oil droplets that results from the condensation of oily steam is essentially colloidal and is called an oil hydrosol. In this case the oil occupies only a small fraction of the volume of the system, and the particles of oil are small enough that their natural sedimentation rate is so slow that even small thermal convection currents suffice to keep them suspended for a cream, on the other hand, as also is the case for foams, the inner phase constitutes a sizable fraction of the total volume, and the system consists of a network of interfaces that are prevented from collapsing or coalescing by virtue of adsorbed films or electrical repulsions. 

Apart from chemical composition, an important variable in the description of emulsions is the volume fraction, outer phase. For spherical droplets, of radius a, the volume fraction is given by the number density, n, times the spherical volume, 0 = Ava nl2>. It is easy to show that the maximum packing fraction of spheres is 0 = 0.74 (see Problem XIV-2). Many physical properties of emulsions can be characterized by their volume fraction. The viscosity of a dilute suspension of rigid spheres is an example where the Einstein limiting law is [2]... 

The preceding treatment relates primarily to flocculation rates, while the irreversible aging of emulsions involves the coalescence of droplets, the prelude to which is the thinning of the liquid film separating the droplets. Similar theories were developed by Spielman [54] and by Honig and co-workers [55], which added hydrodynamic considerations to basic DLVO theory. A successful experimental test of these equations was made by Bernstein and co-workers [56] (see also Ref. 57). Coalescence leads eventually to separation of bulk oil phase, and a practical measure of emulsion stability is the rate of increase of the volume of this phase, V, as a function of time. A useful equation is... 

The HLB system has made it possible to organize a great deal of rather messy information and to plan fairly efficient systematic approaches to the optimiza-tion of emulsion preparation. If pursued too far, however, the system tends to lose itself in complexities [74]. It is not surprising that HLB numbers are not really additive their effective value depends on what particular oil phase is involved and the emulsion depends on volume fraction. Finally, the host of physical characteristics needed to describe an emulsion cannot be encapsulated by a single HLB number (note Ref. 75). 

Figure Bl.14.13. Derivation of the droplet size distribution in a cream layer of a decane/water emulsion from PGSE data. The inset shows the signal attenuation as a fiinction of the gradient strength for diflfiision weighting recorded at each position (top trace = bottom of cream). A Stokes-based velocity model (solid lines) was fitted to the experimental data (solid circles). The curious horizontal trace in the centre of the plot is due to partial volume filling at the water/cream interface. The droplet size distribution of the emulsion was calculated as a fiinction of height from these NMR data. The most intense narrowest distribution occurs at the base of the cream and the curves proceed logically up tlirough the cream in steps of 0.041 cm. It is concluded from these data that the biggest droplets are found at the top and the smallest at the bottom of tlie cream.

Although the remainder of this contribution will discuss suspensions only, much of the theory and experimental approaches are applicable to emulsions as well (see [2] for a review). Some other colloidal systems are treated elsewhere in this volume. Polymer solutions are an important class—see section C2.1. For surfactant micelles, see section C2.3. The special properties of certain particles at the lower end of the colloidal size range are discussed in section C2.17. 

Finally, add an excess of concentrated hydrochloric acid slowly with stirring to the alkaline filtrate remaining from the original reaction product. As the solution becomes acid, the sulphonyl-aniline separates as a thick sticky syrup which, when stirred, rapidly crystallises. Cool the mixture in ice-water if necessary, and then filter off the solid product at the pump, wash well with water, and drain. Recrystallise from a mixture of 2 volumes of ethanol and i volume of water to prevent the sulphonyl-aniline from separating as an emulsion, allow the hot solution to cool spontaneously (with occasional stirring) until crystallisation starts, and... 

Dichloramine-T. Dilute 80 ml, of freshly prepared 2N sodium hypochlorite soluticMi (preparation, p. 525) with 80 ml. of w ter, and then add with stirring 5 g. of finely powdered toluene-p-sulphonamide, a clear solution being rapidly obtained. Cool in ice-water, and then add about 50 ml. of a mixture of equal volumes of glacial acetic acid and water slowly with stirring until precipitation is complete the dichloro-amide separates at first as a fine emulsion, which rapidly forms brittle colourless crystals. Filter off the latter at the pump, wash well with... 

To 2 ml. of the ester in a test-tube add slightly more than the same volume of a cold saturated aqueous copper acetate solution. The blue colour of the latter turns immediately to a pale green. Now shake the tube vigorously in order to produce an emulsion of the ester in the aqueous layer. Scratch the sides of the tube with a rod, and shake vigorously as before. Crystallisation may be delayed for about 5 minutes, but, when once started, rapidly gives a copious precipitate... 

To separate the oil added an equal volume of fresh cool water (note waited until solution cooled before adding the water). The oil started to drop out perfectly, used DCM to extract all traces of the oil. This woik up is by far the cleanest, easiest and simplest to date... (This dreamer was tried all method of ketone synthesis)... Once the oil was extracted, the extracts were pooled washed with sodium bicarbonate lx, saturated solution of NaCI 1x, and two washes with fresh dHzO... Some time was required for the work up as there was a little emulsion from the use of the base wash and then with the first water wash. The JOC ref suggested using an alumina column to remove the catalyst (could be a better way to go). 

In an emulsion polymerization experiment at 60°C the number of micelles per unit volume is 5.0 X 10 hter and the monomer concentration in the micelle... 

In this example the number of micelles per unit volume is exactly twice the stationary-state free-radical concentration hence the rates are identical. Although the numbers were chosen in this example to produce this result, neither N nor M are unreasonable values in actual emulsion polymerizations. 

Higher alkyl acrylates and alkyl-functional esters are important in copolymer products, in conventional emulsion appHcations for coatings and adhesives, and as reactants in radiation-cured coatings and inks. In general, they are produced in direct or transesterification batch processes (17,101,102) because of their relatively low volume. 

The largest volume of hydrauHc fluids are mineral oils containing additives to meet specific requirements. These fluids comprise over 80% of the world demand (ca 3.6 x 10 L (944 x 10 gal))- In contrast world demand for fire-resistant fluids is only about 5% of the total industrial fluid market. Fire-resistant fluids are classified as high water-base fluids, water-in-oil emulsions, glycols, and phosphate esters. Polyolesters having shear-stable mist suppressant also meet some fire-resistant tests. 

The fluid is formulated from a premium mineral od-base stock that is blended with the required additive to provide antiwear, mst and corrosion resistance, oxidation stabdity, and resistance to bacteria or fungus. The formulated base stock is then emulsified with ca 40% water by volume to the desired viscosity. Unlike od-in-water emulsions the viscosity of this type of fluid is dependent on both the water content, the viscosity of the od, and the type of emulsifier utilized. If the water content of the invert emulsion decreases as a result of evaporation, the viscosity decreases likewise, an increase in water content causes an increase in the apparent viscosity of the invert emulsion at water contents near 50% by volume the fluid may become a viscous gel. A hydrauHc system using a water-in-od emulsion should be kept above the freezing point of water if the water phase does not contain an antifreeze. Even if freezing does not occur at low temperatures, the emulsion may thicken, or break apart with subsequent dysfunction of the hydrauHc system. 

For the most part, additives control the appHcation or theological properties of a paint. These additives include materials for latex paints such as hydroxyethylceUulose, hydrophobicaHy modified alkah-soluble emulsions, and hydrophobicaHy modified ethylene oxide urethanes. Solvent-based alkyd paints typically use castor oil derivatives and attapulgite and bentonite clays. The volume soHds of a paint is an equally important physical property affecting the apphcation and theological properties. Without adequate volume soHds, the desired appHcation and theological properties may be impossible to achieve, no matter how much or many additives are incorporated into the paint. 

Almost all synthetic binders are prepared by an emulsion polymerization process and are suppHed as latexes which consist of 48—52 wt % polymer dispersed in water (101). The largest-volume binder is styrene—butadiene copolymer [9003-55-8] (SBR) latex. Most SBRlatexes are carboxylated, ie, they contain copolymerized acidic monomers. Other latex binders are based on poly(vinyl acetate) [9003-20-7] and on polymers of acrylate esters. Poly(vinyl alcohol) is a water-soluble, synthetic biader which is prepared by the hydrolysis of poly(viayl acetate) (see Latex technology Vinyl polymers). 

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