Emulsions and Latexes

In this special volume on polymer particles, recent trends and developments in the synthesis of nano- to micron-sized polymer particles by radical polymerization of vinyl monomers in environmentally friendly heterogeneous aqueous and supercritical carbon dioxide fluid media are reviewed by prominent worldwide researchers. Polymer particles are prepared extensively as synthetic emulsions and latexes, which are applied as binders in the industrial fields of paint, paper and inks, and films such as adhesives and coating materials. Considerable attention has recently been directed towards aqueous dispersed systems due to the increased awareness of environmental issues. Moreover, such polymer particles have already been applied to more advanced fields such as bio-, information, and electronic technologies. In addition to the obvious commercial importance of these techniques, it is of fundamental scientific interest to completely elucidate the mechanistic details of macromolecule synthesis in the microreactors that the polymer particles in these heterogeneous systems constitute. 

Polyacrylic thickening agent for aqueous polymer emulsions and latex dispersions backing of plush and carpets improves antistatic properties. 

Johnston KP, Jacobson GB, Lee CT, Meredith C, Da Rocha SRP, Yates MZ, DeGrazia J, Randolph TW. Microemulsions, emulsions, and latexes. In Jessop P, Leitner W, eds. Chemical Synthesis Using Supercritical Fluids. Weinheim, Germany Wiley-VCH, 1999 127-146. 

Figure 11.18 shows the variation of G, G and G" at (/> = 0.57 and o=lHz with % emulsion and latex in the suspoemulsion. The emulsion had much higher moduli than the latex at the same volume fraction. Although the emulsion had a VMD (0.98 tm) that was close to the latex (1.18 pm), the former was much more polydisperse than the latter. The much smaller emulsion droplets present may have accounted for the higher moduli of the emulsion when compared to the latex. As the... 

Johnston, K.P., Jacobson, G.B., Lee, C.T., Meredith, C., Da Rocha, S.R.P., Yates, M.Z., DeGrazia, J., and Randolph, T.W. (1999) Microemulsions, emulsions and latexes. Chemical Synthesis Using Supercritical Fluids, Wiley-VCH Verlag GmbH, Weinheim, Germany, 127-146. 

As compressed carbon dioxide is a nonpolar molecule with weak van der Waals forces (low polarizability per volume), it is a relatively weak solvent [1], Thus, many interesting separations and chemical reactions involving insoluble substances in CO2 can be expected to take place in heterogeneous systems, for example, microemulsions, emulsions, latexes and suspensions. Microemulsion droplets 2-10 nm in diameter are optically transparent and thermodynamically stable, whereas kinetically stable emulsions and latexes in the range from 200 nm to 10 pm are opaque and thermodynamically unstable. 

With recent theoretical and experimental advances in the understanding of colloid and interface science of SCF systems, it is becoming possible to design surfactants for microemulsions, emulsions, and latexes on a rational basis. The-... 

Adenuated total reflectance FTIR (ATR-FTTR) [58] is a mediod vdiere a strongly absorbing medium is placed on one or both sides of a reflective crystal. Because highly absorbing materials can be analysed in this maimer, it is the most commonly used technique for analysing drying films that still contain some water [59,60], and in principle it can even be used to analyse emulsions and latexes. 

It is important to note that die surprising validity of the dilute ECAH theory for moderately concentrated systems has only been demonstrated in systems where the fliennal losses were dominant, such as emulsions and latex systems. In contrast, a solid rutile dispersion exhibits nonlinearity of the attentuation above 10% by volume (Fig. 2). 

There is another approach to acoustics which employs a short-wave requirement. It was introduced by Riebel et al. (20). This approach works only for large particles (above 10 um, but requires only limited input data on the sample. The theory may provide an important advantage in the case of emulsions and latex systems when the thermal expansion is not known. 

Uses Suspending agent for pigments and fillers in water-based paints, inks, or other coatings, and the abrasive particles in waxes or polishes vise, modifier for emulsion and latex compds. binder for textiles thickener... 

Uses Defoamer for water-reducible emulsion and latex systems, high gloss architectural paints, wood preservative stains, aq. flexographic inks, primers, acid catalyzed systems, automotive basecoats, coating colors (folding boxboard), wastewater treatment Properties Lt. yel. si. vise, translucent liq. sol. in butanol, glycol ethers, ethoxypropanol, hexanol, isobutanol, IPA, methoxypropanol, MEK, min. spirits, xylene partly sol. in acetone, ethanol dens. 1.01 g/ml (20 C) flash pt. > 200 C pH = 7.0 (2% in Dl water) nonionic 100% act. 

Chem. Descrip. Blend of surface-act. components/polysiloxane adduct Uses Defoamer, air release agent tor water-sol. industrial coatings (acrylics, alkyds, HC, NC, PU emulsions and latexes, water-reducible alkyds, acrylics, polyesters, epoxy esters)... 

Chem. Descrip. Fully hydrolyzed PVAL, 99-99.8% hydrolysis CAS 9002-89-5 EINECS/ELINCS 209-183-3 Uses Film-former, binder in adhesives, paper, paperboard sizing and coatings, textiles, films, building prods. strength additive for concrete, cement binder for pigments, ceramics, cements, plastics, particleboard oil/solv. barrier props, in hoses, gaskets, pipes carrier for optical bright-eners cosmetic and personal care incl. face masks emulsifier in emulsions and latexes... 

The unique density dependence of fluid properties makes supercritical fluids attractive as solvents for colloids including microemulsions, emulsions, and latexes, as discussed in recent reviews[l-4]. The first generation of research involving colloids in supercritical fluids addressed water-in-alkane microemulsions, for fluids such as ethane and propane[2, 5]. The effect of pressure on the droplet size, interdroplet interactions[2] and partitioning of the surfactant between phases was determined experimentally[5] and with a lattice fluid self-consistent field theory[6]. The theory was also used to understand how grafted chains provide steric stabilization of emulsions and latexes. 

In this paper we review principles relevant to colloids in supercritical fluids colloids in liquids are discussed elsewhere [24]. Thermodynamically unstable emulsions and latexes in CO2 require some form of stabilization to maintain particle dispersion and prevent flocculation. Flocculation may be caused by interparticle van der Waals dispersion forces (Hamaker forces). In many of the applications mentioned above, flocculation of the dispersed phase is prevented via steric stabilization with surfactants, in many cases polymeric surfactants. When stabilized particles collide, polymers attached to the surface impart a repulsive force, due to the entropy lost when the polymer tails overlap. The solvent in the interface between the particles also affects the sign and range of the interaction force, and the effect of solvent is particularly important for highly compressible supercritical solvents. Since the dielectric constant of supercritical CO2 and alkanes is low, electrostatic stabilization is not feasible [24] and is not discussed here. For lyophobic emulsion and latex particles (-1 xm), the repulsive... 

It is important to note that the UCSD above is for the actual finite molecular weight stabilizer, not an infinite molecular weight stabilizer (theta density). Many experimental stability studies of emulsions and latexes in liquid solvents indicate a correlation between the critical flocculation temperature and the theta temperature, 7 0.[68]. However, the difference between Tq and the UCST is often only a few degrees... 

This comprehensive article, the third of a series, supplies a description of colloid fundamentals of emulsions and latexes. Information is included on their technical characteristics and their behaviour in technological processes, which are closely dependent on their colloid stability. The article provides the main colloid concepts useful in the technology and formulation of resin emulsions, polymer latexes and emulsion paints. 17 refs. ISRAEL... 

Aldehyde-releasing agents, particularly those which release formaldehyde, find application in a number of processes as preservatives, such as in cutting-oil emulsions and latexes [325]. Formaldehyde may be applied to natural keratin fibres in the leather and textile industry to prevent problems of anthrax contamination [341], in paints as preservatives [342] and in the construction industry as toxic washes to prevent microbial growth on large surface areas [343] or as additives in concrete itself [344]. Formaldehyde has long been used as a preservative for natural history specimens in, for example, museums, to prevent biodeterioration and maintain the structure of organs and tissues [345]. 

The major structural unit of interest in emulsions, microemulsions, colloids and latexes is the particle. It is well known that the particle shape, size and distribution of a latex controls the properties and end use applications. Many latexes are manufactured with a controlled and sometimes monodisperse distribution of particle sizes. Polymer liquids, in the form of emulsions and adhesives, are wet and sticky, and therefore specimen preparation for electron microscopy is very difficxilt. As a result of the importance of the determination of particle size distribution, microscopy techniques have focused on specimen preparations which do not alter this distribution or which alter it as little as possible. Methods have included special cryotechniques (Section 4.9), staining-fixation methods (Section 4.4), microtomy (Section 4.3) and some simple methods (Section 4.1) such as dropping a solution onto a specimen holder. This section is meant to provide a brief survey of the types of microscopy applications which have been foimd useful in the evaluation of emulsions and latexes. 

The values of Rp varied with the 1.0 power of emulsifier concentration and the 2.0 power of initiator concentration. The values of N varied with the 3.7 power of emulsifier concentration and 0.3 power of initiator concentration. These variations were unusual, and transmission electron microscopic examination of the inverse emulsions and latexes showed that some appeared to be multiple emulsions, i.e., possibly 10-50nm droplets of oil dispersed in 100-300nm droplets of water dispersed in the continuous o-xylene phase. 

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