Latexes characterization methods

The loci and concentration of these functional groups often determine the latex performance in a given application. Therefore, it is important to know the distribution of functional groups between the serum, particle surface, and particle interior as a function of the type and concentration of the functional monomer and the technique of polymerization. Thus characterization methods developed to determine the loci of these functional groups are useful in research to develop new latexes and modifications of older latexes, in development to ensure that the scale-up does not result in a change in the loci of the functional groups, and in production to ensure batch-to-batch uniformity of the product. 

Figure 41.1 shows, for illustrative purposes, the fracto-grams for two different size ranges of polystyrene latex microspheres. (Polystyrene latex standards with narrow size distributions are ideal probes for testing the resolving power and accuracy of particle characterization methods. Those techniques unable to resolve close-lying latex... 

Using this method of latex characterization, we determined the number of sulfate endgroups on the particle surface and inside the... 

Since latex dispersion application properties are related to the surface properties of the latex particles, there is a need for surface characterization of the particles at large. Historically, these types of systems have been applied as model colloids (Hearn et al, 1981) and therefore required well-characterized surfaces but as the sophistication of new coatings increase, the latex particle surfaces become more important from an industrial perspective. In addition to these applications the utilization of latex particles in pharmaceutical and biomedical applications has also contributed to the development of new surface characterization methods. The surface engineering, that is, variations in size, surface charge and surface hydrophobicity, of latex particles as colloidal carriers has been demonstrated to provide opportunities for the site-specific delivery of drugs (Ilium Davis, 1982). Surface... 

El-Aasser, M.S. (1983) Methods of latex cleaning. In G.W. Poehlein, R.H. Ottewill and J.W. Goodwin (eds). Science Technology of Polymer Colloids. Surface Characterization of Latexes. Characterization, Stabilization and Application Properties, Vol. 11, No. 68. Martinus Nijhoff Publishers, The Hauge, p. 422. 

Three generations of latices as characterized by the type of surfactant used in manufacture have been defined (53). The first generation includes latices made with conventional (/) anionic surfactants like fatty acid soaps, alkyl carboxylates, alkyl sulfates, and alkyl sulfonates (54) (2) nonionic surfactants like poly(ethylene oxide) or poly(vinyl alcohol) used to improve freeze—thaw and shear stabiUty and (J) cationic surfactants like amines, nitriles, and other nitrogen bases, rarely used because of incompatibiUty problems. Portiand cement latex modifiers are one example where cationic surfactants are used. Anionic surfactants yield smaller particles than nonionic surfactants (55). Often a combination of anionic surfactants or anionic and nonionic surfactants are used to provide improved stabiUty. The stabilizing abiUty of anionic fatty acid soaps diminishes at lower pH as the soaps revert to their acids. First-generation latices also suffer from the presence of soap on the polymer particles at the end of the polymerization. Steam and vacuum stripping methods are often used to remove the soap and unreacted monomer from the final product (56). 

The determination of adsorption isotherms at liquid-solid interfaces involves a mass balance on the amount of polymer added to the dispersion, which requires the separation of the liquid phase from the particle phase. Centrifugation is often used for this separation, under the assumption that the adsorption-desorption equilibrium does not change during this process. Serum replacement (6) allows the separation of the liquid phase without assumptions as to the configuration of the adsorbed polymer molecules. This method has been used to determine the adsorption isotherms of anionic and nonionic emulsifiers on various types of latex particles (7,8). This paper describes the adsorption of fully and partially hydrolyzed PVA on different-size PS latex particles. PS latex was chosen over polyvinyl acetate (PVAc) latex because of its well-characterized surface PVAc latexes will be studied later. 

Recently, Mitra et al. have prepared chemically crosslinked nanosized gels from different rubber lattices [148,149]. When added in small quantity (2-16 phr), these low moduli deformable gels have been found to influence the mechanical properties of virgin elastomers like NR and SBR considerably. For example, sulfur prevulcanized nanosized SBR latex gels were prepared and characterized using various methods [148]. The morphology of gel-filled NR and SBR systems has been studied... 

Seven polystyrene latexes prepared with persulfate initiator and bicarbonate buffer were characterized to demonstrate the efficacy of this method (6). Three were monodisperse latexes prepared using conventional emulsifiers four were prepared using sodium styrene sulfonate or sodium vinyltoluene sulfonate as canan-omeric emulsifiers. Each latex was subjected to serum replacement with... 

The foregoing methods developed for the preparation and characterization of monodisperse polystyrene latexes to be used as model colloids can also be applied to the characterization of industrial latexes. The recipes used for the preparation of these industrial latexes are complex, and most contain a small amount of a functional monomer, e.g., acrylic acid, 2-sulfoethyl methacrylate, or N-methylolacrylamide. These functional monomers are often predominantly water-soluble, so that their use may have several results (i) the monomer may polymerize in the aqueous phase to form a water-soluble polymer that remains in the serum ... 

A series of monodisperse PMMA latexes was synthesized and characterized with respect to refractive index, percent solids, and solution density. The particle size of each latex was analyzed by several different instrumental methods. The methods used include DCP, SFFF, HDC, Quasielastic Light Scattering (QELS), TEM, and turbidity. 

A dry packed column with porous material was used for the characterization according to size of the PVAc latex samples. The packing employed was CPG (Controlled Pore Glass), 2000 A, 200-400 mesh size. Deionized water with 0.8 gr/lit Aerosol O.T. (dioctyl sodium sulphosuccinate), 0.8 gr/lit sodium nitrate and 0.4 gr/lit sodium azide served as the carrier fluid under a constant flowrate. The sample loop volume was 10 pC A Beckman UV detector operating at 254 nm was connected at the column outlet to monitor particle size. A particle size-mean retention volume calibration curve was constructed from commercially available polystyrene standards. For reasons of comparison, the samples previously characterized by turbidity spectra were also characterized by SEC. A number of injections were repeated to check for the reproducibility of the method. 

The various latexes were characterized with respect to particle size and size distribution, surface charge and functional group density, and electrophoretic mobility behavior. As observed by transmission electron microscopy all latexes were found highly monodisperse with a uniformity ratio between 1.001 and 1.010, a property due to the short duration of the nucleation period involved in the various radical-initiated heterogeneous polymerization processes. The surface charge density was determined by a colorimetric titration method reported elsewhere [13]. 

It must be stressed that the raw curves are not size distributions and calibration is required to convert to absolute values [29]. The importance of the correction for the breakdown in the laws of geometric optics is stressed by Weiner et. al. [30] who show excellent agreement between theoty and experiment when this is done correctly. They also use the Brookhaven disc photocentrifuge to characterize ASTM carbon blacks.[3 i ] This method has been used to characterize void-containing latex particles [32]. Commercial instruments are available from Joyce-l.oebI, CPS Instruments and Brookhaven. 

The sedimentation FFF is shown schematically in Fig. 2a. The separation channel is situated inside a centrifuge rotor and the centrifugal forces are applied radially [8]. The method can be used for the analysis and characterization of various latexes, inorganic particles, emulsions, biological cells, and so forth. The retention parameter A depends on the effective mass of the particles ... 

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