Latexes particle size measurements

Latex particle size measurements are generally conducted by either light scattering or by elec-... 

Latex particle size measurements are generally conducted by either light scattering or by electron microscopy. Rowell et al. [557] reported rigorous measurements of polystyrene latex particles by both techniques, and the average values agreed within 1%. The preparation for TEM involved the drying of a drop of the... 

PVA and TaM -for the 88%-hydrolyzed PVA. The same dependence was found for the adsorbed layer thickness measured by viscosity and photon correlation spectroscopy. Extension of the adsorption isotherms to higher concentrations gave a second rise in surface concentration, which was attributed to multilayer adsorption and incipient phase separation at the interface. The latex particle size had no effect on the adsorption density however, the thickness of the adsorbed layer increased with increasing particle size, which was attributed to changes in the configuration of the adsorbed polymer molecules. The electrolyte stability of the bare and PVA-covered particles showed that the bare particles coagulated in the primary minimum and the PVA-covered particles flocculated in the secondary minimum and the larger particles were less stable than the smaller particles. 

The adsorbed layer thickness for the llOOnm-size particles could not be measured by photon correlation spectroscopy because of the lOOOnm upper limit of this instrument. Again, the agreement between the two methods is excellent. It is interesting that the adsorbed layer thickness increases with increasing latex particle size and that these values vary with the 0.5 power of the particle radius, i.e., where R is the particle radius. This re-... 

The useful range of the transmission electron microscope for particle size measurement is c. 1 nm-5 p,m diameter. Owing to the complexity of calculating the degree of magnification directly, this is usually determined by calibration using characterised polystyrene latex particles or a diffraction grating. 

The diameter of latex particles was measured from their transmission electron micrographs which were obtained by use of a Hitachi electron microscope HU-12AF. The uniformity ratio of particle size (U) was calculated from eq. 2 ... 

An ICI-Joyce Loebl Disc Centrifuge MK III, a photosedimento-meter, was used to measure the latex particle size distribution. The latex had a unimodal particle size distribution with a diameter of 1.05 micrometers (surface area average). The methods of separating latex particles by a centrifugal field and detecting the size distribution by a photocell may be found in the literature. 

Chang, K., Litt, M., and Jamieson, A. M., "The Measurement of Latex Particle Size by Quasielastic Laser Light Scatter-ing", J. Poly. Sci.-Phys., to be published. 

Latex particle sizes and polydispersity were measured by use of an ICI Joyce Loebl disc centrifuge (JLDC) photosedimentometer (11,12). 

Hopefully, it has become evident that specific turbidity gives consistent and reproducible qualitative results. Two approaches have been used to translate the specific turbidity measurements from the previously mentioned experiments into latex particle size ... 

Also it should be noted that this computerized HDC analysis for particle-size measurements oi these latexes was within 2% oi that measured by TEM. Since the particle-size determinations by the two different methods were in close agreement it was accepted that the HDC eluant composition was minimizing the particle-swelling phenomenon of the carboxylated S/B particles. 

In this paper, a means is demonstrated for experimentally determining the percent of monomer conversion at which soap micelles disappear from the system during emulsion polymerization. By applying the mathematics and latex particle surface area which a soap molecule will occupy, developed for the soap titration particle size measurement procedure, the average particle size of the finished latex can be calculated. In fact, under some circumstances It might even be feasible to adjust monomer content. 

In view of the problems involved with the particle size measurement of soft particles by electron microscopy and the uncertainty In surface coverage by oleate soap molecules which were discussed in the introduction, agreement between the V/S average electron microscope measurements and polymerization rate measurements for these latexes Is quite acceptable. 

The object of this study was to clarify some aspects of the mechanism of shear-induced flocculation in colloidal dispersions. Vinyl chloride homopolymer and copolymer latices were prepared by emulsion polymerization using sodium dodecyl sulphate as emulsifier. Agglomeration behavior in these latices was studied by measuring the mechanical stability using a high speed stirring test. The latex particle size was measured by an analytical centrifuge. Molecular areas of emulsifier in the saturated adsorption layer at the surface of homopolymer and copolymer latex particles were estimated from adsorption titration data. 

The surface activity of these compounds was not studied in detail. As mentioned in the Experimental Section, all were about equivalent in nucleating particles during emulsion polymerization. The resulting latexes when dialyzed to remove excess salt were stable against settling even at 10% solids over many months. Data on samples where both latex particle size and critical micelle concentration were measured is shown in Table II. 

The determination of the distance dependence of the steric repulsion between latex particles by measuring the osmotic pressure of dispersions at different volume fractions was first accomplished by Ottewill and coworkers (Barclay et ai, 1972 Cairns et al., 1976 Ottewill, 1976 1980). The apparatus used to make these measurements is shown in Fig. 13.4. The cell body was cylindrical in shape. Mercury was used as a piston in the cell. The dispersion was layered onto the top of the mercury and its level adjusted until it was just proud of the top of the cell. A millipore filter, of 0-2 pm mean diameter pore size, was placed centrally over the dispersion. A stainless steel top, fitted with a uniform bore capillary, completed the pressure cell. 

In particle size measurements, one of the most inqKatant problems is the obtaining of a representative sample. It is the most difficult problem, and one that is often overlooked or undoestimated, especially for latexes. This problem increases in magnitude as the sample source increases in size, such that it is easier to obtain a representative sample from a 1-litre container than it is to obtain one from a 200-litre drum and, in turn, it is even more difficult to obtain a representative sample from a rail tank car. The reasons for this are obvious when one takes into consideration such factors as agglomeration, flocculation, settling, contamination and so forth. It is sufficient simply to call attention to this problem while collecting a sample for measurement as well as raising this question before measurements are made. 

TEM has proven to be the most effective technique for the characterization of the particle size distribution in emulsions. A dilute solution cast on a carbon film and metal shadowed shows an agglomerate of latex particles in a commonly encountered drying pattern where the shadowing method shows the particles are flat and obviously not separate or discrete (Fig. 5.75A). The area in Fig. 5.75B would also be difficult to use for particle size measurement, whereas in... 

The authors acknowledge gratefully the contributions of J. G. Cobler and Miss C. Kleeman for the ultracentrifuge particle size measurements, E. B. Bradford for the electron microscope particle size measurements. Miss D. L. Dickens, A. S. Teot, and N. Sarkar for the critical coagulation concentration experiments, R. D. Van Dell for the SDS adsorption experiments, the East Main Analytical Laboratory for the osmometric molecular weight and nitrogen adsorption measurements, the Chemical Physics Laboratory for the X-ray fluorescence measurements, and J. B. Shaffer in the preparation of the latexes. 

Dissymmetry of light scattering was used to give a relative measure of the latex particle size before and after ion exchange. 

The number of specimens and the number of features to be measured should also be considered. Statistical parameters, such as the variability and size of features and inherent errors in the analysis, must be taken into consideration. For example, in a typical latex particle size analysis, the number of particles measured must be larger for broader distributions. It is equally important to consider the number of grids and the number of different micrographs used to obtain a random sampling. 

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