Large-particle size monodisperse latexes

Vanderhoff et al. prepared large-particle size monodisperse latexes on the Space Shuttle (55). These latexes were made from large colloidal droplets consisting primarily of monomers that were polymerized. Droplets of similar size could not be maintained on the ground for sufficient duration due to sedimentation. 

Prior to the measurements of the different reactor latex samples the computerized HDC was calibrated for particle-size using the standard procedure (3) and also for particle-size distribution quantification. For the particle-size distribution calibration two different particle-size monodisperse carboxylated S/B latexes were polymerized. Various mixtures of these latexes were prepared by blending the large 2100A and the small 700A latexes in different ratios by weight 60/40, 70/30, 80/20 and 90/100 respectively. 

Ha et al. [93,94] prepared monodisperse polymer microspheres from 1 to 40 pm in diameter for medical diagnostic tests, as chromatography column packing and as calibration standards. The work deals with the synthesis of large and uniform poly (butadiene-styrene) latex. The ceramic SPG membrane, with a pore diameter of 1.6 pm, was employed. The uniform particle sizes were in the diameter range of 4-6 pm. 

The particle-sizes and particle-size distribution of the two monodisperse carboxylated S/B latexes are shown in the hydrodynamic chromatograms of Figure 1. The average diameters of the large, Df, and the small, Dg, relatively monodisperse latexes were 2100A and 720Arespectively. 

In the seeded emulsion polymerization of some monomers —e.g., styrene—it is possible to obtain final latexes with uniform, large particles by adjusting, during polymerization, the quantity of added emulsifier the formation of new particles is prevented by the limited amount of emulsifier. For vinyl chloride, limited emulsifier is not sufficient to prevent the formation of new particles in fact, to obtain a monodispersed latex, the surface of the particles seeded in a given water volume must be controlled. It is assumed that the growth of new nuclei is related either to the rate of formation of primary useful radicals or to the rate that these are taken by the surface of sized particles. 

No explanation has been offered as to why particular emulsifier mixtures produce monodisperse latexes. Latexes produced by emulsifier-ffee emulsion polymerization are monodisperse (although comparatively large in size). Hence it may be inferred that the coalescence rate should be at a maximum for minimal polydispersity. The emulsifier mixture which produces a monodisperse latex is that which is least effective in stabilizing the particles. 

The normal distribution function is rarely used to describe aerosol particle size distributions because most aerosols exhibit a skewed (long tail at large sizes) distribution function. The normal distribution is, of course, synunetrical. It can be applied to monodisperse test aerosols, to certain pollens and spores, and to specially prepared polystyrene latex spheres. The number frequency function is given by... 

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