Swelling measuring particle

Techniques for Measuring Particle Swelling of Carboxylic Emulsion Polymers... 

The results are generally consistent with a broader treatment of the techniques for measuring particle swelling of carboxylic emulsion polymer latexes reported elsewhere in this Monograph (9). The broader study, which was carried out independently but concurrently, has shown that the magnitude and pH of maximum expansion depends on dilution and ionic strength. Studies of the concentration dependence in the dilute regime and more concentrated systems are underway. 

This relation has been tested by Morton, who determined values of and y from equilibrium swelling measurements of polystyrene latices. The results obtained were in good agreement with values of and y (54) determined by other methods. Allen (J) measured the swelling of natural rubber latex with methyl methacrylate and found the dependence of swelling on particle size to agree well with the above equation. 

Equation 11 refers to equilibrium swelling conditions. Now, Flory (24) concludes from theoretical considerations that monomer is easily supplied to the polymer particles at the required rate even in the case of monomers which are little soluble in water, such as styrene. That equilibrium swelling is maintained during emulsion polymerization is supported by a comparison of values of the monomer concentrations determined in equilibrium swelling measurements with those found to prevail during polymerization and determined by analysis of reaction kinetics (see below). The results obtained by both methods are plotted in Figure 10. 

Values for the propagation rate constant can be determined from bulk or solution experiments. Values of k have been published for a wide variety of monomers as a function of temperature. With standard emulsion polymerization recipes the value of [M]p is determined from equilibrium swelling measurements if a free monomer phase is present and by a mass balance if all the monomer is in the polymer particles. One normally assumes that [M] is not dependent on particle size in latexes comprised of different-sized particles. This assumption will be questionable in some systems, especially those involving high-swelling particles. 

Swelling measurements were used to determine the extent of cross-linking of latex particles which had been prepared by emulsion polymerisation. Two latexes were investigated, a polybutyl acrylate and a polyisodecyl acrylate. With the latter, a comparison was made between the swelling behaviour of the fully crosslinked material... 

Recently an improvement of the microscopic method for evaluating the swelling characteristics of tablet disintegrants has been proposed authors also considered the changes in particle shape that may take place upon swelling.All the microscopic methods, however, present some limitations in their applicability to routine swelling measurements, especially when irregularly shaped materials or materials characterized by small variations of the particle linear dimensions are considered. 

Therefore, although the Coulter Counter method allows an accurate evaluation of particle volume diameter in inert media as checked by mass balance evaluation, in some cases it is not suitable to measure particle swelling. In these cases, the Coulter Counter method needs to be integrated with other granulometric techniques. 

Similar results were obtained with the light blockage method (HIAC), whose inadequacy for swelling measurements can be explained by too small a difference in refractive index between aqueous medium and swollen particles. ... 

It is well known that swelling of resins increases the particle radius. When resin beads are immersed in the solution, water uptake takes place almost immediately, resulting in a new swollen radius. The swollen radius is inversely proportional to the initial solution concentration (Hellferich, 1962). This effect has not been taken into account in the original model of Levenspiel (1972). However, the actual swollen radius of the resin should be used in the model equations, and so measurements should be performed in order to estimate this radius. 

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