Emulsion measuring particle swelling

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. 

Central to any investigation of particle swelling is the use of a reliable method of measuring the size of the particles undergoing expansion. A sedimentation method was described previously (5) which can be used to explore the expansion characteristics of carboxylic emulsion polymers. In the present report, we present a comparison of sedimentation results with those obtained with two... 

By combining thermodynamically-based monomer partitioning relationships for saturation [170] and partial swelling [172] with mass balance equations, Noel et al. [174] proposed a model for saturation and a model for partial swelling that could predict the mole fraction of a specific monomer i in the polymer particles. They showed that the batch emulsion copolymerization behavior predicted by the models presented in this article agreed adequately with experimental results for MA-VAc and MA-Inden (Ind) systems. Karlsson et al. [176] studied the monomer swelling kinetics at 80 °C in Interval III of the seeded emulsion polymerization of isoprene with carboxylated PSt latex particles as the seeds. The authors measured the variation of the isoprene sorption rate into the seed polymer particles with the volume fraction of polymer in the latex particles, and discussed the sorption process of isoprene into the seed polymer particles in Interval III in detail from a thermodynamic point of view. 

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... 

Venkatesan and Silebi [6] used capillary hydrodynamic fractionation to monitor an emulsion polymerisation of styrene monomer as a model system. A sample taken from the reactor at different time intervals is injected into the capillary hydrodynamic fractionation system to follow the evolution of the particle size distribution of the polymer particles formed in the emulsion polymerisation. After the colloidal particles have been fractionated by capillary hydrodynamic fractionation they pass through a photodiode array detector which measures the turbidity at a number of wavelengths instantaneously, thereby enabling the utilisation of turbidimetric methods to determine the particle size distribution. The particle size measurement is not hindered by the presence of monomer-swollen particles. The shrinkage effect due to the monomer swelling phenomenon is found to be accurately reflected in the particle size measurements. 

Other qualitative applications of this type include a study of the differentiation between the intervals of emulsion polymerization [34] and mechanisms of nucleation [35, 36], the swelling of emulsion polymers [37], the partitioning of surfactants [38], and the monitoring of the state of emulsion polymerizations [39]. It has also been demonstrated that particle coagulation could be detected by conductivity measurements [40]. 

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