Latex swelling behavior

Figure 5 shows the swelling behavior of the model acrylic latexes as determined by photon correlation spectroscopy. Changes in particle diameter are shown instead of radius as in Figures 3 and 4. The diameter, d, at each pH was divided by the initial diameter, d0, determined at pH = 5 (unexpanded). In general shape, the curves are similar to those determined by sedimentation and viscometry. The initial points occurred at a higher pH due to the much lower particle concentration. No effort was made to lower the initial pH with acid consequently, the undesirable salt effect was avoided. 

This microscopic difference in the copolymer composition could influence the particle morphology, especially the distribution of the carboxyl groups within the latex particle, which in turn could be expected to influence the alkali-swelling behavior. 

If the swelling behavior of carboxylated latexes could be characterized only by the increase in the volume fraction, i.e., in particle size, Eq. 1 would still hold but this is not the case in carboxylated latexes. The latex particles are swelled to a great extent, and the polymer segments are dissolved into the aqueous phase and interact between the particles by the hydrogen bonds and chain entanglements. Thus, Eq. 1 is not expected to hold at all and the interparticle interactions are expected to be dominant in the viscosity development of the latex. 

Nishida, S., "Preparation, Characterization and Alkali-Swelling Behavior of Carboxylated Latexes", Ph.D. Dissertation, Lehigh University, 1980. 

In the industrial production of structured AN-Bu-St (ABS) latex particles, the grafting copolymerization of AN and St on crossUnked polybutadiene (PB) seed latex is carried out in emulsion polymerization. Therefore, information on the effect of PB crosslinking density on the swelling of PB latex particles by a St-AN monomer mixture is very important for the production of ABS copolymers with desired properties. Mathew et al. [177] studied the effect of several thermodynamic parameters, such as the crosslinking density, particle size and monomer mixture composition on the swelling behavior of PB latex particles by pure St and AN, and St-AN mixtures of various compositions. They reported... 

The group of Gu Z. in the 2009, reported the behavior of styrene butadiene/ rubber/organo-bentonite nanocomposite prepared from latex dispersion, content was lower than 12 mass%. The results showed were that presence of organo-bentonite in the nanocoposite affects direct in the thermo stability, mechanical properties and swelling behavior, which was attribute to the good barrier properties of the dispersed nanoparticles. The dispersion is an important factor that can affect various properties such as thermal stability [81]. 

From the above Results and Discussion, one could speculate the following scheme given in Figure 14, of alkali-swelling and/ or dissolving behaviors of the MMA-MAA carboxylated latexes. 

Figure 14. Schematic explanation of alkali-swelling and/or dissolving behaviors of carboxylated MMA-MAA copolymer latexes...

To explain the fact that HSPAN swells in water to form gel sheets or macroparticles rather than disintegrating into a gel dispersion, we initially felt that chemical bonding must take place between individual particles of water-swollen gel as water evaporates. Although we cannot totally eliminate this possibility, the proposal of primary chemical bonding is not necessary to explain the behavior of these films and conglomerates. For example, Voyutskii (19) has reviewed the formation of films from vulcanized rubber latexes and concludes that film formation in these systems is observed because of interdiffusion of ends of individual macromolecules in adjacent latex particles. This diffusion can take place even though individual latex particles are crosslinked, 3-dimensional networks and the continuity of the resulting films, even when... 

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. 

The thickening mechanisms of linear carboxyl-containing emulsion polymers have been studied in considerable detail. The polymer molecules of AST emulsions are initially in a coiled configuration within individual latex particles of submicrometer size, and the viscosity of the diluted latex emulsion is similar to that of water prior to neutralization. On the addition of base, the carboxyl groups are ionized, and hydrophilic polymer is formed within the particles. Depending on various factors, which will be elaborated on later in this chapter under the section entitled Factors Affecting the Swelling Dissolution Behavior of Conventional ASTs , the particles may only swell or dissolve completely, or the surface polymer may dissolve and leave swollen cores. 

Amongst the above mentioned compatibilization methods, the obtaining of IPNs and SIPNs often proved to be a promising and very efficient route. An IPN is a polymer alloy comprised of two or more chemically crosslinked polymers. The difference between polymer blends and IPNs is that the latter ones swell instead of dissolving in solvents and do not creep or flow. Types of IPNs include sequential, simultaneous, latex and gradient IPNs and may also be thermoplastic (i.e. when physical crosslinks are imphed). Thermoplastic IPNs behave as thermosets at ambient temperature, but usually flow when heated at certain temperatures, possess IPN properties and often exhibit dual phase behavior [1]. 

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