Non-equilibrium particle morphology development in seeded emulsion polymerization. 1: penetration of monomer and radicals as a function of monomer feed rate during second stage polymerization (original) (raw)
1999, Colloids and Surfaces A: Physicochemical and Engineering Aspects
https://doi.org/10.1016/S0927-7757(98)00449-X
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Abstract
. A: Physiochemical and Engineering Aspects 153 1999 255᎐270 Non-equilibrium particle morphology development in seeded emulsion polymerization. 1: penetration of monomer and radicals as a function of monomer feed rate during second stage polymerization
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Microemulsions are macroscopically isotropic mixtures of at least three components: water, oil and surfactant. They are single thermodynamically stable phases, different from ordinary emulsions (chapter 8). Microscopically, the surfactant molecules form an extended interfacial monolayer separating the water from the oil molecules. The preferential adsorption of the surfactant reduces the interfacial tension between the polar and non-polar solvent effectively to zero, which, in turn, permits thermal energy to disperse the two incompatible solvents into each other. The general features of the phase behaviour of microemulsions are best introduced by considering the following simple experiment. A simple experiment: We take a test tube with equal amounts of water and oil. As water and oil do not mix, we see two phases, water (A) forming the bottom phase, oil (B) forming the phase on top. This situation is shown by the test tube furthest on the left in fig. 5.1. When we add a surfactant, it has, in principle, three options. It can dissolve in the water phase (fig. 5.1, tube I), it can dissolve In the oil phase (fig. 5.1, tube II) or it can make up its own phase (fig. 5.1, tube III). These situations are frequently observed and are denoted by the three Winsor states (I, II, III), after Winsor, who was the first to study this behaviour systematically ^\ The surfactant rich phase is called the microemulsion. We will explain further how to select the components to achieve a desired microemulsion type, which structures and properties to expect and provide hints for applications of microemulsions. As illustrated in fig. 5.1, the first observation dealing with mixtures of water, oil and surfactant is the spontaneous appearance of different phases. Therefore studying the phase behaviour and the construction of phase diagrams is the first step. A phase diagram may be viewed as the road map for the researcher and helps him to reach his destination or goal. For example, the Gibbs triangle on the left-hand side of fig. 5.1 indicates that at intermediate temperatures a hydrophilic surfactant system is over wide composition regions in the Winsor I (2)-state. The Gibbs triangle on the right-' PA. Winsor, Solvent Properties of Amphiphilic Compounds, Butherworth & Co. (1954).
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The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
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The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
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we have explained the development of composite particle morphologies produced by seeded emulsion polymerization in terms of the ability of second stage polymer radicals to diffuse into, or "penetrate," the seed particles. This has been quantified (Stubbs et al., ibid) by calculating so-called "fractional penetration" values for the second-stage radicals. In this article the effect of the second-stage initiator type, specifically nonionic vs ionic initiators, on particle morphology is investigated. The question to be answered is whether charged (ionic) end groups (from the initiator) on second stage polymer chains "anchor" to the particle surface, making it more likely to form core-shell morphologies. This is investigated by using a poly(methyl acrylate-co-methyl methacrylate)
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