Displacement of amphiphilic block copolymers from dispersed nanoparticles
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Interfacial interactions are responsible for many of the special properties sought after in composite materials. Adsorption between molecule and particle in solvent based processing is an excellent example of such interactions. Control over adsorption is responsible for rheology, stabilization, and other properties. Manipulating adsorption is an exercise in influencing system entropy and enthalpy. Our group has studied the adsorption of poly(ethylene oxide) – poly(propylene oxide) – poly(ethylene oxide) block copolymer upon protonated silica surfaces. It has been shown that these amphiphilic polymers will adsorb to silica nanoparticles, and above a solvent-dependent critical concentration, will form micelle-like aggregates on the particle surfaces. Recently we have studied the use of molecular additives as displacers in aqueous, Pluronic-containing nanoparticle dispersions. This includes the use of small, polar organic molecules, which we have shown to completely displace Pluronic from the silica surface. Following in line with this work, the study of PEO homopolymer and divalent salts has been pursued. These additives have been well studied, but the use of them as displacers has not. Not only are they powerful in regard to this use, but they are low-cost also, presenting true opportunities to large scale, solvent based processing of composite materials. Chapter 1 of this document covers a brief introduction in the importance of molecular adsorption. Some theoretical and experimental results a reviewed that are pertinent to the subject matter. Chapter 2 presents results on the use of PEO homopolymer as a displacer for Pluronic P105 in an aqueous system containing dispersed protonated silica nanoparticles. An introduction to the surfactant and some general trends regarding its behavior can be found here. Also discussed are the methods used to probe the action of PEO displacers, and the results obtained. Chapter 3 discusses the role of divalent salts as displacers are explained. An introduction to the surfactant is again given, as are the experimental methods used. Results obtained on the action of the divalent salts are divulged and explained.