Investigation of the Interactions of Cationic Polyelectrolytes With Anionic Surfactants: Effects of Polymer, Surfactant and Solution Properties
The intent of this research is to explore and understand the effects that a range of polymer, surfactant and solution parameters have on the interaction of oppositely-charged polymers and surfactants. Cationic polysaccharides were chosen for this research because they are known to interact with anionic surfactants, and they offer a wide range of adjustable polymer properties, including molecular weight, charge substitution, and backbone structure. Cationic poly(vinylpyridinium hydrochloride) polymers were chosen for these studies because they provide the opportunity to explore the effects of charge position on the interaction of cationic polymers with anionic surfactants and how this influences the mechanism of interaction. The overall goal of this research is to define the effects of polymer and surfactant structural properties, and solution properties, on the interaction between cationic polymers and anionic surfactants, and the subsequent formation of coacervate in these systems. The interaction of cationic polymers with varying properties with anionic surfactant was studied using conventional microscopic and macroscopic methodologies to probe the mechanism of interaction in these systems. Polyquaternium-10 systems interacted with anionic surfactant in accordance with the cooperative mechanism of interaction and coacervate formation as described by Goddard. The mechanism of interaction between poly(vinylpyridinium hydrochloride) polymers and anionic surfactant was found to be dependent on the position of the cationic charge relative to the hydrophobic polymer backbone. Polymer-surfactant interaction with poly(4vinylpyridinium hydrochloride) and anionic surfactant occurred via the site-specific cooperative mechanism of interaction. However, the interaction of poly(2-vinylpyridinium hydrochloride) with anionic surfactant exhibited characteristics of the site-specific cooperative interaction mechanism as well as the macroion-macroion interaction mechanism. A high-throughput screening method was developed to facilitate systematic studies of the effects of polymer, surfactant and solution properties on the macroscopic property of coacervate formation. This method allowed rapid and reproducible preparation and analysis of multi-component systems and representation of the amount of coacervate and compositional range of coacervate formation in these systems in easily understood contour phase diagrams. In the cationic polysaccharide systems, the amount of coacervate and the compositional range of coacervate formation displayed a dependence on both the polymer charge density and molecular weight. Also, the polymer critical overlap concentration was observed to affect coacervate amount with higher coacervate formation observed above c*. Coacervate formation with the poly(vinylpyridinium hydrochloride) polymers was found to be dependent not only on the position of the cationic charge on the polymer, but also on the structure of the surfactant tail group. Coacervate formed initially with P4VP and P2VP and sodium capryl sulfonate and sodium xylene sulfonate was not stable over 24 hours, however coacervate formed between these polymers and sodium dodecylbenzene sulfonate was stable over 24 hours. This indicates that a hydrophobic chain with sufficient length and/or an aromatic group is necessary to form thermodynamically stable coacervate. The effect of salt in solution on polymer-surfactant interaction was studied with both classes of polymer. A dependence of coacervate amount and compositional range of coacervate formation on salt concentration was observed. The effect of salt was dependent on the degree of polymer charge substitution. The order of addition of polymer, surfactant, and salt also affected coacervate formation. This was consistent for both low and high molecular weight polymers, as well as low and high charge substituted polymers. Although an effect of addition order was observed in all systems, the specific effects differed depending on the polymer properties.