Polyelectrolyte gels, namely poly(acrylic acid) (PAA), synthesized in the presence of high-molarity salts or ionic liquids exhibit fascinating behaviors that are much different from PAA gels synthesized without salt, even when the latter are incubated in high-molarity salt solutions. The most prominent feature of these materials is a marked enhancement in mechanical strength and high elongation, with near-complete recovery. The enhanced mechanical properties of these high salt-loaded gels significantly diminish upon washing the materials with water to remove the salt, and cannot be restored upon incubation in solutions containing equivalent concentrations of salt, indicating that the addition of salts or ionic liquids during synthesis is critical to property enhancement. This enhanced elasticity is thought to be brought about by phase-separated regions of salt acting as a plasticizer and modulating intermolecular interactions between AA units. As no base is employed during or after synthesis to neutralize AA units, the gels are believed to be substantially unionized, leading to unique polymer-polymer and polymer-solvent interactions when in the presence of salt.<br/><br/>This study focused on the addition of a wide variety of salts during synthesis, including chloride salts of cobalt, zinc, lithium, rubidium, and sodium. Besides chloride salts, carbonate, nitrate, sulfate, and bromide salts, as well as ionic liquids, have been studied. In addition to characterizing the changes exhibited by these materials, this phase of the project has focused on analyzing the structure of these materials and to understand the cause of the enhanced properties. Techniques such as x-ray scattering, including x-ray absorption fine structure (XAFS), neutron scattering, and atomic force microscopy have been used to probe these systems to develop a more complete understanding of the unique molecular interactions that they exhibit.

Enhanced elasticity and property modification of poly(acrylic acid) and other polyelectrolytes: Studying and modeling the effects of salts and ionic liquids added during synthesis on material behavior

255th National Meeting (2018)

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