Binding of electrically charged submolecular groups (ions) to polymers commonly occurs with charged polymers in water solution to produce ion-polymer complexes due to strong electrostatic interactions. In some cases ions can also bind with uncharged polymers in non-water-based media to greatly modify the structure and material properties of the polymers. For instance, poly(ethylene oxide) (PEO), an uncharged water-soluble polymer with extensive commercial applications, can dissolve salts, such as lithium chloride, in non-aqueous solvents to produce PEO-ion complex with high ion conductivity as solid polymer electrolyte for Li-ion rechargeable battery applications. Despite enormous technical implications of ion binding with neutral polymers the charging mechanism of neutral polymers in organic solvents and in the solid state remains poorly understood. This project aims to control and quantify the electrical charge density and complex formation of PEO polymers with inorganic nanometer-sized ions (macroions) of varied electrical charges and concentration by ultrafast laser spectroscopic methods. With this knowledge, ion-containing polymers with enhanced mechanical and ion transport properties can be developed (including earth-abundant or conventional synthetic polymers in various solvents and in the solid state) into novel functional materials that may be relevant for energy and environmental aspects. This project also combines multifaceted STEM education, where classroom and video demonstrations and hand-on experiences will be developed to engage graduate, undergraduate, and high-school students in fundamental materials design and advanced materials-characterization tools. Broader impacts of this project will also include the recruitment, retention, and mentoring of underrepresented students, including women students, in the STEM fields.
Ion-polymer complexes are commonly formed between ions and charged polymers or polyelectrolytes in aqueous solution due to strong electrostatic interaction. However, electrical charges can be also introduced to neutral polymers, such as poly(ethylene oxide) (PEO), upon ion binding in non-aqueous solvents and in the solid state, resulting in unusual polyelectrolyte-like behaviors of the neutral polymers. This is a much less studied area, and this project aims to elucidate the process of effectively charging neutral polymers by multivalent macroions, leading to the formation of polymer-macroion complexes with enhanced solid-like mechanical strength and fast ion transport. In particular, the electric potential and complex formation of PEO polymers upon binding with hydrophilic inorganic macroions of varied multi-valence and concentration will be quantified by ultrafast laser spectroscopy to fundamentally understand the electrical charging process of neutral polymers in organic solvents and the solid state. The relationship among phase structure, viscoelasticity, and ion conductivity of PEO-macroion complexes will be established and exploited to enhance the mechanical strength and ion transport of the complexes with optimal macroion content. The success of this project could have implications toward a versatile and sustainable material process of earth-abundant or conventional synthetic neutral polymers into advanced functional ion-containing polymers with enhanced ion transport and mechanical integrity.
