Understanding the Effects of Sheet Size and Salt Addition on Aqueous MXene Dispersions: Phase Behavior, Rheological Properties, and Printability

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MXenes are a family of two-dimensional (2D) crystalline nanomaterials composed of transition metal carbides, nitrides, or carbonitrides. They are very promising for applications in electronics and energy storage devices such as better batteries. One advantage of MXenes is that they can be dispersed in water and processed into devices and structures using fluid phase processing techniques such as direct ink writing (DIW). So far, advances in MXene processing have required time consuming and expensive trial and error approaches. A fundamental understanding of MXene dispersions is needed to consistently achieve functional MXene devices via fluid-based manufacturing methods. This project will address this need by developing a fundamental understanding of the connections between MXene dispersion properties, DIW printing, and the microstructure and electrical conductivity of printed devices. In addition, by considering MXenes as an example of a charged 2D colloidal platelet, this research will also extend the current scientific understanding of dispersions of 2D materials. The research team will collaborate with other researchers on advancing the experimental and theoretical methods to study colloidal dispersions of 2D materials. Undergraduate researchers will be an integral part of the research team, and the PIs will mentor high school students on related research. To further engage K-12 students, the team will develop activities on printing and electrical devices for several programs at Auburn University, including Engineering Day, Promoting Engineering for Kids (PEAK), Women in Engineering Camp, and a Summer Bridge Program for incoming minority engineering students. The proposed research is motivated by the hypothesis that MXene dispersions exhibit a rich phase behavior similar to that of other charged colloidal 2D platelets (also termed disks or plates). The proposed research seeks to answer three questions about MXene dispersions: 1) What are the effects of sheet size distribution on phase behavior and rheology; 2) What are the effects of sodium chloride (NaCl) addition on phase behavior and rheology; and 3) How do dispersion properties affect printability and the electrical conductivity of test structures? This research will advance understanding of MXene phase behavior and the composition and microstructure dependent rheological properties that affect printability. Collaborations with an expert in combining rheology and small angle neutron scattering (Rheo-SANS) and a leader in the development of theories for understanding dispersions of charged 2D materials will increase the depth of scientific understanding. Together these contributions will advance understanding of structure-process-property relationships and how to formulate MXene inks for DIW.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.