(2q) Ion-Mediated Manufacturing of Dynamic Nanostructured Polymer Materials

Nanostructured and functionalized polymers are promising for applications in, e.g., photonic devices, surface modifiers, and ionic conductors. Block copolymer (BCP) can self-assemble into various microstructures, resulting from enthalpic interactions and chain stretching entropy. However, the morphology and length scale are sensitive to polymer composition, architecture, and molecular weight, so fabricating periodically oriented, ordered BCP nanostructures with precisely tunable domain size remains a challenge and requires substantial synthetic efforts. In the late 1980s, the development of supramolecular chemistry suggested an alternative way to construct polymers based on non-covalent association of small-molecule “stickers”. The rational design of associating groups can achieve controllable bonding-unbonding reversibility. This “synthesis during use” strategy opens design space for nanostructured polymer blends with various controllable properties while bypassing synthetic challenges. Among various non-covalent interactions, ionic interaction stands out due to the high bond energy approaching covalent bond, flexibility in chemistry, and tunability by temperature, material permittivity, and external fields. More importantly, electrostatic interactions can act over a wider breadth of length scales compared to hydrogen bonds to realize long-range order. Such ionic associating polymers have potential applications, e.g., Li-ion batteries and stimuli-responsive/self-healing coatings due to the dynamic nature of the ionic bonds, and may serve as a compatibilizer in the plastic waste industry. However, the structure-property relationship and chain dynamics have yet to be elucidated to guide material design. My vision is to build a research program focusing on developing fundamental science linking polymer structure & dynamics and function in novel materials with switchable/tunable properties, and engineering applications from ion-mediated supramolecular assemblies (Figure). Key areas of the experimental study will cover:

1. Molecular View on Ionic Supramolecular Copolymer Structure and Dynamics

2. Design and Fabricate Nanostructured Polymer Blends with Well-Defined and Tunable/Switchable Properties

3. Manufacturing Ion-Mediated Polymer Assemblies that Aid in Dynamic Compatibilizations

Research Experience

My Ph.D. research with Prof. Timothy Lodge at the University of Minnesota concerned the thermodynamics and phase behavior of polymer blends in the presence of added salt. I mapped out the phase diagrams of two salt-containing binary homopolymer blends, where a minimal amount of salt led to substantial immiscibility and the phase boundary curve became massively asymmetric. In addition to the experiments, a recent detailed theory by Prof. Zhen-Gang Wang at Caltech was applied, which fit the data reasonably well. Moreover, leveraging advanced scattering techniques (X-ray and neutron), I systematically studied the nanostructures in salt-doped A/B/AB ternary blends, where a highly conductive bicontinuous microemulsion with controllable domain size and a surprising C15 Laves phase with a giant unit cell (>120 nm) were discovered, and the formation mechanism was elucidated.

To deepen my understanding of polymer physics and polymeric materials design, and broaden my research background, I pursued a collaborative post-doctoral program with Prof. Rachel Segalman at UC Santa Barbara, where I focused more on the rational design of ion-containing materials with high performance in specific applications, e.g., developing novel polymer electrolytes with high ionic conductivity & lithium-ion selectivity, and compatibilized homopolymer blends with interchain electrostatic interactions, which can be exploited in plastic waste upcycling. My expertise in polymer synthesis and characterization of both structural and dynamic properties will enable me to make good progress on the proposed interdisciplinary research program with the theme of “Dynamic Nanoscale Assembly of Ion-Containing Polymers.”

Teaching Interests

The two research groups I participated in are highly interdisciplinary and based in the Chemistry, Chemical Engineering, and Materials Science Departments. The professional training I received and my research experience prepared me well to teach the following core courses in Chemistry, Chemical Engineering, and Polymer Science: Physical Chemistry, Thermodynamics, Transport Processes, as well as Polymer Physics and Chemistry. In addition, I would be excited about potentially sharing my expertise in advanced polymer characterization by developing special topics courses or labs, such as X-ray and neutron scattering, thermal analysis, and rheology.

My goal in education is NOT inputting knowledge but guiding students to understand the subject step by step. I will start with a simplified model system that can be analyzed thoroughly; then, the students can apply their understanding to solve new problems independently or collaboratively. I will encourage them to design experiments to validate their findings if applicable. In the laboratory, I will actively seek to foster an inclusive and collaborative research environment where students and postdocs can have frequent discussions and develop critical thinking and interdisciplinary skills.

Selected Publications

1. Xie, S.; Lodge, T. P. Phase behavior of binary polymer blends doped with salt. Macromolecules 2018, 51, 266-274.

2. Xie, S.; Meyer, D. J.; Wang, E.; Bates, F. S.; Lodge, T. P. Structure and properties of bicontinuous microemulsions from salt-doped ternary polymer blends. Macromolecules 2019, 52, 9693-9702.

3. Xie, S.; Zhang, B.; Mao, Y.; He, L.; Hong, K; Bates, F. S.; Lodge, T. P. Influence of added salt on chain conformations in poly(ethylene oxide) melts: SANS analysis with complications. Macromolecules 2020, 53, 16, 7141–7149.

4. Xie, S.; Lindsay, A. P.; Bates, F. S.; Lodge, T. P. Formation of a C15 Laves phase in salt-doped A/B/AB ternary polymer blends. ACS Nano 2020, 14, 10, 13754-13764.

5. Xie, S.; Zhang, B.; Bates, F. S.; Lodge, T. P. Phase behavior of salt-doped A/B/AB ternary polymer blends: the role of homopolymer distribution. Macromolecules 2021, 54, 14, 6990–7002.

6. Xie, S.; Nikolaev, A.; Nordness, O. A.; Llanes, L. C.; Jones, S. D.; Richardson, P. M.; Wang, H.; Clément, R. J.; Read de Alaniz, J.; Segalman, R. A. Polymer electrolyte based on cyano-functionalized polysiloxane with enhanced salt dissolution and high ionic conductivity. Macromolecules ASAP doi.org/10.1021/acs.macromol.2c00329