(3au) Multiscale Soft Materials Design for Energy and Environment

One of nature’s most powerful tools to combine disparate material properties in a synergistic way is to integrate dissimilar components at the nanometer scale. For example, mother-of-pearl, or nacre—the iridescent material lining the inside of seashells—is made almost entirely of brittle calcium carbonate. Nevertheless, it exhibits excellent toughness and mechanical resilience because the calcium carbonate plates are arranged in a “brick-and-mortar” fashion and glued together by a tiny fraction of biopolymers. Such a meticulous integration leading to a material with properties superior to the sum of the individual properties remains a challenge.

The overarching theme of my research is to utilize the state-of-the-art electron tomography in conjunction with electrochemical, spectroscopic methods for soft materials. My research will aim to understand materials synthesis–structure–functionality relationships to maximize desired properties and to solve technical problems in energy and environment systems.

Research Experiences:

My graduate work provided me with an in-depth tool kit for engineering hybridization at the macro- and molecular level that will be invaluable towards designing practical applications. In particular, I developed multifunctional hybrid materials to adapt mechanical flexibility and electrochemical performance synergistically, without sacrificing either properties. Flexible batteries with high energy storage and load-bearing mechanical properties are essential for emerging wearable devices and flexible electronics which provide portability, user comfort, and flexibility of device design. I developed flexible electrode materials for lithium ion batteries by preventing unfavorable phase separations between soft materials and inorganic materials. The flexible electrode mimics the brick-and-mortar structure of tough seashells, with V₂O₅ layers arranged in parallel and glued together by the copolymer. This structure significantly enhances mechanical flexibility and toughness without sacrificing the electrochemical performance of the batteries.

As another hybridization, I engineered surface-agonistic stretchable conductive coatings by mimicking the natural layer-by-layer structure of seashells. Stretchable, bendable, and foldable conductive coatings which provide stable functionality while undergoing mechanical deformation are also crucial for wearable electronics and biometric sensors. MXenes are currently booming as novel inorganic nanosystems in applications ranging energy storage and catalysis to biomedical applications due to their high electrical conductivity and the variety of elements they can be composed of. However, it is still extremely difficult to form thin MXene coatings that can withstand extreme mechanical deformation. I replicated the layer-by-layer structure of resilient seashells with negatively charged MXene and a cationic polyelectrolyte to synergistically integrate high conductivity, mechanical robustness, and mechanical flexibility into a composite coating material, and thereby address the main challenges in current MXene composites: loss of functionality under mechanical stress. I revealed the underlying mechanism of electromechanical coupling by using numerical modeling and geometric analysis.

To complete the foundation for my own research program, I cultivated an electron microscopy tomography–quantitative morphometry skill set during my postdoctoral work that I will couple with my engineering tool kit. Specifically, I developed low-dose electron microscope tomography that enables investigations of beam-sensitive soft materials with heterogenous nanoscale morphologies. As a model soft material, I studied thin polyamide membranes with the nonperiodic heterogenous nanostructures that emerge from synthesis. Polyamide membranes has been used in separation industries for over 30 years, however, the development of their predictive design remain a challenge. To address these issues, I bridged the structural organization in space and the functionality of materials using a 3D electron microscopy imaging-quantitative morphometry platform. I also demonstrated that reaction conditions can serve as a handle on structure parameters like pore structure, local curvature, thickness, and interconnectivity. To this end, I undertook low-dose electron tomography and quantitative morphometry efforts that provide a means to map out functionally relevant, 3D features of polyamide crumples and to extract a wide variety of transport-related properties.

My future research focuses concern (i) the ageing mechanisms of rechargeable batteries and the development of strategies to prolong their life up to 10 years, (ii) how loss of electromechanical properties of stretchable conductors could be mitigated by mimicking human elbow skin structure, where micro winkles exist and maintain flexibility over 80 years of human life. To address these questions, my research program will merge my expertise in soft materials, electrochemistry, hybridization engineering, and electron microscopy tomography-quantitative morphometry. In my future research, I will seek to develop fundamental understandings of the mechano-electrochemical and mechano-electrical response mechanisms and failure modes at both the macroscopic and atomic scale. My foundation in chemical engineering and materials science leaves me well-situated to undertake this research program in interdisciplinary engineering.

Teaching Interests:

In my academic career, I have had the great fortune of being a teaching assistant on multiple occasions, for courses covering chemical engineering thermodynamics (at Texas A&M University), separation processes (at Hanyang University). I also served as laboratory instructor in a course on numerical analysis for chemical engineers (at Texas A&M University). In the process, I was able to experience first-hand how an instructor’s passion could motivate and engage young, bright minds. I learned teaching know-how to provide additional support to students to tackle challenging subject matter and to improve lecture quality. In addition to my teaching assistant experience, I developed my teaching skills through ENGR681: Preparing Future Faculty-Professional Development at Texas A&M University.

Beyond the classroom, I have had the privilege of mentoring six undergraduates, two masters students and three PhD students in laboratories. More than half of them produced peer-reviewed publications and patents under my mentorship that are rewarding experience while pursing career in academia. I am interested and qualified in teaching most of the major courses for Chemical Engineering including Thermodynamics, Separation Processes, Transport Processes, Reaction Engineering, Physical/Organic Chemistry, Polymer Chemistry, Electrochemistry, Numerical Methods, and Advanced Mathematics for chemical engineers at both undergraduate and graduate level. Additionally, I am interested in developing special interdisciplinary topic courses at the graduate level on new research topics (e.g., Quantitative Data Analysis, Polymer-Inorganic Hybrid Materials).

Selected Publications (10 first author publications, 22 total):

[1] H. An, J. W. Smith, W. Chen, , Z. Ou, Q. Chen, “Charting the quantitative relationship between two-dimensional morphology parameters of polyamide membranes and synthesis conditions” Mol. Syst. Des. Eng. 2020, 5(1), 102-109.

[2] X. Li, H. An, J. Strzalka, J. L. Lutkenhaus, R. Verduzco, “Self-doped conjugated polymeric binders improve the capacity and mechanical properties of V₂O₅ cathodes” Polymers 2019, 11(4), 589.

[3] H. An, T. Habib, S. Sha, H. Gao, A. Patel, M. Radovic, M. J. Green, J. L. Lutkenhaus, “Water sorption in MXene-polyelectrolyte multilayers for ultrafast humidity sensing” ACS Appl. Nano Mater. 2019 2 (2), 948–955.

[4] H. An, X. Li, K. A. Smith, Y. Zhang, R. Verduzco, J. L. Lutkenhaus, “Regioregularity and molecular weight effects in redox active poly(3-hexylthiophene)-block-poly(ethylene oxide) electrode binders” ACS Appl. Energy Mater. 2018, 1(11), 5919.

[5] H. An, T. Habib, S. Sha, H. Gao, M. Radovic, M. J. Green, J. L. Lutkenhaus, “Surface-agonistic highly stretchable and bendable conductive MXene multilayers” Sci. Adv. 2018, 4(3), eaaq0118.

[6] M. Morris, H. An, J. L. Lutkenhaus, T. H. Epps III, “Harnessing the power of plastics: nanostructured polymer systems in lithium-ion batteries” ACS Energy Lett. 2017, 2(8), 1919-1936.

[7] C. Chalker*, H. An*, J. Zavala, A. Parija, S. Banerjee, J. L. Lutkenhaus, J. Batteas, “Fabrication and electrochemical performance of structured mesoscale open shell V₂O₅ networks” Langmuir 2017, 33(24), 5975-5981. (*co-first)

[8] H. An, X. Li, C. Chalker, M. Stracke, R. Verduzco, J. L. Lutkenhaus, “Conducting block copolymer binders for carbon-free hybrid vanadium pentoxide cathodes with enhanced performance” ACS Appl. Mater. Interfaces 2016, 8 (42), 28585.

[9] H. An, J. Mike, K. Smith, L. Swank, Y. Lin, S. Pesek, R. Verduzco, J. L. Lutkenhaus, “Highly flexible self-assembled V₂O₅ cathodes enabled by conducting diblock copolymers” Sci. Rep. 2015, 5, 14166.

[10] H. An*, D. Song*, J. Lee, E. Kang, J. Jaworski, J. Kim, Y. Kang, “Promotion of strongly anchored dyes on the surface of titania by tetraethyl orthosilicate treatment for enhanced solar cell performance” J. Mater. Chem. A 2014, 2, 2250. (*co-first)

[11] D. Song*, H. An*, J. Lee, J. Lee, H. Choi, I. Park, J. Kim, Y. Kang, “Densely packed siloxane barrier for blocking electron recombination in dye-sensitized solar cells” ACS Appl. Mater. Interfaces 2014, 6(15), 12422. (*co-first)