The REN group works on the forefront of material chemistry, including materials-by-design, synthesis, self-assembly, and transformative manufacturing of multifunctional materials with an emphasis on novel magnetic, electronic, thermal and mechanical properties for emerging technologies. We are committed to realizing our vision by focusing on the following main research thrusts: (1) Strongly correlated molecular matters for unusual ferroics and energetics; (2) Extreme environment materials with thermal management – Printable ultrahigh temperature ceramics and metals, and thermally conductive polymers; and (3) Carbon-sequestration insulation materials for sustainability and energy applications.
1. Materials design and assembly of strongly correlated matters for unusual magnetic, electronic, ferroic and energetic properties
The hierarchical self-assembly of complex nanostructures from simpler building blocks is often driven by non-bonded vdW forces – quantum mechanical phenomena that are ubiquitous in nature and arise from electrodynamic correlations between instantaneous charge fluctuations in matter. These non-covalent interactions have an influence that extends well beyond binding and lattice energies, and encompasses the structural, mechanical, spectroscopic, and even electronic signatures of condensed matter. As such, even slight variations in the magnitude of these interactions can impact the observed properties and functionality of a given organic material. This combined theoretical and experimental project seeks to establish a new class of organic functional materials by tuning the complex interplay between dimensionality, topology, intermolecular interactions, and vdW forces occurring in the complex self-assembly process. The emphasis is framing the design principles underlying the growth of vdW-bound 2D and 3D molecular electronic crystals that consist of chemically and electronically distinct donor and acceptor molecules with specific and directional intermolecular interactions, where Structure | Composition | Property relationships will be uncovered in this project.
The other emphasis of this project is tunable control over the emergent properties for this new class of strongly correlated molecular crystals across the optical, electronic, magnetic, and mechanical energy domains (high temperature conductors, superconductors, magnets, and multiferroics). In this regard, these vdW-bound molecular crystals combine two or more physical properties in the same lattice. Furthermore, by exercising control over the size, shape, and charge states of the molecular building blocks, one can confine this novel functionality within a given dimension or across the entire 2D or 3D crystals. This class of molecular materials can also absorb and exchange energy through different physical mechanisms, tunable charge-transfer and tenable vdW interactions controlled by phase transition and chemical combinations, which is far different from short-range or amorphous phases. The emergent physical properties (e.g., room temperature ferroelectricity, magnetism, superconducting, multiferroics, and light-matter coupling properties) of these molecular crystalline materials are investigated using unique real-time capabilities at a high spatial & temporal resolution.
2. Lightweight bioinspired materials with thermal management – Superinsulation ultrahigh temperature ceramic aerogels, and Thermally conductive polymers
Ceramic aerogels have attracted the extensive interests due to its ultralow thermal conductivity for the use in extreme temperature environments. Such high thermal insulation is derived from its mesoporous microstructures, high porosity, and low density. Highly porous aerogel material is generally formed through a sol-gel process, including hydrolysis/gelation, aging, and drying. The objective of this project is to explore bioinspired manufacturing of mechanically robust and ultrahigh temperature superinsulation ceramic aerogel materials (both transparent and opaque aerogels) under physiological conditions.
Ultra-high molecular weight polyethylene (UHMWPE) is a linear homo-polymer bearing -(CH2-CH2-)n – as the repeat unit and having an average molecular weight more than 3.1 million g/mol (n ≈ 110,000 monomeric units). Its superior mechanical properties derive from the enormous number of covalently linked monomeric units giving rise to UHMWPE. Despite weak van der Waals interactions between polymer chains, the presence of a large amount of aligned overlaps between neighboring chains can lead collectively to high intermolecular strength. Due to its excellent mechanical properties, chemical stability and effective impact load damping, UHMWPE derived materials have been extensively used in military armor, and orthopedic bearing materials, etc. The mechanical and thermal properties of UHMWPE materials are inextricably linked to their crystalline organization. Bulk UHMWPE is primarily comprised of crystalline domains, which are bridged by nanoscale amorphous. Towards the above objectives, we explored the UHMWPE based matrix for its high thermal conductivity, excellent mechanical properties, low coefficient of thermal expansion, nontoxicity, and high electrical resistivity over a wide range of operating temperatures.
3. Preceramic and metallic precursor materials and manufacturing of flexible hybrid electronics for use in extreme environments
The ever-increasing need for high-throughput electronic device miniaturization demands the printing of flexible hybrid electronics without sacrificing performance, lightweight and conformability. In this context, the development of advanced materials is required to operate under extreme environments (high temperature beyond 1,500 oC, thermomechanical and thermocorrosive conditions). Such high-temperature operation poses significant material challenges. The aforementioned challenges compel us to seek out new high temperature conductors and ultrahigh temperature ceramics capable of carrying a large amount of electric current and also dissipate the excessive heat in an efficient manner so as to maintain the reliability of printed electronic devices and thermal protection systems.
4. Additive manufacturing of carbon-sequestration biogenic materials for sustainable building insulation applications
“Built-by-Nature” is a new initiative to accelerate the transition of sustainable buildings as a global carbon sink. Emerging bio-based materials, i.e. straw and hemp, with high carbon content (~90% instead of ~50% for wood) will become a major source to be explored. However, challenges associated with this wave of bio-based construction have been identified as the main materials science barrier to address, such as its poor thermal insulation and weak structural performance, fire and moisture/condensation risk. Nature-inspired functional gradient materials immensely evolved in the seashells, fish scales, bone, teeth and plants (e.g., bamboo), which exhibit a systematic change in microstructure and composition to locally tailor structural insulation properties as a result from multi-axial stress states and material composition gradience. Might it be possible to transform biogenic materials into powerful carbon-sink buildings to mitigate climate change?
5. Redox Manufacturing of rare-earth-free high energy product magnets
The energy product of spring magnets is partially dictated by the magnetocrystalline anisotropy of hard magnetic component (the current supermagnets are primarily based on Rare-Earth based alloys). Replacing non-sustainable and strategically undesirable rare-earth elements is one of the most critical challenges. This project investigates sustainable rare-earth-free alloy nanomagnets (hard magnets) by using metal-redox reduction approach to stabilize and control nanostructures for high energy product nanomagnets.
