Research

Mission Statement

We study the fascinating molecular assembly processes, such as nucleation, crystal growth, aggregation, etc, which critically impact the solid-state properties of materials (e.g. thermodynamic, kinetic, electronic, optical, mechanical). We are particularly interested in the highly non-equilibrium molecular assembly processes during additive manufacturing of soft functional materials. It is our goal to control the solid-state properties by understanding the fundamental molecular assembly processes, and ultimately, to achieve additive manufacturing for a future of cleaner environment and greener energy.

Research Themes

The hierarchical assembly of conjugated polymers has gained much attention due to its critical role in determining the optical/electrical/mechanical properties. The hierarchical morphology encompasses molecular scale intramolecular conformation (torsion angle, chain folds) and intermolecular ordering (π-π stacking), mesoscale domain size, orientation and connectivity, and macroscale alignment and (para)crystallinity. Such complex morphology in the solid state is fully determined by the polymer assembly pathway in the solution state, which in turn is sensitively modulated by molecular structure and processing conditions. However, molecular pictures of polymer assembly pathways remain elusive to date. We leverage a wide range of in situ and ex situ structural characterization techniques to elucidate the journey of conjugated polymer assembly from solution to the solid state, under near and far-from-equilibrium conditions.

Recent years, we have focused on understanding chiral liquid crystal mediated assembly of achiral conjugated polymers, a phenomenon we discovered by serendipity. Intimately connected to the rule of life, chirality remains a long-time fascination in biology, chemistry, physics and materials science. When applied to functional polymers, chirality may give rise to intriguing optical, electronic, and biological properties unimagined before. In addition, we are also interested in understanding pre-aggregation mediated assembly pathway of organic solar cells, which sensitively modulate the power conversion efficiency. We are working to unravel how molecular structures define pre-aggregates formation, their hierarchical structures and the ultimate device performance. This work has been highlighted on Illinois News Bureau.

Key papers

[1] Park, K. S.*; Kwok, J.J.*; Diao, Y. et al, “Tuning Conformation, Assembly and Charge Transport Properties of Conjugated Polymers by Printing Flow”, Science Advances, 2019, 5, 8, eaaw7757. DOI: 10.1126/sciadv.aaw7757

[2] Xu, Z.; Park, K.S.; Diao, Y. “What is the Assembly Pathway of a Conjugated Polymer from Solution to Thin Films?”, Frontiers in Chemistry, 2020, 8:583521. DOI: 10.3389/fchem.2020.583521 (Invited for the “Women in Science: Chemistry” article collection)

[3] Park, K.S.*; Kwok J.J.*; Kafle, P.*; Diao, Y. “When Assembly Meets Processing: Tuning Multiscale Morphology of Printed Conjugated Polymers for Controlled Charge Transport”, Chemistry of Materials, 2021, 33, 469–498, https://doi.org/10.1021/acs.chemmater.0c04152 (Invited perspective for the “Up and Coming” series)

We are deciphering the molecular origin of cooperativity in structural transitions, a phenomenon long used by living systems for circumventing energetic and entropic barriers to yield highly efficient molecular processes. Ultrafast, reversible cooperative transitions give rise to the shape memory effect, which is widely applied to designing medical devices, drug delivery vehicles, actuators and sensors in the automotive and aerospace industry. Surprisingly, cooperative transitions are rarely studied in molecular crystals, and thus its molecular mechanism remains unclear. Combining in situ polarized microscopy, single crystal X-ray diffraction, Raman spectroscopy and solid-state NMR, we are working to discover the molecular design rules of cooperative transitions in electronic crystals triggered by thermal, mechanical energy and light. We are also applying cooperative transitions to realize shape memory electronics and superelastic, strain-resilient single crystal electronic devices. This work has been highlighted on Illinois News Bureau and Beckman Institute.

Key papers

[1] Chung, H.; Dudenko, D.; Zhang, F.; D’Avino, G.; Ruzie, C.; Richard, A.; Schweicher, G.; Beljonne, D.; Geerts, Y.H.; Diao, Y. “Rotator Side Chains Trigger Cooperative Transition for Shape and Function Memory Effect in Organic Semiconductors”, Nature Communications, 2018, 9, 278. DOI:10.1038/s41467-017-02607-9

[2] Chung, H.; Chen, S. (undergraduate); Sengar, N.; Davies, D.W.; Garbay, G.; Geerts, Y.H.; Clancy, P.; Diao, Y. “Single Atom Substitution Alters Polymorphic Transition Mechanism in Organic Electronic Crystals”, Chemistry of Materials, 2019, 31, 21, 9115-9126. DOI: 10.1021/acs.chemmater.9b03436

[3] Park, S.K.*; Sun, H.*; Chung, H.; Patel, B.B.; Zhang, F.; Davies, D.W.; Woods, T.J.L; Zhao, K.*; Diao, Y.* “Super- and Ferro-elastic Organic Semiconductors for Ultraflexible Single Crystal Electronics”, Angewandte Chemie International Edition, 2020, 59, 2-11. https://doi.org/10.1002/anie.202004083

[4] Park, S.K.; Diao, Y. “Martensitic Transition in Molecular Crystals for Dynamic Functional Materials”, Chemical Society Reviews, 2020, 49, 8287-8314.  https://doi.org/10.1039/D0CS00638F (Invited for the “2020 Emerging Investigator Issue”)

3D printing (additive manufacturing) technologies have achieved widespread commercialization for melt extrusion of thermoplastic structural polymers (a.k.a. fused deposition modeling), thanks to their low cost, reliability, and ease of use. Expanding the material palette to functional materials is a revolutionary next step that has been recently reported for cell-laden gels, electronic materials, and even pharmaceutical drugs, although the overwhelming focus has been on determining suitable ink formulations for material delivery, with less attention paid toward the molecular assembly process during deposition. Integrating molecular assembly with 3D printing offers a compelling avenue to attaining structural control down to the nanoscopic and molecular scale. Such precision of structural control has been challenging with current 3D printing approaches. In collaboration with Guironnet, Sing and Rogers groups, we leverage nanoscale assembly of bottle-brush block co-polymers for 3D printing of structure color. By custom design of an integrated hardware/software platform, we aim to dynamically modulate printed structures at the nanoscale to program the structure color as we print without changing the ink material. We tap into our expertise of polymer assembly to precisely control the kinetics of microphase separation during printing, which is key to dynamic modulation of structure color. This work has been highlighted on Illinois News Bureau.

Key papers

[1] Patel, B.B.; Walsh, D.J.; Kim, D.H. (undergraduate); Kwok J.J.; Lee, B.; Guironnet, D.; Diao, Y. “Tunable Structural Color of Bottlebrush Block Copolymers through Direct-Write 3D Printing from Solution”, Science Advances, 2020, 6, eaaz7202. DOI: 10.1126/sciadv.aaz7202

In order to meet the food requirement of nutrient and safety for astronauts in long space missions, it is important for researchers to develop a way of cultivating fresh green vegetables in space. Great progress has been made to achieve plant growth in space in previous works by NASA, including plant growing payload such as Advanced Plant Habitat (APH) and the Vegetable Production System (Veggie). These units require substantial human effort to maintain and optimize and do not afford detection of plant growth and health condition remotely and autonomously. Moreover, simple inspection is insufficient for identifying the specific stress a plant is enduring, especially at the early stage. To address these challenges, we are developing light-weight, flexible and stretchable organic-electronics based chemical and strain sensors for autonomous, remote monitoring of plant health and plant growth. The potential impact of our approach goes beyond cultivating vegetables for plants. Our technology could contribute to understanding how plants cope with climate change, and to enhancing crop productivity for feeding the growing human population. Read more about this project in LAS News.

Related Papers

[1] Zhang, F.; Qu, G.; Mohammadi, E.; Mei, J.; Diao, Y. “Solution-Processed Nanoporous Organic Semiconductor Thin Films: Toward Health and Environmental Monitoring of Volatile Markers”. Advanced Functional Materials. 2017, 27, 1701117. DOI: 10.1002/adfm.201701117 (back cover)

[2] Zhang, F.*; Lemaur, V.*; Choi, W.; Kafle, P.; Seki, S.; Cornil, J.; Beljonne, D.; Diao, Y., “Repurposing DNA Binding Agents as H-bonded Organic Semiconductors”, Nature Communications, 2019, 10, 4217. https://doi.org/10.1038/s41467-019-12248-9

[3] Kafle, P.; Zhang, F.; Schorr, N.B.; Huang, K.-Y.; Rodríguez-López J.; Diao, Y. “Printing 2D conjugated polymer monolayers and their distinct electronic properties”, Advanced Functional Materials, 2020, 30, 1909787. DOI: 10.1002/adfm.201909787

Organic photovoltaics (OPV) are next-generation devices for harvesting renewable energy that are becomingly increasingly desired over traditional silicon solar cells. The two primary challenges preventing the widespread adoption of OPV relative to silicon-based solar cells are inferior power conversion efficiency and apparent instability to sunlight. Working with synthetic chemists and computer scientists, we aim to develop new machine learning tools to guide the discovery of highly efficient and indefinitely stable organic photovoltaics via automated synthesis, manufacture, and testing at the device level. Check out the Molecule Maker Lab Institute for more.

Diao Research Group

164 Davenport Hall

607 S. Mathews Ave., 

Urbana, IL 61801

prof. Ying Diao

213 ROGER ADAMS LABORATORY

600 S. MATHEWS AVE.,

URBANA, IL 61801

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