“It’s just like cooking,” insists Ziyi Zhang, an avid home chef and Welch Postdoctoral Fellow at The University of Texas at Austin, as he explains that synthesizing nanoparticles is the “easy” part of his project.
Zhang is designing organic ligands that link nanoparticles together with reversible bonds into “superstructures.” By controlling, or tuning, the linking chemistry of these structures, Zhang is engineering these bonds to be reversible in response to external stimuli, such as temperature, electric fields, or chemical environment, resulting in different functions and properties.
Tunable nanocrystal structures could enable advances in energy storage, optical materials, and adaptive electronics. For example, temperature-sensitive structures could function as “smart fuses” in batteries, temporarily disconnecting at high temperatures to reduce overheating risks and reconnecting when conditions normalize. Similarly, other nanoparticle assemblies could lead to optical coatings or devices whose light absorption changes on demand, like smart windows that dynamically regulate heat and light transmission.
“We are engineering bonds that reversibly form and break under controlled conditions. The final goal of this project is to show the tunability of this versatile system. But now we are in the very early steps of trying to explore those parts one by one,” Zhang says.
The project involves two main steps. First, Zhang synthesizes inorganic nanoparticles that serve as the structural backbone. Then, the particles are functionalized with organic ligands “terpyridines” that allow them to connect through reversible metal coordination chemistry, forming higher-order three-dimensional networks. His work is co-advised by Eric Anslyn, Welch Regents Chair in Chemistry and Distinguished Teaching Professor at UT Austin, and Delia Milliron, Anthony C. Lembke Department Chair of Chemical Engineering and James and Judith Street Professor of Chemical Engineering of the University of Michigan.
A key scientific challenge lies in controlling the reversibility of the assembled structure. Because the linking kinetics depend on bond energies, the assembly responds sensitively to applied external stimuli, such as temperature gradients across the material. Zhang is exploring strategies to address this, including using multiple metal ions with different bonding strengths to create stepwise structural changes instead of simultaneous transitions.
“I am very grateful to The Welch Foundation for its support. The three-year term of the grant allows me to pursue longer-term scientific questions, develop an independent research direction, and plan ahead for expensive budget items. Also, I really enjoy the Welch Conference. It’s a great opportunity for us young researchers to get together and express our crazy ideas,” Zhang says.
Beyond the research itself, Zhang values mentoring undergraduate students and introducing them to hands-on laboratory work. Early exposure to real research, he believes, helps students understand how scientific discovery actually happens. That’s how it happened for him:
“When I was an undergrad, I joined a lab and did my first synthesis on my second day. The second day, because the first day was training. That impressed me a lot because I was really making the nanoparticle just as easy as cooking. For me, I think chemistry is the same as cooking. I love cooking.”
Looking ahead, Zhang hopes to continue a career focused on fundamental research and studying how chemical design at the smallest scales can lead to new classes of functional materials. For him, the uncertainty of fundamental science is part of its appeal: unlike engineering problems with predefined goals, exploratory research requires discovering the path forward step by step. That challenge, he says, is what makes the work exciting.
“In fundamental science, you only have a beginning point. You never know the final goal you can achieve. It’s just in your mind, where you can imagine a goal. That's my driving force to keep me in this fundamental research field. You are trying to find your own path. That’s very interesting.”