Bradley F. Chmelka Research Summary (September 2023)

Atomic-level materials and chemical engineering

Our research group seeks to understand and control the atomic-level processes that govern syntheses, processing, and resulting macroscopic properties of heterogeneous engineering materials. Our objectives are to acquire, understand, and use such insights to establish new atomic-scale design criteria for materials with novel properties for engineering applications. Our recent interests fall into 3 main areas:

Our individual projects are selected for their fundamental interest and technological importances, most of which are motivated by energy- or environmentally-related applications. The above themes and materials share common features at a molecular level, notably the importance of interfaces and interactions between dissimilar components that exert crucial influences over how the materials are formed and their resulting properties. Often crystallization or self-assembly processes are important, along with the thermodynamic and kinetic considerations that govern associated phase behaviors, species distributions among different heterogeneous regions, and how these can be respectively controlled. Our investigations are governed by general hypotheses that the atomic-level compositions, structures, dynamics, and surface interactions of heterogeneous materials can be measured, understood, and correlated with their macroscopic catalytic, opto-electronic, electrochemical, and/or mechanical properties. We exploit such information in the subsequent design or optimization of materials with properties that lead to improved or new chemical engineering applications.

Efforts to acquire atomic-level insights on heterogeneous multicomponent materials are often challenged by the absence of long-range atomic order, by low sensitivity, and/or by the low resolution of conventional characterization methods. In many cases, such challenges can be overcome or mitigated by using state-of-the-art techniques of nuclear magnetic resonance (NMR) spectroscopy, which enable the detection and identification of atomic species and their interactions, even those that are disordered, dilute, or at surfaces. Crucially, we synthesize and process in-house nearly all of the samples and materials used in our investigations, which permits us to test our hypotheses and provides close feedback between our characterization results and the material properties that we seek to understand and control. Atomic-level NMR studies are combined and correlated with complementary X-ray scattering, electron microscopy, molecular modeling, macroscopic property measurements, etc., which are collectively vital to our overall materials synthesis and property objectives.

Many of my group’s materials-motivated interests have driven us to develop or adapt non-routine NMR methods to confront previously intractable problems in the characterization of heterogeneous solids. This includes the use of new NMR probehead designs, pulse sequences, sample handling procedures, and data analysis strategies to improve the detection sensitivity or resolution of signals from complicated engineering materials. Doing so has allowed us to identify and correlate the atomic-level compositions and structures of heterogeneous materials, especially at surfaces, with larger length scale structures and macroscopic properties. Our unusual combination of synthesis and characterization capabilities has been key to our progress and continues to open creative opportunities across the fields of chemical engineering, physical chemistry, and materials science.