UNDERSTANDING AND CONTROLLING COMPLEX CHEMICAL PROCESSES

Understanding and controlling complex chemical processes requires the ability to perform multimodal imaging across all length and time scales. That is, researchers would like the capability to image a material or a process using multiple techniques, including those that can “focus” on a particular aspect of the material or process (through varying length scales), as well as capture images at appropriate time dimensions to acquire necessary information.

An overarching objective for future breakthroughs using chemical imaging techniques is to gain a fundamental understanding and control of these complex chemical structures and processes. While this is the grand challenge for chemical imaging, more specific requirements need to be addressed in order to meet this comprehensive challenge. These include: understanding and controlling self-assembly, complex biological processes, and complex materials. Each of the challenges is amplified further below.

Understanding and Controlling Self-Assembly

The self-assembly of small molecular units into larger structures is a common and important occurrence in nature. In the biological realm, proteins and RNA fold into specific functional conformations. Cells divide and communicate with each other by rearranging subcellular units. Some theorists hypothesize that the spontaneous formation of lipid vesicles is responsible for the beginning of life. Outside biology, we marvel at the growth of snowflakes. We find numerous uses for soap and liquid-crystal displays. We make materials with varying properties by tuning the degree and the nature of aggregation. Indeed, many proposed methods for creating nanomaterials are based on self-assembly.

Molecular assemblies are formed through strong and weak chemical forces. Understanding the types, magnitudes, directions, and distances associated with these interactions is thus of fundamental and practical importance. Chemical imaging can elucidate many of these processes by providing spatial and temporal relationships among the interacting units. We would like, at one extreme, to follow the rotation, formation, and breakage of individual bonds and, at the other, to investigate cooperative effects and sequences of events over extended domains. The same or different small assemblies can be tracked as they grow into larger assemblies. In addition, chemical transformations within these structures can be monitored to elucidate environmental effects on reactivity and ultimately can be controlled by the patterned exposure to electromagnetic radiation and other fields.

To gain better understanding of and to control molecular assembly processes, one needs chemical imaging techniques that can follow interactions at a broad range of length and time scales. During assembly, it would be advantageous to record inter- and intramolecular orientations and distances at picosecond to second



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