Molecular self-assemblies are abundant in both nature and man-made materials and their applications range from drug delivery and biomaterials to water capture and catalysis. These materials of interests include biomimetic materials, metal-organic frameworks, and biological tissues. Regardless of the application though, understanding fundamental chemical, physical and geometric properties is important to fully understand a material’s potential function and design future materials. However, with self-assemblies frequently forming architectures on the order of 10s of microns, a sample would be composed of self-assembly domains that differ in the aforementioned properties. This spatial heterogeneity warrants new techniques to spatially resolve materials with chemical identities, in order to elucidate these fundamental properties.
Our group focuses on implementing nonlinear optical approaches such as vibrational sum-frequency generation (VSFG), a second-order phenomena, into imaging techniques. VSFG is highly dependent on the chemical, physical and geometric properties of the material. We have developed two collinear VSFG microscopy platforms. The first, a transient VSFG microscope disentangles the interaction between different chemical environments within a sample such as chirally templated water in the self-assembly SDS@2β-CD, comprised of sodium dodecyl sulfate and β-cyclodextrin. The second, a line-scanning design, builds on the success of the first variant and collects polarization resolved images rapidly, which enables geometric profiling of samples with small architectures or defects. Both platforms offer high resolution imaging, less than 2μm, which enables differentiation between spatial domains of many self-assembled materials. With the ability to resolve materials from their spatial, temporal and energy domains, we focus on understand structure and hydration of self-assembled materials and how they correlate to material mechanical properties and functions.