Single Molecule Studies for Characterizing Dynamical and Mechanical Properties of Glassy Systems

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Professor Laura Kaufman of Columbia University is using single-molecule microscopy methods to study structural domains in glassy polymers. Glasses appear to be solid, but in contrast to crystals, they have amorphous structures that are more akin to liquids. Polymers, like plastics and rubbers, frequently form glassy solids. While they are ubiquitous in modern life, they still exhibit poorly understood behaviors. For example, they appear to be made up of small structural domains that slowly move through the seemingly solid material, oftentimes at different speeds. Professor Kaufmann and her students are watching the fluorescence from individual molecules embedded within polymers to track the movement of these domains. Their discoveries could inform the design of materials for use in a wide range of applications, from household goods to solar cells and biomedical materials. The students engaged in this research learn a broad range of experimental techniques and analysis approaches that are applicable to many areas of science and technology. The Kaufman group also regularly engages with K-12 students through talks and demonstrations that introduce students to the unusually interesting properties of glassy materials. Professor Kaufman will refine and extend single molecule imaging. The addition of complementary approaches is expected to provide for a more detailed view of dynamic heterogeneity in polymeric glass formers. Fluorescence signals detected from novel probes will be followed over time scales ranging from minutes to hours and used to characterize the length scale, organization, and mechanical properties of heterogeneous regions in glassy polystyrene. First, a set of experiments comparing the behavior of free and tethered single molecule probes in physically entangled and chemically cross-linked polymers will elucidate aspects of the spatial extent of heterogeneous domains. Following this, investigations into bulk and local mechanical properties in polystyrene below its glass transition temperature, including following perturbations, will be undertaken in this and similar systems. Using a modular approach, the Kaufman group will perform integrated imaging and rheology experiments to detail connections between bulk mechanical properties, local free volume, and spatiotemporally local dynamics in glasses.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.