Collaborative Research: Measurement, Simulation, and Theory of Molecular Connectivity Effects on Nanoscale Interfacial Rheology of Glass-Forming Fluids

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If you zoomed into many of the modern materials that empower energy storage, enable water purification, or even make up the tires on your car, you would find that their essential structures are only hundreds of atoms across, and at the same time are chemically connected in vast spaghetti-like strands. These “polymeric nanomaterials” open the door to new technologies that can transform our life, economy, and national defense. A major reason for their promise is also their greatest challenge: mysteriously, the interfaces that pervade these polymeric nanomaterials cause them to behave dramatically differently than traditional materials. This award aims to solve a key piece of this mystery: why do these materials deform very differently in the vicinity of these microscopic interfaces? How can we design them to control this deformation behavior and thus fabricate them more economically, further improve their properties, and ultimately enable new technological advances? These questions will be answered via experiments that zoom in to the nanometer scale to observe how these materials flow and deform. At the same time, supercomputer simulations will visualize how molecules’ movements underlie this deformation. Ultimately, these results will drive the development of a theory that explains these materials’ behavior and empowers material engineers to improve their design and drive new technological advances. The effort will be integrated with a joint Princeton and University of South Florida outreach program exposing diverse high school students to experimental and computational research on interfaces.This award will establish a predictive theoretical understanding of nanoscale gradients in rheological response at interfaces in glass-forming fluids. These gradients emanate at least in part from the presence of a glass transition temperature gradient at interfaces. However, when this gradient is spanned by large molecules, particularly in the presence of surface adsorption, it is not clear how it controls alterations in rheological response. Work aims to (1) establish a theory of alterations in linear rheology in the nanoscale vicinity of free surfaces, (2) extend this theory to treat buried interfaces relevant to composites and multi-phase fluids, and (3) establish a new strategy for altering near-interface rheological response. To support new theory development, an experimental metrology to measure time-resolved nanocreep will be combined with simulations probing gradients in rheology and chain dynamics. Predictive understanding established by this work will transform the understanding, prediction, and design of flow of interfacially-rich fluids, such as nanoparticle-laden fluids, thin films, and nanostructured multiphase fluids.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.