Soft matter physics of polymer-based materials and proteins

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The ability to control the microscopic interactions between synthetic polymers or naturally-occurring proteins and small particles or structures could ultimately lead to the development of new materials with properties tuned for particular applications, or to improved treatment or prevention of diseases. The goal of my research program is to understand these small-scale polymer interactions in certain polymer-based fluids and biological systems. In man-made materials, interactions between polymers and added nanoparticles affect the way the polymers can move, which in turn modifies bulk properties such as flow behavior, elasticity, and electrical conductivity. We will perform mechanical, electrical, and optical experiments on well-characterized polymer-nanoparticle composite materials and polymer gels to learn how nanoparticles and surfaces affect the dynamics of the polymer chains and material properties. Some materials (e.g., hair gel) are solid-like under some conditions, but flow when the small-scale polymer interactions are overcome by an applied force. We will use mechanical and optical measurements to investigate the large- and small-scale features of the process by which these materials start to flow. Better fundamental understanding of this process could lead to improved optimization of industrial flows. In living systems, interactions between proteins and microscopic biomineral crystals control the growth of bone, teeth, and kidney stones. We will investigate how this works by using laser light scattering to measure the size of precipitating mineral crystals in the presence of proteins or peptides. It is believed that interactions between proteins and small-scale structure in the membrane of immune-system cells known as macrophages affect their ability to destroy pathogens. We will learn how macrophages exert forces on pathogens by studying the motion of proteins in the cell membrane and measuring the forces generated by macrophages as we manipulate the membrane structure. Results from these experiments will improve our understanding of the biophysics involved in these biologically important processes. Finally, we will develop new instruments and techniques for measuring the viscoelastic behavior of fluids containing polymers and nanoparticles. While my approach to all of these problems is physics-based, much of the proposed research is interdisciplinary and collaborative. The undergraduates, graduate students, and postdoctoral researchers who will contribute to this research will use state-of-the-art instruments and techniques. Overall, this innovative research will provide us with a better fundamental understanding of nanoscale polymer interactions and will have impact in fields as diverse as materials science, fluid dynamics, and microbiology. **