MAE Seminar Series - Jessica Shang, University of Rochester

Abstract: Matter at high energy density (HED) conditions is abundant in our universe, from planetary interiors such as our Earth, to stars. Pressures exceed 100 GPa (a million atmospheres), and ordinarily incompressible materials become quite compressible. Modeling these geophysical flows, as well as those found in inertial fusion, requires knowledge of transport properties such as viscosity. However, predictions of viscosity of different species from first principles vary widely, particularly in the warm dense matter regime, and experimental benchmarking is needed. We can access these high pressures by dynamically compressing materials at large-scale laser facilities especially designed for HED experiments. In this talk, we will describe various methods to probe viscosity over nanosecond time scales, using implicit measurements at user facilities at the University of Rochester Laboratory for Laser Energetics. In one experiment, we measured the viscosity of a hydrocarbon polymer via the displacement of dense microspheres embedded in the material, imaged with x-ray radiography. The trajectories of the particles was corroborated with an unsteady particle forcing model to estimate the polymer's dynamic viscosity from the viscous contributions. In the second experiment, we tracked the evolution of a rippled shock front in fused silica, where viscosity is expected to modify the timescale of the ripple’s decay. Our work illustrates the experimental challenge in producing and quantifying small viscous perturbations, and more broadly, linking our estimates for viscosity in non-equilibrium conditions to their theoretical counterparts. 

Bio: Jessica Shang is an Associate Professor of Mechanical Engineering at the University of Rochester and holds a secondary appointment at the Laboratory for Laser Energetics. She earned a BA from Harvard University, an MPhil from the University of Cambridge, and a PhD in Mechanical and Aerospace Engineering from Princeton University. Prior to joining UR, she did her postdoctoral work in Pediatrics at the Stanford School of Medicine, and received an NIH T32 postdoctoral fellowship with the Stanford Cardiovascular Institute. She is the recipient of an ONR Summer Research Faculty Fellowship (2017) and the NSF CAREER Award (2021). Her research group is interested in interdisciplinary problems in in fluid mechanics, ranging from seal whiskers to high energy-density flows. 

Host: Dr. Chen Cui