Rheo-Particle Tracking Velocimetry: Measurement, Analysis and Application
Flow characterization is critical to understanding the processing and application of a wide range of rheologically complex materials including polymer solutions, colloidal suspensions, surfactants, soft gels, emulsions and foams. This is particularly true for rheological measurements, which are typically predicated on the assumption of viscometric flow – i.e., the flow geometry produces a relatively homogeneous shear rate and shear stress within the material. However, a number of rheological phenomena are known to produce inhomogeneities in otherwise viscometric flows. These include wall slip, yielding and shear banding, just to name a few. Although the presence of these phenomena is often inferred from the rheological measurement itself, these measurements are compromised by the presence of non-uniform flow, significantly complicating data interpretation and obscuring the underlying rheological properties of the material.
Rheo-particle tracking velocimetry (rheo-PTV) is a powerful, high-resolution technique to characterize the rheology and flow behavior of complex materials. By simultaneously measuring the fluid velocity and stress, rheo-PTV provides rich information regarding the coupling of nonlinear rheology and flow behavior, and has been used to elucidate the mechanisms and behavior of various flow instabilities that are common to large classes of materials. In recent years, rheo-PTV accessories for conventional rotational rheometers have been commercialized, making this powerful yet previously uncommon capability available to a wide potential community of users.
This webinar is intended to provide an introduction to the rheo-PTV technique, including principles of measurement and common instrumentation, practical aspects of experimental design, and data analysis and interpretation. In particular, we will highlight a number of recent developments in quantitative analysis of PTV data that provide precise, local measures of fluid flow, rheology and structure that would be impossible to infer from rheological measurements alone. These analyses are exemplified by several example applications of the rheo-PTV technique, which underscore the deep insight that can be obtained into the rheology of complex fluids and soft materials by understanding the coupling between rheology and flow.
Matt Helgeson is an Associate Professor in the Department of Chemical Engineering at UC Santa Barbara, where he is also a faculty member and IRG co-leader of the Materials Research Laboratory (an NSF MRSEC). He received his B.S. in Chemical Engineering at Carnegie Mellon University in 2004, and his Ph.D. in Chemical Engineering at the University of Delaware in 2009. He performed postdoctoral research at MIT before joining the faculty at UCSB. Prof. Helgeson’s research focuses on designing and processing complex fluids with well-specified rheological properties, especially those involving colloids in structured liquids. Prof. Helgeson’s research has been recognized with a number of awards, including Early Career Awards from both the National Science Foundation (2013) and Department of Energy (2015), a Hellman Foundation Faculty Fellowship (2016), and both the Victor K. LaMer Award (2011) and Unilever Award (2016) from the American Chemical Society.
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