BSI Christmas Seminar and Lunch
Extensional Rheo-Optics of Complex Fluids in a Microfluidic Cross-Slot Device
Dr Simon Haward will present the above titled seminar in the final BSI seminar of 2011. The seminar will be followed by a Christmas sandwich buffet.
Abstract: A thorough characterization of the flow properties (rheology) of complex fluids containing long-chain molecules such as synthetic polymers, polysaccharides or proteins is vital for the optimization and understanding of a vast range of industrial, technological and biological processes. Many important flows, such as those encountered in ink-jet printing, fibre spinning and porous media (among others), present strongly extensional components that can significantly deform the fluid microstructure, resulting in elongation of polymeric constituents and orders-of-magnitude increases in elastic and normal stresses. Such extensional effects can dominate a fluid's rheology, but are not probed by conventional torsional rheometers. I will present recent results demonstrating the use of a unique design of microfluidic cross-slot device to characterize the stagnation point extensional rheology of a variety of complex fluids and to probe the macromolecular dynamics and fluid microstructural modifications using optical techniques. Model dilute solutions of closely monodisperse linear polymers in a theta solvent demonstrate how quantitative measurements of the flow field, macroscopic pressure drop and flow-induced birefringence in the cross-slot can provide a measure of the extensional viscosity and also enable estimates of macromolecular strain and analysis of the molecular weight distribution of the polymer sample. The same techniques can be applied to biological samples, and I will present preliminary results on hyaluronic acid solutions and human saliva, emphasising how such characterization could help improve therapies for conditions such as arthritis and oral mucositis. Finally, I will discuss the characterization of commercially and industrially relevant semi-dilute solutions of wormlike micelles, which display purely-elastic flow instabilities in the vicinity of the stagnation point.