Levich Institute Seminar
Tue, Mar 12
2:00 PM — 3:15 PM
Steinman Hall160 Convent Avenue
Steinman Hall, 312
Seminar by Professor Norman WagnerTITLE: Development of Microstructure/Rheology Relationships for Complex Fluids: Understanding Shear Banding in Polymer-like Micelles
ABSTRACT: Rheology with Morphology summarizes our goal for understanding the flow of complex fluids and the rational formulation of consumer products. In this lecture I will present results obtained on new instruments developed in our laboratory with collaborations at the Institute Laue Langevin (Grenoble, France), the National Center for Neutron Research at the National Institute of Standards and Technology, and TA Instruments. These instruments enable direct measurements of the microstructure governing the bulk rheological behavior of complex fluids. Cationic surfactants that self-assembly into viscoelastic, polymer-like micelles (PLM) can exhibit interesting flow anomalies such as shear banding as well as shear induced phase separation (SIPS). These instruments that exploit scattering methods during transient rheology, coupled with rheology and particle tracking velocimetry enable elucidating the molecular mechanisms underlying these rheological anomalies. Nonequilibrium state diagrams are constructed to connect the nonequilibrium behavior to the underlying equilibrium phase behavior. We also demonstrate how the combination of rheology, flow kinematics, and SANS measurements of flow-induced microstructure locally in the flow field can be used to critically evaluate constitutive equations for PLMs. I will also introduce the newly developed method of time resolved oscillatory rheology and small angle neutron scattering (tOR-SANS) and the time dependent morphology under large amplitude oscillatory shear (LAOS) and flow start ups. In particular, we demonstrate, for the first time, the microstructure development accompanying large amplitude oscillatory probing. These experiments provide a quantitative understanding of the nonlinear responses of the material under LAOS, which is a rapidly growing experimental method. These new instruments and analysis methods provide opportunities to rationally engineering complex fluids to meet specific performance requirements as well as new tools for fundamental scientific investigations.