Title: "Integrated experimental and modeling tools for probing microstructural changes of polymers and wormlike micelles under flow"
Abstract: Entangled polymers and surfactant-based wormlike micelles are widely used in both consumer products and oilfield applications. Flow processing of these materials usually involves nonlinear deformations, which can significantly modify both the associated microstructural configuration and dynamics. Determining the connection between processing, structure, and properties remains a grand challenge due to limitations in currently available tools.
Here, I present a comprehensive framework that combines experiments, simulations, and theories to characterize and predict microstructural changes in flow. First, we combine numerical calculations and a perturbation analysis using detailed microstructural models to study a recently advanced experimental technique, orthogonal superposition, for entangled polymers. We find that orthogonal superposition gives very useful information about nonlinear material moduli under flow, which can provide better sensitivity for testing constitutive models for nonlinear polymer processing.
Additionally, I apply these integrated tools to study if and how flow affects the scission and recombination of wormlike micelles (WLMs). Although it is widely accepted that equilibrium micelle scission dynamics greatly influences the rheology of WLMs, there is still considerable theoretical debate regarding whether scission dynamics is affected by flow under nonlinear deformations. We combine state-of-the-art flow-small angle neutron scattering (flow-SANS) measurements with anisotropic scattering predictions of deformable objects to provide direct structural evidence of flow-enhanced micellar scission, which offers crucial information for building more accurate rheological models of wormlike micelles. The new experimental and modeling tools developed in this study have broad applications in micellar fluids, polymers, and other deformable soft materials under nonlinear deformations.
Committee co-chairs: Prof. Matthew Helgeson and Prof. Gary Leal