Neutron scattering of complex fluids in simple and complex flows

Abstract

This thesis reports the coupling of microfluidics and small angle neutron scattering (SANS) for the study of model complex fluids, in particular the phase mapping of surfactant mixtures and colloidal dispersions. Microfluidics provides an exceptionally well controlled environment for the handling of fluids, enabling precise formulation across the phase space of mixtures under equilibrium conditions. SANS is a unique experimental probe for matter at the molecular to mesoscopic lengthscales, and the advent of microfluidic-SANS, made possible by judicious microfabrication materials and methods, opens up a range of novel and powerful research avenues to probe complex fluids under equilibrium and non-equilibrium conditions. This work focuses on establishing the capabilities and limitations of microfluidic-SANS for the phase mapping of complex fluids. During the initial stages of the project, we selected and manufactured SANS compatible microdevices, and identified the experimental conditions for optimal screening of fluids, considering device geometry, SANS spectrometer and beam characteristics, and operation of the system. We demonstrated the first microfluidic-SANS contrast matching experiment, a key type of neutron scattering experiment, as it enables the direct determination of molecule (and aggregate or assembly) shape and composition in both dilute and dense media. The approach is validated by comparing the results to the ones obtained with standard techniques. Both continuous and segmented flows were evaluated and compared in terms of reliability and compatibility with SANS techniques. Ternary and quaternary surfactant solutions were studied and innovative data analysis approaches established. We expect that microfluidic-SANS will bring a paradigm shift in routine SANS operation, as well as open routes for unprecedented flow-induced and kinetic interrogation of soft and biological matter.