Combining Small-Angle Neutron Scattering (SANS) with a deformation field to probe structures under flow has led to significant advances in our understanding of complex fluids. Using a modified rheometer with a Couette cell which allows simultaneous rheological and structural measurements in the flow-vorticity (1-3 plane) and shear gradient-vorticity (2-3 plane) planes where the incident beam is parallel to the shear gradient and to the flow direction respectively, information on the material microstructure during the shear have been reported on dispersion of acicular nanoparticles, wormlike micelle, and membrane phases. Although use of this geometry to probe structural changes under shear flow has had remarkable success, the most important changes in fluid microstructures often occur in the 1-2 (flow-shear gradient) plane and cannot be accessed in this way. We have developed a new, prototype Couette shear cell that allows measurements in the 1-2 plane with the additional ability of resolving position within the gap separation as the incident beam is parallel to the vorticity direction. The possibility to access spatial resolution in the gap is essential for resolving shear-induced phase separation. This is a unique capability as the other two configurations available with the standard Couette cell (radial and tangential) probe the average structure through the gap. The prototype cell has already been successfully used in the case of worm-like micelle and cubic phases under flow where degree of structural anisotropy and direction of the anisotropy can be determined. Using this new capability along with more standard scattering techniques, including light scattering, we are developing a program to take a fresh look at a variety of complex fluids known to be altered by shear, particularly those that exhibit shear-induced transitions of various descriptions.

 

key words

1-2 shear plane; Colloid; Complex fluids; Neutron scattering; Shear; Shear-induced phase transition; Small-angle scattering; Surfactant;

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral applicants