the wagner group















Scattering

Scattering and optical methods provide unique access to the length and time scales relevant for most complex fluids and colloidal materials. Our labs house several instruments for such methods for materials at rest and under shear, including:

- Brookhaven ZetaPALS (dynamic light scattering/electrophoretic mobility)
- Rheometrics Rheo-Optical Analyzer (flow-birefringence)
- Rheometrics ARES OAM (rheo-birefringence/dichroism)
- Bohlin Rheo-SALS device (rheo-light scattering)

Combining rheology with structural measurements such as those by scattering methods is a particularly powerful approach to understanding the behavior of fluids under flow. In addition to the above capabilities, our group has developed several methods for simultaneous measurement of structure and rheology under shear.

Small angle light scattering

In collaboration with TA instruments, we have designed a device for simultaneous small angle light scattering (SALS) and rheological measurement. This allows for rich characterization of the structure and dynamics of shear-induced structuring of a variety of fluids. Some features of the device include:

- Peltier temperature control

- Reliable optical focusing

- Synchronized data acquisition

- Streamlined data support

Small angle neutron scattering

Small angle neutron scattering (SANS) is a powerful technique for probing the microstructure of many of the complex materials we study in the Wagner group. Due to the ability of neutrons to penetrate materials which light and other radiation cannot, SANS allows measurement of the structure of materials under flow using existing rheometric devices. This ability enables unique possibilities for studying the microstructure of complex materials under a variety of flow conditions.

In a longstanding collaboration with the NIST Center for Neutron Research, we have developed a short gap Couette shear cell for SANS measurements under shear in the flow-gradient (1-2) deformation plane. Measurements in this plane provide several advantages over measurements in other deformation planes, including the ability to measure both structural alignment and orientation in the same measurement. Furthermore, the ability to collimate the incident neutron beam to as small as a 0.1 mm slit allows for spatially-dependent structural measurement across the shear gradient, which is particularly useful for materials which display inhomogeneous flow fields such as yielding, wall slip, and shear banding. To learn more about the 1-2 plane flow-SANS cell, please read our recent article in Physical Review E.