Many materials in everyday life exhibit peculiar behaviour due to applied mechanical deformations. Rheo-NMR is an established technique which has been used for almost three decades to study these responses by combining methodology from rheometry and nuclear magnetic resonance [1-3]. It enhances standard rheological studies of bulk properties, such as viscosity and elasticity, by exploring the molecular origins and / or local responses within a material.
This contribution reports on the development and application of a novel geometry for magnetic resonance microscopy (MRM) – a planar-cylindrical hybrid (PCH) shear cell – to study fluid mechanics and the complex response of materials under shear. The geometry includes sections of planar Couette flow with the aim to provide a simple homogeneous shear profile. Various geometries to establish planar Couette flow have been used previously to study the fluid mechanics of simple fluids [4-6] but have never been developed for NMR. Generally, they are composed of two parallel sections of planar flow connected by two semicircular sections of circular flow to give a closed flow path in the shape of a racetrack. Shear is applied by rotating a band around the inner section like a conveyer belt. This is another step in recent efforts to enrich the Rheo-NMR toolbox by removing the inhomogeneous flow field conditions as generated by the concentric cylinder / Taylor-Couette (TC) geometries [7] (for which the narrow gap approximation is harder to satisfy as compared to in conventional rheometry).
Previous work on one shear banding wormlike micelle (WLM) solution demonstrated that the curvature of TC cells used during Rheo-NMR experiments influenced the observed rheological response [8]. This work further investigated the influence of curvature by studying the local dynamics of the WLM solution using the PCH in combination with a variant of the RARE pulse sequence [9]. Commonalities and differences of the WLM solution in the PCH when compared to simple fluid systems (e.g. silicone oil) and TC geometries will also be discussed.