New insight into rheology and flow properties of complex fluids with Doppler optical coherence tomography

Flow properties of complex fluids such as colloidal suspensions, polymer solutions, fiber suspensions and blood have a vital function in many technological applications and biological systems. Yet, the basic knowledge on their properties is inadequate for many practical purposes. One important reason for this has been the lack of effective experimental methods that would allow detailed study of the flow behavior of especially opaque multi-phase fluids. Optical Coherence Tomography (OCT) is an emerging technique capable of simultaneous measurement of the internal structure and motion of most opaque materials, with high spatial and temporal resolution. For the first time a rheometer augmented with OCT reveals whether the rheometer measurement actually represents true material properties of the suspension or if the data is merely reflecting boundary layer phenomena. This will be essential new information for many materials and improve current material and flow models for these rheologically complex materials. In this work OCT data is also combined with Pulsed Ultrasound Doppler Velocimetry (PUDV) and magnetic resonance imaging (MRI) to study industrially relevant flow geometries. This enables a detailed study of the rheology of complex fluids in process flow environment where the behavior of the material (e.g. cellulose micro fibrils) is not restricted by the system size.