Superposition 'Chirp' Rheometry: a new technique for the rapid rheological characterisation of complex fluids with transient microstructures.

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The flow and deformation properties (i.e. the Rheology) of complex fluids, which arise due to the fluids microstructure, are often a critical factor in achieving a product functionality. In this context, "products" may range from printed electronic components manufactured using functional inks, to the 'biological products' of physiological processes such as blood coagulation - i.e. the blood clot. However, the effect of complex flow conditions (which are inherent to the 'process') on the fluid microstructure, and hence flow properties, is difficult to study - especially if the process is dynamic (e.g. where the sample is undergoing curing, gelation, clotting, drying etc). This research proposal aims to develop, test and demonstrate a novel technique for characterising changes in the rheology (and microstructure) of flow-sensitive complex fluids occurring in response to a flow condition. It is proposed to develop a technique which uses 'chirp' waveforms (i.e. frequency modulated waveforms) to probe the time-dependent flow and deformation properties of fluids as they are experiencing flow. Successful delivery of the project will provide industrial and academic rheologists, product formulation specialists, manufacturers and process designers with (i) an extremely powerful tool for rapidly characterising rheological/microstructural changes occurring in response to a sustained shear flow, (ii) new insights into the microstructural consequences of gelation under unidirectional stress, and (iii) a framework for interpreting parallel superposition rheometric data.