(209f) Extending the Rheological Characterization of Complex Fluids into the High Frequency and High Shear Rate Regime through Optical Microrheology and Microfluidic Flows

Complex fluids are ubiquitous across a range of industrial and consumer sectors, with common examples being inks, paints, drilling fluids, cosmetics, personal care products and foodstuffs. The processing and product functionality attributes of such materials are often dependent on their rheological response and are inherently linked to the underlying microstructure, specifically in relation to the relevant process time or rate. Since microstructural rearrangement can occur on different length scales and over a wide range of timescales, multiple rheometric techniques are often required to fully characterise the material response. For example to evaluate the properties of an inkjet formulation in relation to its jetting performance, the behaviour at high frequency (short timescales) and high shear rate is most critical. For evaluating product stability attributes and resistance to sedimentation of the same ink formulation, its behaviour at low frequencies (long timescales) and shear rates (or stresses) is most relevant .

In relation to the above, the use of polymer solutions as model complex fluids has been studied using a combination of rotational rheometry, DLS microrheology and microfluidic flows in order to establish material behaviour over multiple decades of shear rate and timescale. The complementary benefits of these techniques are discussed with specific focus on the unique insights that each can offer in enabling the characterization of the dynamics of the material response (flow and viscoelasticity) under process-relevant conditions.