Executive Summary : | Various macroscopic rheological measurement methodologies of complex fluids have been proposed and demonstrated till date – these devices are usually extremely expensive since they require the application of very minute kinematic conditions on the fluid of interest. Macroscopic rheometric measurements rely on simplifying flow kinematic conditions to impose simple kinematic conditions such as purely extensional or shear flow. The enabling transducers and motors can be expensive to build, maintain and control. Recent work from groups including that of the PI has demonstrated that simple events such as droplet coalescence can bear the signature of rheological properties of a complex fluid. This fact when utilized can enable researchers to measure fluid’s relaxation time without the need for very expensive rheometers. Since droplets of complex fluid are only involved, miniaturization also becomes possible allowing researchers to collect substantial data while integrating various sensors to the same platform. The field of microfluidics bears strong promise in this respect as microfluidic devices can be easily designed to mimic the micron-sized features that are found in many industrial and natural systems. These devices can be fabricated in an affordable and scalable manner and they require only small sample volumes and allow the experimentalist to impose large deformations in specially designed geometries. Moreover, microfluidics allows probing rheological sensitivity to interfacial conditions, exploring dependence of stress-strain constitutive relationships in complex geometries amongst others. In this context, this proposal explores the potential of microfluidic rheometry or rheometry-on-a-chip using a tiered approach. In the first tier, a simple microfluidic architecture will be employed to investigate coalescence of complex fluid droplets, where the coalescence kinematics can provide insight into a fluid’s characteristic relaxation time-scale. In the second tier, the device will allow for simultaneous flow kinematics quantification using micro-particle image velocimetry (µ-PIV). Such quantification will allow for the first time to probe rheological properties along with complex flow kinematics simultaneously. |