Mini-Portable Rheometer: A device for the on-site rheological characterization of viscoelastic fluids

Abstract

The on-site rheological characterization of complex fluids is important for a number of industrial, medical, and academic applications. Typically, laboratory-based rheometers are used to characterize rheological properties of fluids, which include, elasticity, relaxation time, and shear viscosity. However, this can be challenging as some samples, in particular biological fluids, may degrade over time and therefore do not retain their natural properties after collection and transport. In preparation for a human subject study, we investigated protocols to collect and preserve mucosalivary samples collected in a clinical location. Preliminary investigation and previous literature evidenced that mucosalivary fluid degraded with time as a result of protease and enzymatic activity on mucin polymers which contribute to the fluids bulk rheological properties. Therefore, we found it necessary to develop a portable, economical rheometer that can provide rapid results in the field. First, we investigated the sensitivity of capillary breakup measurements, the method chosen for measuring elasticity, to initial stretch parameters in using the commercial, Capillary Breakup Extensional Rheometer (CaBER), using analog polymer solutions. Finally, our study highlighted the need to measure elastic properties directly on site. This aided in determining the appropriate stretching parameters for characterization of biological fluids such as mucosalivary fluid without the effect of degradation and additionally with the ability to tune the rheological properties of fluids. We built a portable device for measuring elasticity using two modes: 1) direct imaging of the fluid capillary breakup and 2) an integrated electrical circuit to measure breakup time. The results showed that our portable device had comparable performance to the laboratory rheometer, CaBER.