Viscosity imaging by fluorescent molecular rotor for polymer-solution flow around microstructures

To understand the complex behavior of polymer solution flow and biological flow, such as blood flow, it is important to quantify the shear viscosity distribution that changes with the shear rate in a flow channel. In this study, we focused on 9-(2,2-dycyanovinyl)julolidine (DCVJ), a fluorescent molecular rotor that shows the variation in the fluorescent intensity depending on the viscosity. This study aims to demonstrate the efficiency of DCVJ for imaging the shear viscosity distribution of viscoelastic fluids.

First, DCVJ was dissolved in several aqueous glycerol solutions of different concentrations, and a calibration curve was determined by obtaining the relationship between viscosity and fluorescent intensity. Then, the fluorescent intensity distribution of the DCVJ-dissolved polyacrylamide-solution flow around the triangle-shaped micropillars in a microchannel was obtained. The viscosity distribution around the micropillars was determined from the intensity distribution and the calibration curve, and the non-uniform viscosity distribution appeared because the solution has shear-thinning property. Subsequently, the shear-rate distribution was obtained from the velocity distribution and compared with the shear viscosity distribution.