Droplet Impact-Based Microliter Viscometry.

Characterizing liquid viscosity and rheological properties with small sample volumes is crucial in fields where liquid samples are often limited, such as biological fluids for biomedical diagnostics and trace chemical products. However, traditional viscometers often require large sample volumes, and many existing small-volume viscometry techniques fall short in analyzing non-Newtonian fluids due to their limited shear rate range. While microfluidics-based viscometers offer flexibility in shear rate control, they are generally associated with intricate fabrication processes and high costs. Here, we introduce a droplet impact-based microliter viscometry (DI-μV), building on a quantitative relationship between viscosity and the maximum spreading factor of droplets impacting super-repellent surfaces. Leveraging the sufficient viscous effect during droplet impact, DI-μV can measure effective viscosity across varying effective shear rates and probe the rheological properties of liquids, using only μL-scale volumes. As a tool for viscosity measurement, DI-μV exhibits minimal sample consumption, adjustable effective shear rate, self-cleaning capabilities, operational simplicity, and cost-effectiveness, thereby offering relevant practical implications.