Relative viscosity evaluation of low-volume samples using capillary flow under differential pressure

In this study, we newly considered the analysis of capillary flow under differential pressure, which extends the previous study and allows the independent measurement of relative viscosity and the product of relative surface tension and contact angle for low-volume samples. The theory of this method is explained, and it is demonstrated that relative viscosity and surface tension with contact angle can be obtained independently by measuring the capillary flow under differential pressure. We conducted capillary flow experiments with a small sample volume (less than 100 mu l) using a measurement system comprising a flow measurement unit, capillary chip, and differential pressure mechanism. The relative viscosities of pure water and dilute ethanol solutions obtained in the experiment were in one-to-one correspondence with the values in the Chemical Handbook. This also shows that relative surface tension can be determined using these measurement results and the separately measured contact angle values.