This paper describes a poly(dimethylsiloxane) (PDMS) microfluidic device for measuring the viscosity of Newtonian fluids. The viscometer utilized the high solubility and permeability of air in PDMS to generate Poiseuille flow in the degassed PDMS microfluidic device. By measuring the distance the fluids traveled and the flow velocity in the PDMS microchannel, the ratio of the viscosity of the sample fluid to the viscosity of a reference fluid was determined, and the viscosity of the sample fluid was then obtained. Only 5 µL or less volume was consumed for the viscosity measurement. For most of the tested fluids, the results were in good agreement with the results from Ubbelohde viscometers, and the coefficients of variance were 3% or better. The wettability of the fluids on PDMS did not affect the measurement as the capillary forces were cancelled out in the data analysis. The PDMS viscometer was found applicable to a broad range of fluids, including aqueous solutions, non-PDMS-swelling organic solvents, fluorinated oil and blood plasma.

A poly(dimethylsiloxane) (PDMS) viscometer was developed to analyze the activity of endo-β-1,4-glucanases (EC3.2.1.4) on hydrolyzing sodium carboxymethylcellulose (NaCMC). In the viscometer, a PDMS pump was used as the vacuum source to drive the fluid flow in the PDMS microchannel. The numerical simulation by COMSOL suggested that the vacuum level of the PDMS pump increased during the viscosity measurement. The increasing vacuum level of the PDMS pump allowed more stable fluid flow than the constant vacuum of the conventional vacuum pump. By monitoring the fluids traveling in the microchannel, the viscosity of the endoglucanase-NaCMC solution was derived at different reaction times. The non-Newtonian behavior of the NaCMC solution was studied to ensure that the viscosity measurement was performed in the Newtonian range. A protocol was established to convert the viscometric activity to the activity of standard international units with Almin's method. The PDMS viscometer required only 20 μL sample for the endoglucanase assay and the results were in good agreement with the results from Ubbelohde viscometers.