چکیده (انگلیسی):

The purpose of this work was to measure viscosity of fluids
at low microliter volumes by means of quartz crystal impedance
analysis. To achieve this, a novel setup was designed
that allowed for measurement of viscosity at volumes of 8 to
10 μL. The technique was based on the principle of electromechanical
coupling of piezoelectric quartz crystals. The
arrangement was simple with measurement times ranging
from 2 to 3 minutes. The crystal setup assembly did not
impose any unwanted initial stress on the unloaded quartz
crystal. Quartz crystals of 5- and 10-MHz fundamental frequency
were calibrated with glycerol-water mixtures of
known density and viscosity prior to viscosity measurements.
True frequency shifts, for the purpose of this work,
were determined followed by viscosity measurement of
aqueous solutions of sucrose, urea, PEG-400, glucose, and
ethylene glycol at 25°C ± 0.5°C. The measured viscosities
were found to be reproducible and consistent with the values
reported in the literature. Minor inconsistencies in the measured
resistance and frequency shifts did not affect the results
significantly, and were found to be experimental in origin
rather than due to electrode surface roughness. Besides, as
expected for a viscoelastic fluid, PEG 8000 solutions, the
calculated viscosities were found to be less than the reported
values due to frequency dependence of storage and loss modulus
components of complex viscosity. From the results, it
can be concluded that the present setup can provide accurate
assessment of viscosity of Newtonian fluids and also shows
potential for analyzing non-Newtonian fluids at low microliter
volumes.