Development of microfluidic viscometer based on electrofluidic pressure sensor
Date Issued
2016
Date
2016
Author(s)
Lee, Tse-Ang
Abstract
Rheological properties, viscosity, are important in biomedical applications. For instance, the viscosity of body fluids such as blood, saliva or urine have been linked with health condition. A microfluidic viscometer is designed and constructed in this thesis in order to investigate the viscosity of biological and biomedical samples, including Newtonian and non-Newtonian fluids, where large sample volume is not available and disposability of the device is desired. The developed pressure sensing component can be seamlessly fabricated into polydimethylsiloxane (PDMS) microfluidic systems using the well-developed multilayer soft lithography (MSL) technique without additional assembly or sohisticated cleanroom microfabrication processes. Viscosity can be obtained through the flow resistance, ratio of the pressure change to the corresponding variation of flow rate, for Newtonian fluids. For determination of non-Newtonian fluids, an additional parameter, power-law index is required besides flow resistance. A pressure sensor with an electrical readout based on electrofluidic circuits is constructed by ionic liquid-filled microfluidic channels. The pressure sensing is achieved by measuring the pressure-induced electrical resistance variation of the electrofluidic resistor. In addition, an electrofluidic Wheatstone bridge circuit is designed for accurate and stable resistance measurements. A syringe pump is used to control the flow rate. The power-law index of non-Newtonian fluids can be obtained through the slope in a log-log plot of the output voltage shift of the Wheatstone bridge versus the flow rate. Thus, the viscosity can be calculated by the related derivation. The microfluidic viscometer is able to measure viscosity from 1 cP to around 100 cP under a wide shear rate from 5s-1 to more than 1000s-1 with sample volume less than 0.4ml. In addition, the Wheatstone bridge arrangement possesses excellent thermal stability since the temperature fluctuation will be well compensated in the system. Consequently, the device can be easily scaled up with other microfluidic system and can be applied widely in applications where various temperature operations are required.
Subjects
Microfluidic viscometer
Electrofluidic circuit
Wheatstone bridge
Pressure sensor
Type
thesis
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