Modeling Electrical Double-Layer Effects for Microfluidic Impedance Spectroscopy to 110 GHz
Charles A. Little, Nathan D. Orloff, Christian J. Long, James C. Booth
Complex impedance measurements of fluids provide unique electrical information with important applications for chemical and pharmacological synthesis, and medical diagnostics. Many relevant fluids are ionic. During electrical measurement, ions in the fluid-under-test migrate to the electrodes, creating an electrical double-layer. Here, we model the electrical double-layer and complex permittivity response from 100 kHz to 110 GHz. Our measurements use integrated microfluidic coplanar waveguide devices to obtain the complex permittivity and conductivity of saline solutions at varying concentrations and temperatures. By modeling the frequency response of the double-layer, we extract a characteristic time constant for the effect which is linearly dependent on the conductivity of our saline solutions and electrode geometry. We demonstrate that the double-layer effects dictate a lower bound frequency limit for complex permittivity measurements, which can be estimated from the measured permittivity and conductivity of the fluid, the electrode geometry, and the diffusion coefficient of the ionic species. Knowing this allows for the design of microfluidic-microelectronics with tailored sensitive to either the complex permittivity or electrode polarization effects over the broadest frequency range possible.
, Orloff, N.
, Long, C.
and Booth, J.
Modeling Electrical Double-Layer Effects for Microfluidic Impedance Spectroscopy to 110 GHz, Lab on A Chip, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=922321
(Accessed March 3, 2024)