Microfluidic Electrochemical Impedance Spectroscopy of Carbon Composite Nanofluids

Abstract

Understanding the internal structure of composite nanofluids is critical for controlling their properties and engineering advanced composite nanofluid systems for various applications. This goal can be made possible by precise analysis with the help of a systematic robust platform. Here, we demonstrate a microfluidic device that can control the orientation of carbon nanomaterials in a suspension by applying external fields and subsequently examine the electrochemical properties of the fluids at microscale. Composite nanofluids were prepared using carbon nanomaterials, and their rheological, thermal, electrical, and morphological characteristics were examined. The analysis revealed that microfluidic electrochemical impedance spectroscopy (EIS) in the device offered more reliable in-depth information regarding the change in the microstructure of carbon composite nanofluids than typical bulk measurements. Equivalent circuit modelling was performed based on the EIS results. Furthermore, the hydrodynamics and electrostatics of the microfluidic platform were numerically investigated. We anticipate that this microfluidic approach can serve as a new strategy for designing and analyzing composite nanofluids more efficiently.

Figure 1

(A) 3-D schematic illustration of the microfluidic device and (B) top-view image of the device with the embedded gold electrodes.

Figure 2

Numerical analyses for the microfluidic device: (A) electric field distribution and (B) flow field distribution. The dashed lines indicate the positions of the gold electrodes.

Figure 3

(A) UV-visible absorption spectra of the samples, (B) size distribution of sample 2, (C) AFM results of dispersed graphite. The scale bar indicates 5 μm.

Figure 4

(A) Variation in the electrical and thermal conductivities for the samples and (B) shear viscosity of the samples as a function of the shear rate.

Figure 5

FESEM images of (A) sample 1, (B) sample 2, (C) sample 3, (D) sample 4, and (E) sample 5. The scale bar indicates 1 μm.

Figure 6

Impedance results of the bulk solution: (A) magnitude and (B) phase of the Bode plot.

Figure 7

Microfluidic impedance changes according to the applied potentials: (A) Bode plot of sample 2, (B) Nyquist plot of sample 2, (C) Bode plot of sample 3, and (D) Nyquist plot of sample 3.

Figure 8

Microfluidic impedance changes according to the applied flow fields: (A) Bode plot of sample 2, (B) Nyquist plot of sample 2, (C) Bode plot of sample 3, and (D) Nyquist plot of sample 3.

Figure 9

Equivalent circuit analysis: (A) equivalent circuit for microfluidic impedance fitting and (B) fitting results of sample 2 and (C) fitting results of sample 3.