ABSTRACT
-Micropumps have attracted considerable interest in micro-electro-mechanical systems (MEMS), microfluidic devices, and biomedical engineering to transfer fluids through capillaries. However, improving the sluggish capillary-driven flow of highly viscous fluids is critical for commercializing MEMS devices, particularly in underfill applications. This study investigated the behavior of different viscous fluid flows under the influence of capillary and electric potential effects. We observed that upon increasing the electric potential to 500 V, the underfill flow length of viscous fluids increased by 45% compared to their capillary flow length. To explore the dynamics of underfill flow under the influence of an electric potential, the polarity of highly viscous fluids was altered by adding NaCl. The results indicated an increase of 20-41% in the underfill flow length of highly viscous conductive fluids (0.5-4% NaCl additives in glycerol) at 500 V compared to that at 0 V. The underfill viscous fluid flow length improved under the electric potential effect owing to the polarity across the substance and increased permittivity of the fluid. A time-dependent simulation, which included a quasi-electrostatic module, level set module, and laminar two-phase flow, was executed using the COMSOL Multiphysics software to analyze the effect of the external electric field on the capillary-driven flow. The numerical simulation results agreed well with the experimental data, with an average deviation of 4-7% at various time steps for different viscous fluids. Our findings demonstrate the potential of utilizing electric fields to control the capillary-driven flow of highly viscous fluids in underfill applications.
ABSTRACT
In the field of soft electronics, high-resolution and transparent structures based on various flexible materials constructed via various printing techniques are gaining attention. With the support of electrical stress-induced conductive inks, the electrohydrodynamic (EHD) jet printing technique enables us to build high-resolution structures compared with conventional inkjet printing techniques. Here, EHD jet printing was used to fabricate a high-resolution, transparent, and flexible strain sensor using a polydimethylsiloxane (PDMS)/xylene elastomer, where repetitive and controllable high-resolution printed mesh structures were obtained. The parametric effects of voltage, flow rate, nozzle distance from the substrate, and speed were experimentally investigated to achieve a high-resolution (5 µm) printed mesh structure. Plasma treatment was performed to enhance the adhesion between the AgNWs and the elastomer structure. The plasma-treated functional structure exhibited stable and long strain-sensing cycles during stretching and bending. This simple printing technique resulted in high-resolution, transparent, flexible, and stable strain sensing. The gauge factor of the strain sensor was significantly increased, owing to the high resolution and sensitivity of the printed mesh structures, demonstrating that EHD technology can be applied to high-resolution microchannels, 3D printing, and electronic devices.
ABSTRACT
This study addressed the dynamics of capillary-driven flow for different surface wettabilities by concentrating on the influence of electric potential. The capillary flow dynamics were investigated by varying the wettability (plasma-treated, hydrophobic, hydrophilic, and superhydrophilic) of a capillary surface, and the applied electric potential to the liquid ranged from 0 to 500 V. When an electric potential was applied to the liquid, the fluid flow penetration length increased by 30-50% due to the electrohydrodynamic (EHD)-driven flow by the Maxwell (electric) pressure gradient effect. The results showed that the EHD effect enhanced the fluid penetration through narrow gaps. The maximum fluid penetration was attained for every surface at 500 V, particularly for the superhydrophilic surface, which exhibited the highest value. The combined effect of the electric field and wettability resulted in an enhanced fluid penetration speed, reducing the underfill time. In addition, theoretical and numerical models were developed for comparison with the experimental results. The proposed models reinforce the observed fluid flow phenomenon on various surfaces under the influence of an electric field. These findings can provide alternative strategies for controlling the dynamic features of capillary imbibition by introducing an electric field and wettability effects, which has practical implications in flip-chip packaging, microfluidic devices, and the manipulation of biocells.
