In the inkjet printing process, the core of stable Taylor cone jetting controlled by an electric field lies in precisely controlling the dynamic balance between the electric field force and the surface tension and viscosity of the fluid to achieve accurate droplet generation and directional deposition. This process involves multiple stages, including electric field construction, Taylor cone formation, jet breakup, and droplet control, and its stability directly determines the printing resolution and pattern quality.
In the electric field construction stage, the inkjet printing system applies a high-voltage electric field between the nozzle and the substrate, causing polarized charges to form on the conductive ink surface at the nozzle tip. These charges form a tangential electric force under the influence of the electric field, driving the droplet surface to stretch and deform. When the electric field force and the ink surface tension reach equilibrium, the droplet gradually contracts from a hemispherical meniscus into a cone shape, forming a Taylor cone. At this point, the stability of the Taylor cone depends on the matching of the electric field strength and the ink properties: if the electric field is too weak, surface tension dominates, and the Taylor cone cannot be maintained; if the electric field is too strong, it may cause multiple jets or droplet splashing.
The Taylor cone formation process consists of two stages: energy storage and jetting. During the energy storage phase, the droplets oscillate repeatedly under the influence of the electric field and surface tension, gradually accumulating charge and adjusting their cone angle. The duration of this phase is influenced by voltage intensity, ink viscosity, and surface tension. For example, high-viscosity inks require a longer time to accumulate charge, while low-surface-tension inks are prone to uneven charge distribution, leading to a tilted Taylor cone. When the electric field exceeds a critical value, the charge density at the tip of the Taylor cone reaches its peak, and the electric field instantly overcomes the surface tension, forming a continuous jet. Initially, the jet is straight, but subsequent solvent evaporation increases the electrostatic repulsion between charged particles, causing the jet to split into tiny droplets.
The stability of the jet's breakup is a key challenge in electric field control. If the electric field distribution is uneven, the jet may break up prematurely due to excessively high local charge density, forming satellite droplets; if the electric field strength is insufficient, the jet may fail to break up due to viscous forces, resulting in excessively large droplet sizes. To address this issue, modern inkjet printing systems optimize nozzle structure (e.g., using conical or stepped nozzles) and electric field distribution (e.g., employing a non-uniform electric field) to achieve uniform jet fragmentation. Furthermore, by adjusting the voltage pulse frequency and duty cycle, the droplet generation frequency can be controlled, preventing droplet overlap or gaps.
The directional deposition of droplets relies on the electric field's control over the trajectory of charged droplets. During the jetting phase, droplets carrying charge move within the electric field, their trajectory determined by the field strength and direction. Precise droplet positioning in three-dimensional space can be achieved by adjusting the substrate potential or using a multi-electrode array. For example, in flexible electronics manufacturing, dynamically controlling the electric field distribution allows for the deposition of uniform conductive lines on curved substrates, avoiding pattern fragmentation caused by substrate deformation in traditional inkjet technology.
Ink properties significantly affect the stable jetting of Taylor cones. Excessively high viscosity leads to poor ink flow, making it difficult to form a stable Taylor cone; excessively low viscosity may reduce print resolution due to easy ink diffusion. Excessive surface tension increases the demand for electric field force, leading to increased energy consumption; conversely, insufficient surface tension may cause excessive ink spreading on the substrate, resulting in a "coffee ring" effect. Therefore, ink composition must be adjusted according to printing requirements, such as adding surfactants to regulate surface tension or using nanoparticles to thicken and increase viscosity.
A real-time feedback mechanism for electric field control is crucial for maintaining stable Taylor cone jetting. Modern inkjet printing processes integrate high-speed cameras and sensors to monitor the Taylor cone morphology and droplet formation state in real time, feeding this information back to the electric field control system. When Taylor cone tilt or abnormal droplet size is detected, the system automatically adjusts voltage parameters or nozzle position to restore stable jetting. For example, in 3D microstructure printing, closed-loop control can achieve layer-by-layer deposition accuracy compensation, ensuring the final structure meets design requirements.
From an application perspective, electric field-controlled Taylor cone stable jetting technology has been widely used in flexible electronics, biosensors, and optical device manufacturing. In the fabrication of flexible pressure sensors, this technology can deposit silver electrodes at the 10μm level, achieving high sensitivity and bend resistance. In the preparation of electrochemical sensors, by constructing a micro three-electrode system layer by layer, detection accuracy and stability can be improved. With the advancement of materials science and electric field control technology, the inkjet printing process is breaking through traditional size limitations and evolving towards nanoscale precision and multifunctionality.
