The offered invention allows controlling the process of electrohydrodynamic (EHD) jet printing in which an ink is printed on a substrate as a continuous line or fiber, forming predesigned 2D patterns and 3D structures. This is also known as near-field electrospinning (NFES). The offered technology allows determining the speed at which the EHD ink jet approaches the substrate before it collects transforming into a printed fiber.
The knowledge of its speed of approach is critical for controlling the process of printing and create high-resolution patterns and structures, and, ultimately, for ensuring the desired performance of the printed fibers (device). In this invention, the jet trajectory is oscillated electrostatically at a known frequency, resulting in a repeating printed pattern. The speed is obtained from macroscopic, easily quantifiable features of the printed pattern, such as width on a serpentine track (2D pattern), or diameter of a cylinder (3D structure). A patent is pending for this technology.
The offered technology is a method for extending the current state of the art in electrohydrodynamic jet printing and near field electrospinning, toward higher resolution printing by means of continuous fibers as thin as a micron and smaller. Such thin fibers can be easily made by electrostatic pulling on a drop of ink, which ink has suitable conductive and rheological properties.
The process results in an ink jet moving at very high speed towards a substrate (even above 1 m/s). Conventionally, the printing is done by moving the substrate horizontally under the jet at high enough speed to match the speed of approach of the jet, resulting in a well-defined printed pattern. The ability to print a predefined pattern relies on knowing the speed at which the EHD ink jet approaches the substrate before it collects transforming into a printed fiber. However, this only works for slow jets (e.g. 0.01 m/s) as conventional mechanical stages move and accelerate too slowly to be able to control the jet's landing position. Instead, the offered technology uses electrostatic deflection of the jet without having to move the substrate at such high speed.
This technology allows determining the speed at which the EHD ink jet approaches the substrate by deflecting the jet repeatedly by means of the electric field created by auxiliary electrodes. The speed is obtained from macroscopic, easily quantifiable features of the printed pattern. For example, if the substrate is moved orthogonally to the plane of jet deflection, a track made of a repeating motif is produced, and the speed of the jet can be calculated from the measured width of a printed track and the frequency of the jet deflecting signal. In another example, the stage is not moving and a 3D structure, such as a cylinder, is produced. In this case, the jet speed can be calculated from the measured width of the printed structure and the frequency of the jet deflecting signal.
There is no need for the substrate to move at high speeds, or even to move. Nor is there a need to resolve the diameter of an individual fiber to surmise the length of fiber being printed in a time interval. The method works when the frequency is high enough so that the jet does not buckle on approaching the substrate. The method determines the speed of the continuously printed jet, as well as the length of printed fiber. The method can also be used for precisely controlling the jet trajectory for producing high resolution printed patterns and high-speed jets.
By knowing its speed, it becomes possible to position the fiber precisely onto the substrate to produce predefined high-resolution pattern. This approach enables manufacture of fiber tracks with predefined anisotropic properties (e.g., electrical, optical or wetting properties). This method is advantageous as it does not rely on imaging of individual printed fibers (which is laborious and requires expensive microscope and cannot generally be done in-situ during printing) and instead can be done by straightforward optical equipment such as camera. This method can be automated by image recognition (pattern recognition) software to enable in-situ monitoring and control of the printing process. The proposed method also can be used to detect jet speed instabilities in situ.
Benefits:
Allows well defined printing of patterns using a continuous fiber.
Allows quantification of printed fiber speed and printed fiber length for printing predefined 2D patterns and 3D microstructures.
Can be practiced in-situ, eliminating the need to calibrate printing parameters before or after the printing process.
Cheap, fast, reliable method, which does not require imaging of individual fibers.
Can be integrated with image recognition software to automate the printing process.
Applications
Printing of continuous fiber for flexible electronics, electrohydrodynamic printing, high resolution 3D printing, near-field electrospinning (NFES), melt electrowriting (MEW), electrospinning
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