Helix Electrohydrodynamic Printing of Highly Aligned Serpentine Micro/Nanofibers

Abstract

Micro/nano serpentine structures have widespread applications in flexible/stretchable electronics; however, challenges still exist for low-cost, high-efficiency and controllable manufacturing. Helix electrohydrodynamic printing (HE-printing) has been proposed here to realize controllable direct-writing of large area, highly aligned serpentine micro/nanofibers by introducing the rope coiling effect into printing process. By manipulating the flying trajectory and solidification degree of the micro/nano jet, the solidified micro/nanofiber flying in a stabilized helical manner and versatile serpentine structures deposited on a moving collector have been achieved. Systematic experiments and theoretical analysis were conducted to study the transformation behavior and the size changing rules for various deposited microstructures, and highly aligned serpentine microfibers were directly written by controlling the applied voltage, nozzle-to-collector distance and collector velocity. Furthermore, a hyper-stretchable piezoelectric device that can detect stretching, bending and pressure has been successfully fabricated using the printed serpentine micro/nanofibers, demonstrating the potential of HE-printing in stretchable electronics manufacturing.

Investigation of dielectric properties of free standing electrospun nonwoven mat

“…demonstrated the development of hyperstretchable self‐powered piezoelectric nano/microfiber sensors with excellent mechanical and piezoelectric properties . The authors envisioned that such kind of materials and processing technique renders high stretchability and high sensitivity which can be a potential application in super artificial skin for humanoid robotics, human‐machine interfaces, and physiological analysis devices …”

Large‐Scale Direct‐Writing of Aligned Nanofibers for Flexible Electronics

“…It can produce droplets at least an order of magnitude smaller than the nozzle size, and complex patterns with high‐resolution as small as sub‐micrometer can be printed . EHD direct‐writing is a straightforward, cost‐effective and high‐efficient method to print fibers with diameters ranging from several micrometers to tens of nanometers (Figure d,g), which overlaps contemporary textile fiber technology . Electrospray utilizes electrical field to disrupt the liquid cone for liquid atomization (Figure e,h), and large area thin films in nanoscale thickness could be easily fabricated …”

“…g) The EHD direct‐written patterns of a spring‐like structure, a buckled heel or a stretched catenary under different substrate velocities. Reproduced with permission . Copyright 2017, MDPI AG.…”

“…Several science fictional events in popular culture that inspired subsequent critical technological advancements in the development of EHD direct‐writing have been emphasized. Reproduced with permission: “Electrostatic lens,” “Spring,” “Serpentine microstructures,” “High‐temperature melt based 3D printing,” “Alternating current induced wavy direct‐writing,” “Helix EHD Printing,” Copyright, respectively, 2001, 2007, 2012, 2013, 2015, 2017, MDPI AG. “Auxiliary electrodes,” “Near‐field electrospinning,” “Light‐emitting coaxial nanofibers,” Copyright, respectively, 2003, 2006, 2012, American Chemical Society.…”

“…The MES was able to fabricate straight fiber array with controlled diameter and position, orderly bead‐on‐string microstructures in a continuously tunable manner, and other sacrificial structures or polymer templates for micro/nanofabrication . Based on previous experimental researched on the fabrication of serpentine microstructures via electrospinning, Huang et al presented a mathematic illustration of this type of printing mode named HE‐Printing in 2017. It could individually manipulate the fiber flying in a helical manner and directly fabricate various serpentine nano/microfibers through a linear motion collector .…”