Micro/Nano-scale Direct Writing

Achieving high-resolution direct writing of micro and nano fibers for novel applications in sensor and composite fabrication.

Three-dimensional (3D) printing of micro/nano-scale structures with high resolution (sub-micron) and low cost is still a challenging work for the existing 3D printing techniques. Near-field electrospinning and near-field melt electrospinning is a viable technique to overcome existing limitations.

For example, in near-field melt electrospinning, a molten polymer jet is ejected from the needle tip and stabilized in the near-field region (several millimeters) subjected to an external high voltage. Then the molten jet is collected in a defined pattern on the substrate and solidifies. The process allows continuous direct writing due to the linear and stable jet trajectory in the electric near-field. The layer-by-layer stacking of fibers, or self-assembly effect, is attributed to the attraction force from the molten deposited fibers and accumulated negative charges.

We have explored the process control strategy using external electric fields to steer the polymer jet (You et al., 2020) (You et al., 2017). We demonstrated micro-scale 3D printing using near-field melt electrospinning (You et al., 2017). Recently, we explored the immersed electrohydrodynamic direct writing to achieve near field-electrospinning inside a liquid bath, so fiber morphology and registration can be controlled to direct print fiber-reinforced composites (Xu et al., 2023) (Xu et al., 2022).

References

2023

Fabrication of fiber-reinforced composites via immersed electrohydrodynamic direct writing in polymer gels

Yunzhi Xu , Nathanial Buettner , and Ping Guo

MRS Communications, Oct 2023

Abstract PDF Video

Fiber-reinforced composites have provided tremendous opportunities in advanced engineering materials, but the fiber generation and spatial distribution are the most challenging aspects. This paper proposes a novel fabrication approach for fiber-reinforced composites with spatially resolved fiber distribution by combining immersion and near-field electrospinning. The new Immersed Electrohydrodynamic Direct-writing (I-EHD) process makes use of an electrostatic force to draw ultrafine fibers and allows the freestanding of electrospun fibers all inside a liquid matrix. This novel approach enables the dynamic control of fiber morphology and 3D spatial distribution inside the composites, which may lead to future scalable 3D printing of multifunctional composites.

2022

Fabrication of fiber-reinforced polymer ceramic composites by wet electrospinning

Yunzhi Xu , Junior Ndayikengurukiye , Ange-Therese Akono , and Ping Guo

Manufacturing Letters, Oct 2022

Abstract PDF

We propose a novel approach of wet electrospinning to yield fiber-reinforced polymer ceramic composites, where a reactive ceramic precursor gel is used as a collector. We illustrate our approach by generating polyethylene oxide (PEO) fibers in a potassium silicate gel; the gel is later activated using metakaolin to yield a ceramic-0.5 wt% PEO fiber composite. An increase of 29% and 22% is recorded for the fabricated polymer ceramic composites in terms of indentation modulus and indentation hardness respectively. Our initial findings demonstrate the process viability and might lead to a potentially scalable manufacturing approach for fiber-reinforced polymer ceramic composites.

2020

Fabrication of Microscale Polymeric Wavy and Coiling Structures via Side-Electrode-Assisted Near-Field Electrospinning: Modeling and Experiments

Xiangyu You , Yang Yang , and Ping Guo

Journal of Manufacturing Science and Engineering, Oct 2020

Abstract PDF Video

It is challenging for the existing fabrication strategies to generate microscale wavy and coiling structures with low cost and high efficiency. In this work, we develop a novel and simple method that allows the fabrication of microscale wavy and coiling fiber arrays via near-field electrospinning (NFES). In addition to the main vertical electric potential for polymer jet generation, additional electrostatic signals are applied to the side-auxiliary electrodes to dynamically control the fiber deposition. Compared with traditional electrospinning based on the buckling instability or mechanical collector movement, the proposed method shows advantages in terms of the controllability, stability, accuracy, and minimal feature size. A theoretical model to describe the polymer jet behaviors has been proposed to simulate the fabrication process by considering the momentum balance of viscoelastic, charge repulsive, and electric forces. The model has been directly verified through the comparison with experimental results. The effects of different process parameters on the fiber deposition patterns are analyzed and discussed. The processing capability has been further demonstrated by fabricating two-dimensional wavy and coiling patterns as well as three-dimensional wavy structures with the radius of curvature less than 100 µm.

2017

Electric field manipulation for deposition control in near-field electrospinning

Xiangyu You , Chengcong Ye , and Ping Guo

Journal of Manufacturing Processes, Oct 2017

Abstract PDF

Electrospinning is recognized as an efficient and versatile technique that has been widely used in nanoscale fiber fabrication. Electric field manipulation is one of the efficient ways to precisely control an electrospinning jet. While there have been several studies of the electric field manipulation effect on nanofiber deposition control, these works are limited to the control of a far-field electrospinning (FFES) jet to deposit in one dimension or to suppress the chaotic whipping mode to some extent. Few work has been done to control a near-field electrospinning (NFES) jet for deposition of complex patterns using electric field manipulation. To this end, we propose a novel design by adding a moving sharp-pin electrode beneath the plane collector. The sharp pin electrode is charged with a positive voltage and moved to redistribute the electric field for jet trajectory control, while the plane collector is kept stationary. The focusing of the electric field and the guiding effect of the jet trajectory due to the additional sharp-pin electrode are studied and demonstrated. Various parameters (voltage, electrode translation speed, and collection mechanism) are analyzed to experimentally study their effects on the fiber deposition control. It is demonstrated in the current work the feasibility of controlling a single fiber for deposition of complex patterns in near-field electrospinning by manipulating the electric field distribution.
Study of Microscale Three-Dimensional Printing Using Near-Field Melt Electrospinning

Xiangyu You , Chengcong Ye , and Ping Guo

Journal of Micro and Nano-Manufacturing, Oct 2017

Abstract PDF

Three-dimensional (3D) printing of microscale structures with high-resolution (submicron) and low-cost is still a challenging work for the existing 3D printing techniques. Here, we report a direct writing process via near-field melt electrospinning (NFME) to achieve microscale printing of single filament wall structures. The process allows continuous direct writing due to the linear and stable jet trajectory in the electric near field. The layer-by-layer stacking of fibers, or self-assembly effect, is attributed to the attraction force from the molten deposited fibers and accumulated negative charges. We demonstrated successful printing of various 3D thin-wall structures with a minimal wall thickness less than 5 μm. By optimizing the process parameters of NFME, ultrafine poly (ε-caprolactone) (PCL) fibers have been stably generated and precisely stacked and fused into 3D thin-wall structures with an aspect ratio of more than 60. It is envisioned that the NFME can be transformed into a viable high-resolution and low-cost microscale 3D printing technology.