Nanoscale Diameters

Nanofibers with nanoscale diameters are attractive for their wide applications, ranging from envi ronment to energy, electronics, and health care. As the diameters of electrospun fibers are usually larger than 100 nm, several approaches, such as jet stretch enhancement, coreeshell or multicom ponent spinning, and spinning of extremely diluted solutions, have been proposed to further decrease the fiber diameter. However, the limited thinning capacity (usually >50 nm) and low production still remain. Electronetting, as a polymer processing technology, achieves the large-scale fabrication of 2D nanonet materials with nanoscale diameters. The average diameter of the interlinked nanowires in nanonets is about 10e30 nm, which is about 1 order of magnitude smaller than that of conventional electrospun fibers. For example, the major distribution region of nanowires in PAA nanonets reported by Wang and coworkers is 10e20 nm, while for PA-6 nanonets, each nanowire has a uniform diameter of w26 nm, as shown in Fig. 8.6. Benefiting from the extremely small diameter, the resultant nanonet membranes usually show enhanced surface area compared with the common electrospun nanofiber membranes. According to the results of

Foshan Lepton Precision M&C Tech Co.,Ltd Qualification Honor

Foshan Lepton Precision M&C Tech Co.,Ltd Qualification Honor

Foshan Lepton Precision M&C Tech Co.,Ltd Development History

In 2004, electrospinning research team was founded;

In 2006, first proposed Near-Field electrospinning theory;

In 2014, Foshan Lepton Precision M&C Tech Co.,Ltd was founded as the platform in electrospinning industrialization;

In 2016, got the High-tech Enterprise Certificate;

In 2017, the company's chief technical adviser was awarded "intelligent manufacturing star" in Foshan high-tech industrial development zone;

In 2018, it was listed as a warehousing technology enterprise in Guangdong province.

Foshan Lepton Precision M&C Tech Co.,Ltd Company Profile

        Based in Foshan National HighTech Industries Development Zone, Foshan Lepton Precision M&C Tech Co.,Ltd (Qingzi Nano) is a national hightech enterprise which dedicate to the research and development of electrospinning and eletrospraying printing techniques.  We manufacture, sale and provide technical support for electrospinning and electrospraying machines, electrospun nanofiber production line, bioscaffold 3Dprinter and nanofiber products.

         With our powerful and innovative research and development team, Qingzi Nano has established close cooperation with Nanyang Technological University, Xiamen University, Tsinghua University, Sun Yatsen University, South China University of Technology, Guangdong University of Technology and Jinan University. Our techniques and products have been widely applied in the field of environment, energy, electronics, biomedical etc. Our electrospinning products have been awarded as innovative hightech products.

        Qingzi Nano owns more than 80 patents, including over 50 patents for inventions on the techniques and equipment of electrospinning, bio-3D printing and electrospray printing.

Ion-Initiated Splitting of Electrospun Fibers

In 2009, another possible formation mechanism of 2D nanonets was proposed by Kim and coworkers, and they claimed that nanonets could be produced by tailoring the polar polymer solutions based on the inspiration of ionic salts. During the electrospinning process, high voltage allows the polymer solution to be charged and the resultant charge repulsion causes the solution to be deformed, forming the Taylor cone and its ejected jets. They thought that the formation of nanonets was attributable to the ions in the polymeric solution, and should occur at the place of formation of the main nanofibers. The nanonets can be considered as joints between the main fibers, and among the nanowires from the nanofibers, and between the nanowires and the nanofibers, which can be confirmed by transmission electron microscopy results, as shown in Fig. 8.4B and C. Taking into account the solvent evaporation process and randomly distributed state of the ions, the highly viscous solution at the tip end would be compelled to form joints because of the ionic balance among the unsolidified nanofibers, resulting in new nanowires after complete solidification. To further clarify the

Intertwining of Branching Jets

Based on a study on the fabrication of nylon-6 nanofiber/nets from polyelectrolyte solution, Tsou and coworkers proposed a plausible formation mechanism of intertwining of branching jets. According to their viewpoint, in addition to the main whipping jet, many tiny subsidiary jets form simultaneously and undergo the whipping process as well during electrospinning, as exhibited in Fig. 8.3. Owing to the vigorous whipping at high speed, the subsidiary jets would be intertwined in the chaotic whipping region when they overcame the obstacle of the mutual repulsive interaction. With the rapid solvent evaporation, the resultant networks consisting of subsidiary branching jets could be solidified between the scaffold nanofibers, resulting in the formation of 2D nanonets with interlinked nanowires. Although branching jets with microsized diameters in the straight jet segment have been observed by using a high-speed camera, the formation process of subsidiary jets cannot be observed, owing to their extremely small diameters and vigorous whipping. Therefore, this proposed mechanism based on the intertwining of branching jets is just a possible explanation, since it has not taken into account that

Intermolecular Hydrogen Bonding

By investigating the formation process and structures of nylon-6 (PA-6) and methoxypolyethylene glycol (MPEG) oligomer/nylon-6 nanofiber/net membranes, Kim et al. attributed the formation of nanonets to the hydrogen bonds between the nanonets and the nylon-6 nanofibers, and proposed the relevant intermolecular hydrogen bonding mechanism. Fig. 8.2 presents a schematic illustration of the hydrogen bond formation mechanism. In the high-voltage electric field, the electronegativity difference between hydrogen and oxygen/nitrogen atoms would be further enhanced and result in the high polarity of the molecules due to the more charges provided by the electric field. The protonated amide groups of ionic molecules would form strong hydrogen bonds with oxygen atoms of the nylon-6 molecules in scaffold nanofibers, and oxygen atoms of the nylon-6 molecules could connect with hydrogen atoms of the amide groups of the nanofiber as well, to form the interconnected spiderweb-like nanofibers/nets. Moreover, the intermolecular hydrogen bonding between oxygen and hydrogen atoms of MPEG molecules and amide groups of nylon-6 molecules was also proposed to reveal the formation of MPEG oligomer/nylon-6

Basic Setup For Electronetting

As electronetting and electrospinning are similar electrohydrodynamics techniques and the former accompanies the traditional electrospinning process, the basic setup for electronetting is almost the same as the electrospinning setup. The typical basic setup for electronetting includes two standard apparatuses of vertical and horizontal forms, of which the horizontal one is widely used, as shown in Fig. 8.1A. It is clearly shown that the typical electronetting setup consists of four parts, a high-voltage power supply, syringe pump, spin neret, and collecting receiver. The power supply with high voltage applied to the needle is used to induce the formation of charged liquids in the form of jets and/or droplets. A direct current power supply is usually employed for electronetting, while an alternating current supply can also be used as the spinning power. The spinneret with designed needle is attached to the syringe pump, which can control the flow rate of the precursor solution. Generally, the collecting receiver, such as a metal plate, screen, or rotating roller, is used to collect the nanofiber/net assemblies by virtue of the electric field between the needle of the spinneret and the receiver.

CENTRIFUGAL FORCE

Using PEO as a model polymer, Peterson et al. produced nanofibers at a production rate of 6.5 mg/h cm2(Fig. 7.19). Important parameters that affect the nanofiber production rate include voltage, spinneret rotation speed, solution feed rate, distance between spinning head and collector, and solution concentration. In this way, polyacrylonitrile fibers were produced successfully. This technique is also compatible with various collectors, such as a moving belt for collecting large membranes, parallel collector electrodes for aligned fibers, and parallel collector electrodes with one rotating electrode for producing short yarns.

A SUMMARY OF NEEDLE-LESS ELECTROSPINNING SPINNERETS

Moreover, asymmetrical spinnerets, such as a coil (Fig. 7.18), could also produce uniform nano- fibers and nanofiber mats. Unlike the symmetrical spinnerets, the coil spinneret shows an uneven electric field distribution.

Disk

A slowly rotating disk, which is partially immersed in polymer solution, eliminates the need for self replenishment of the solution at the fiber-spinning edge (Fig. 7.15). It also ensures a fresh coating of solution on the disk surface and prevents the solution from solidifying at the disk edge during electrospinning. Rotating cylinder and disk spinnerets have been analyzed by Niu et al. The rim radius of a cylinder spinneret can reduce discrepancies in electric field intensity and influence the fiber productivity. Thinner disk spinnerets increase the electric field intensity, leading to finer nanofibers and higher throughput.