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

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.

WIRE SPINNERETS

During the electrospinning process, the high voltage was applied to the stationary wires and a polymer solution was loaded on the surface of the wires by moving the wire through the polymer solution. Then, numerous jets were generated from the wire surface. It has a better spinning performance than the previous version, which use a rotating drum as spinneret.

CLEFT SPINNERET

Lukas et al. reported an electrospinning setup that used linear clefts as the spinneret (Fig. 7.6). The authors also developed a one-dimensional electrohydrodynamic theory to explain the process of electrospinning conductive liquids from an open plane surface (Fig. 7.6). During the electrospinning process, the amplitude of characteristic wavelength grew faster because of the electrical force. The fastest-growing stationary wave marked the onset of electrospinning from a free liquid surface. This theory not only predicated the critical value of the electrospinning process but also explained the upward needle-less electrospinning.

MAGNETIC FLUID

In 2004, Yarin and Zussman reported a needle-less electrospinning system that used a magnetic field to initiate the jet formation. The setup comprised a bottom layer of ferro magnetic fluid and an upper layer of polymer solution (Fig. 7.4A). When an external magnetic field was applied to the fluid system and an electric field was added simultaneously to the polymer solution layer, the ferromagnetic fluid triggered the formation of steady vertical spikes, which perturbed at the interlayer interface. Under the action of a strong electric field, these spikes were drawn into fine solution jets (Fig. 7.4B). Compared with multineedle electrospinning, this needle-less setup can produce polyethylene oxide (PEO) nanofibers with 12 times higher productivity. Nevertheless, the nanofibers electrospun are relatively coarser with larger diameter distribution.

Needle-less Electrospinning

Needle-less electrospinning appeared in the early 1970s, when Simm and coworkers filed a patent on using an annular electrode to electrostatically spin fibers for filtration appli cations. Next, Lukas et al. investigated the self-organization of charged jets initiated from the open free-liquid surface in the electrospinning process. Lin and colleagues developed a rotating spiral coil spinneret, which had a high fiber production rate with well-controlled fiber morphology. Liu et al. electrospun nanofibers by blowing air into the polymer solution. The bubbles generated assisted in jet initiation. Since 2008, growing research has been devoted to needle-less electrospinning. Research publications have been increasing constantly over the years. Over 100 articles about needle-less electrospinning or free-surface electrospinning have been published since 2007. The publication number between 2014 and 2016 was approximately 10 times more than that of 2007e2013 (Fig. 7.2A). Research is widespread in many countries. China, Australia, and the Czech Republic take about 80% of publications, followed by the United States, Germany, and England (Fig. 7.2B).

Multineedle Electrospinning Apparatus

Nanofiber yarn is defined as a twisted nanofiber bundle or tow featuring a morphology that is similar to filament yarn or spun yarn. Nanofiber yarn is mechanically suitable for weaving, knitting, and other methods used to produce fabrics. He and colleagues succeeded in producing continuous and twisted polyacrylonitrile nanofiber yarns by using a four-nozzle bubble electrospinning method, and the twist of the prepared nanofiber yarn could be adjusted by controlling the rotational speed of the collecting device, as shown in Fig. 6.13A and C. Two pairs of nozzles were positively and negatively charged, and the metal funnel collector was not grounded. After voltage was applied, the conjugate electric field came into being between the positive and the negative nozzles; however, the metal funnel located in the middle of the two groups of nozzles would have charges that were opposite those of the nearby charged nozzles. Therefore, induction fields were created between both edges of the funnel and their nearby charged nozzles. The electronic field lines were mainly distributed between the positive and the negative nozzles, and between the nozzles and the edge of the funnel. Because of the

Efficient Needle-free Electropinning Nanofiber Production Line MF01-003 ...

Qingzi Nano’s MF01 is an equipment of series of nanofiber production line, including needle spinning( MF01-001 and MF01-002) and needle-free spinning (MF01-003 and MF01-004) series. It is based on electrospinning technology to produce nanofiber membrane in high efficiency and quantity production, which can meet the growing need for nanofiber applications and achieve industrial benefits.

Features:

1. Quickly manufacture sample;
2. Automatic roll-to roll system;
3. Temperature and humidity controllable fabrication;
4. Nanofiber membrane drying system;
5. Safeguard system;

 Parameters:

1. Number of spinning electrode: 2;
2. Spinning electrode width: 600mm;
3. Effective width of nanofiber layer: 250-600mm;
4. Speed of roll-to-roll: 0-5m/min;
5. Feeding system: corrosion resistance, high-voltage resistance;
6. Power supply: 220V 50Hz.

Near Field Direct Writing Electrospinning Equipment M08 Spinning Process

Features: 

1. -Printing resolation less than 50nm;
2. -Nanofiber highly oriented and controllable;
3. - International R & D team pioneering technology;
4. - Exclusive patented technology;
5. -Micro nano manufacture excellent tools

Near Electrospinning Technology Classification

Solution Near-field Electrospinning

Solution near-field electrospinning process, the printing material is prepared into a solution, and using electrostatic field print orientation nanofibers. It can produce a fiber orientation controllable fiber diameter range is 50nm-20μm, the solution electrospun near-field have more suitable materials.

Melt near-field electrospinning

Melt Near-field electrospinning process, the printed material is heated and melted, assisted with the electrostatic field, fibers with a diameter range of 500nm-50μm can be prepared, high 3D printing capability, very suitable for producing three-dimensional biological tissue engineering scaffolds.

Near field electrospinning equipment parameters

1. High voltage power supply: 0-30kv, adjustable;
2. Solution spinning nozzle: solution supply volume at least 10μl/h;
3. Melt spinning nozzle: nozzle temperature: 0-300℃, adjustable, precision pneumatic extrusion;
4. Printing environment temperature: indoor temperature -50℃, adjustable;
5. Collection platform: printing range 150*150mm, platform speed: 0-200mm/s, resolution: 50nm;
6. Nozzle height: 0-80mm, adjustable, resolution: 50nm;
7. Printable materials: PE0, PVA, PLA, PCL, PLGA, chitosan, sodium alginate, collagen, hydroxyapatite, PVDF and other hundreds of organic or inorganic materials;
8. printable user-defined patterns;
9. printable 3D structure;
10. customizable : temperature controllable collector;
11. customizable : multi-nozzle device.

Single-bubble Electrospinning Unit

The structural diagram of a single-bubble electrospinning unit is shown in Fig. 6.7. Bubbles are formed on the mouth of the nozzle during the experimental process, and the forces on the charged bubbles are the electric field force (Fe), the force caused by the difference in air pressure inside and outside of the bubbles (Fp), and the surface tension of the bubbles (Ft) after voltage application. The bubble film composed of the spinning solution is drawn and then ruptured into multijets when the electric field force exceeds Fp and Ft. Finally, the multijets are stretched into nanofibers via the electric force. Bubbles can be continually formed on the mouth of the nozzle, and each bubble bursts to form high-speed multiple jets. The squirting speed of the air is controlled to increase nanofiber yield. The nanofiber yield is as high as 2.352 g/h, which is far greater than the yield achieved by conventional single-needle production.

Multi-needle Nanofiber Electrospinning Production Line MF01-001 Spinning...

Qingzi Nano’s MF01 is an equipment of series of nanofiber production line, including needle spinning( MF01-001 and MF01-002) and needle-free spinning (MF01-003 and MF01-004) series. It is based on electrospinning technology to produce nanofiber membrane in high efficiency and quantity production, which can meet the growing need for nanofiber applications and achieve industrial benefits.

Features:

1. Automatic roll-to roll system;
2. Precious feeding system;
3. Multi-needle electrospinning systems;
4. Temperature and humidity controllable;
5. Nanofiber membrane drying system;
6. Safeguard system;

Parameters:

1. Needle Qty: 256, or more( customizable);
2. Roller speed:0-20m/min, adjustable;
3. Feeding system: corrosion resistance, high-voltage resistance;
4. Continuous operation time:≥8 hours;
5. Power supply: 380V;
6. Effective width of nanofiber layer: 660mm, or other( customizable).

Maghemite (γ-Fe2O3) Fiber-in-tube And Tube-in-tube Nanostructures

Inspired by the nanowire-in-microtube structure, Jian-guo Guan and colleagues proposed a facile and effective nonequilibrium heat-treatment approach combined with electrospinning for fabrication of maghemite (γ-Fe2O3) fiber-in-tube and tube-in-tube nanostructures. The pre cursor was composed of PVP and iron citrate. Fig. 5.21 shows SEM images and corresponding TEM images of as-obtained γ-Fe2O3 fiber-in-tube and tube-in-tube fibers. The figure reveals that the tips of the inner structures are totally separated from the outer tube, and the inner and outer tubes have a closed end. The resultant γ-Fe2O3 fiber-in-tube and tube-in-tube nanostructures may have important applications in a number of fields, such as magnetic separable catalysts or catalyst-supporting mate rials, sensors, absorbents, microreactors, and so forth, because of their structural characteristics and good magnetic properties. This method can intentionally control the contraction direction of the precursor nanofibers during the heat-treatment process by adjusting only heating rate (R) of the calcination, as R can be easily utilized to tune the temperature gradient established in

Coaxial Cojetting Electrospinning Method

Because they have heterogeneous components and anisotropic properties, Janus fibers have wide applications in many fields. As a typical technique, side-by-side electrospinning has been proven to be a facile and cost effective method for preparing Janus fibers. But this method can be used only for fabricating dual-paratactic fibers. Based on this, Joerg Lahann et al. reported a coaxial cojetting electrospinning method with dual core flows and triple core flows. Using this method followed by crosslinking, microsectioning, and shell removal, Janus microcylinders and triple paratactic microcylinders composed of different polymers were prepared (Fig. 5.19A). Fig. 5.19B shows the cross-sectional CLSM images of triple coreeshell fibers. Blue, green, and red channels represent poly(vinyl cinnamate)(PVCi), PEO, and PMMA, respectively. Uniquely shaped building blocks can be fabricated by photopatterning of one hemisphere of the microcylinders. This approach can result in Janus coreeshell fibers and triple coreeshell fibers, where the core is defined by the parallel center jets. In all experiments, a PLGA solution was used as the shell stream, which governs the jetting performance and acts as a

Side-by-side Electrospinning Method

In 2015, White and Yu’s group further studied and developed the side-by-side electrospinning method by regulating the angle between the two needles of the spinneret. By varying the angle, the width, interfacial area, and volume of each side would also be changed. Therefore, different Janus nanofibers with adjustable structures were obtained. The diagram of the spinneret is shown in Fig. 5.17A, and the angle marked q could be tuned to change the morphology of the fibers. The solutions in this work were mainly PVP K-60/rhodamine B and Eudragit@L100/8-anilino-1-naphthalenesulfonic acid ammonium salt in a mixture of ethanol and DMAc. For the side-by-side electrospinning, the two solutions were stretched from their own needles with the same electrostatic charge and came together at the outlet of the nozzle. With their mutual electrostatic repulsion, the two solutions may separate from each other, which would lead to a failure to form the side-by-side structure. In this research, however, arranging the angle between the two ports to some suitable value would contribute to the fabrication of the side-by-side structure. The corresponding TEM images for when the values of the angle q were 40, 50,