Factors Affecting Electrospinning: Comparison
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Please note this is a comparison between Version 2 by Conner Chen and Version 1 by Sabarees Govindaraj.

Electrospinning can produce continuous nanofibers from a variety of materials. Processional, physical, systemic, and solution parameters, among others, impact the fiber morphology and properties of electrospun fibers.

 

  • electrospinning
  • nanofibers
  • phytoconstituents

1. Solution-Related Parameters

The solution’s parameters are crucial; it should have an ideal low surface tension and a sufficient charge density and viscosity to avoid the collapse of the jet into droplets before the solvent evaporates [30][1]. Polymer characteristics, including molecular weight, concentration, solution viscosity, surface tension, and solution conductivity, impact the shape and characteristics of nanofibers. Higher molecular weight produces viscous solutions compared to lower molecular weight because it indicates the length of the polymer chain, which determines the entanglements. During the process, these entanglements stop the jet from prematurely separating. A jet of a low-viscosity polymer solution fragments into tiny droplets or forms beaded threads. Viscous solutions promote chain entanglements and produce uniform fibers devoid of beads.
On the other hand, if the viscosity is too high, it will be challenging to pump the solution through the capillary, and it may dry up or drop at the tip. Surface tension reduces the solution’s surface area and drives it to condense into spherical droplets. When the concentration is low, solvent molecules with a high ratio have a stronger propensity to join and take the form of beads or spheres. Solvents with a low surface tension are needed to create bead-free, homogenous fibers. The jet’s electrostatic charge significantly increases when ions are present in the solution. For instance, increasing the jet stretching by a small amount of salt or polyelectrolyte in the electrospinning fluid might help generate smooth rather than beaded fibers [31][2].

2. Polymer Concentration

Droplets will form when the solution concentration is below the threshold value instead of fiber formation. High concentrations of a solution yield viscose solutions, which may pose processing problems. For instance, increased viscosity prevents the elongation and thinning of the jet and produces fibers with bigger diameters [25][3].

3. Processing Conditions

Electrospinning processing parameters include voltage, collector distance, flow rate, needle gauge, and collector type. High voltage provides the appropriate charges to the solution, which causes the jet to come out of the needle. With a relatively smaller Taylor cone, higher voltage accelerates a larger volume of electrospinning fluid [32][4]. The feed rate controls how much solution is present between the needle and the electrospinning target. Due to an increase in feed rate brought on by a voltage rise, the solution is stretched more and grows in diameter. Increased feed rate may also result in fiber fusing due to insufficient solvent evaporation before fiber collection. The reduction in distance causes a shorter flight time for the jet. So, the jet may not have enough time to solidify, resulting in the fusion of fibers. The diameter of the orifice also has an effect. Due to the jet’s shorter exposure to the environment, a smaller interior diameter lowers clogging. Reduced needle internal diameter causes a rise in the solution’s surface tension, which results in smaller droplets. The outcome was a decrease in the jet’s acceleration. As a result, before deposition, the jet is further stretched and elongated, resulting in fibers with a reduced diameter. The parameters above significantly impact the web characteristics and fiber shape in electrospinning. The collector’s design is another aspect. Regular electrospinning produces nanofibers that are randomly oriented. With a modification in collector design, it is possible to control the geometry of fiber deposition or get other desirable fiber patterns. One involves parallel bars with a space in the middle, resulting in aligned nanofibers.

4. Effect of Voltage

Raising the applied voltage would cause the polymer jet to discharge more forcefully, resulting in a rise in drawing tension [32][4]. The outcome is a reduction in fiber diameter, and as a result, the fiber diameter dispersion would rise, making process control more challenging. The ideal voltage is needed to start the polymer jet from the Taylor cone apex [33][5]. Before jet formation, the applied voltage had a major impact on the morphology of the droplets: faster electrospinning and enhanced solution flow rate produced by higher voltage [24][6].

5. Volumetric Flow Rate

The flow rate needs to be adjusted within the right range to stabilize the Taylor cone. Due to the slow flow rate in the needle, the Taylor cone frequently vanishes, and the electrospinning process momentarily stops. The vacuum created a faster flow which may cause the solution to accumulate at the tip of the needle. The rate of charge withdrawal into the solution depends on how long the ions are in contact with the needle because the surface charge density falls as the flow rate rises. The diameter, porosity, and shape of nanofibers are the characteristics influenced by the solution flow rate [24][6]. A constant and steady flow rate is required in electrospun materials to decrease bead formation. The diameter of electrospun nanofibers decreased by a slow flow rate. Additionally, compared to a quicker flow rate, a slow flow rate produced fewer beads and a smaller diameter [34,35,36][7][8][9].

6. Distance of Collector

It exhibits a negative power relationship as increasing the distance causes the polymer jet’s diameter to drop and the bending instabilities and whip action to lengthen. Surface charge density has a negative exponential connection. The surface charge density decreases as the gap distance increases. Fewer charged ions form as the distance between the charged solution and the collector grows [37][10]. Due to a reduction in the strength of the electric field between the two. The needle tip’s diameter, which has risen with increasing needle tip diameter, is another process parameter [33][5]. However, there is no correlation between needle diameter and subsequent fiber [32][4].

7. Effect of Conductivity

Compared to poor conductivity, high conductivity allows polymer solutions to transport more charge. As a result, increased conductivity produces stronger tensile pressures following the applied voltage and a decrease in nanofiber diameter [34,35,36][7][8][9].

8. Effect of Solvent

Before electrospinning, a solvent’s solubility and boiling point are crucial considerations. Due to the nanofibers’ quick evaporation and dehydration, volatile solvents are the best choice [38][11]. Substances having very low boiling temperatures that promote rapid evaporation should be avoided to prevent obstructing or restricting the needle orifice before electrospinning. On the other hand, high boiling point solvents may not fully dehydrate before striking the target, resulting in flat ribbon-shaped fibers rather than circular ones [39][12]. Researchers must give particular attention to assessing and selecting electrospinning solvents since the solvent’s volatility may alter the microscopic characteristics of electrospun fibers, such as porosity, shape, and size [40][13].

 

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