Solution Electrospinning. Low surface tension solvents such as ethanol can be added to the electrospinning solution to aid in the formation of smooth nanofibers. Another way to reduce surface tension is to add a surfactant to the solution. More homogeneous fibers can be obtained by adding surfactant. Fiber morphology is improved even when a thin, insoluble surfactant is added to the solution
During electrospinning, the solution is stretched by repelling the charges on its surface. If the conductivity of the solution is increased, more charge can be transported to the electrospin beam. The conductivity of the solution can be increased by adding ions. Also, many drugs and proteins ionize when dissolved in water. If the solution is not completely drawn off, peeling will occur. Therefore, if a very small amount of salt or polyelectrode is added to the solution, the charges carried by the solution will increase and raise the voltage of the solution. As a result, smooth fibers are formed. Increasing the tensile strength of the solution makes it possible to obtain fibers with a smaller diameter. However, there are limits to reducing the fiber diameter. When the solution is stretched, a large viscoelastic force is generated against the force of the rod column.
Electrospinning fundamentals optimizing solution and apparatus parameters
As the conductivity of the solution increases with the presence of ions, the critical voltage required for electrospinning also decreases. Another effect of increased loading is greater instability of the whip. As a result, the degree of fiber accumulation increases. In this case, by increasing the beam path, smaller fibers are obtained.
The process parameters affecting the electrospinning process are the second most important group of parameters affecting the properties of the solution. Process parameters include applied voltage, solution feed rate, solution temperature, manifold type, nozzle diameter, and nozzle-to-manifold spacing.
Electrospinning of nanofibers from polymer solutions and melts
When a voltage is applied, the resulting electric field affects the drag and acceleration of the jet. When a higher voltage is applied, the solution has greater drag due to greater columnar forces in the jet. This not only reduces fiber diameter, but also causes the solvent to evaporate more quickly, resulting in drier fibers. When using low-viscosity solutions, the application of high voltage during electrospinning can lead to secondary jet formation. This reduces the diameter of the fiber. Another factor that can affect fiber diameter is the flight time of the electrospindle. The long flight time gives the fibers time to stretch and stretch before reaching the collector.
Acetic acid electrospinning solution
The feed rate determines the amount of solution available for electrospinning. There is some tension and feed rate to keep the Taylor cone stable. As the feed rate increases, the fiber diameter or bead size increases as the volume of solution drawn from the nozzle increases. However, there are limits to increasing the fiber diameter due to the high draw-in speed.
Solution electrospinning process
The temperature of the solution is effective to both increase the rate of evaporation and decrease the viscosity of the solution. At low viscosities, column forces create greater drag forces on the solution jet, resulting in smoother and finer fibers. By increasing the mobility of polymer molecules with increasing solution temperature, the attractive effect of the column forces on the solution jet also increases. Demir et al (2002), in their study on electrospinning PU nanofibers, found that the fibers obtained at high solution temperature are more uniform and homogeneous than the fibers obtained at room temperature.
They also indicated that the electrospinning process is faster at high solution temperatures, which could be beneficial for industrial applications. However, applying high temperatures to electrospinning solutions of biological materials such as enzymes and proteins can result in a loss of performance of these materials.
Both the shape and the material of the collector affect the electrospinning and the structure of the formed nanofibers. Many different collector designs, both movable and fixed, have been used in studies. The most commonly used collectors are aluminum plates. In addition, metal mesh, rotating drum, rotating disk, conveyor belt, triangular frame, parallel ring, and liquid bath are some of the materials used to collect electrospun nanofibers.