Electrospinning technology is an important method for preparing one-dimensional micro-nano materials developed in recent years. This method has many unique advantages: such as simple equipment, easy operation, fast and high efficiency, no pollution to the environment, etc.; continuous fiber bundles up to several meters can be prepared; the prepared non-woven micro-nano fibers have a large specific surface area , high porosity, excellent mechanical properties; because the method is carried out at normal temperature, the physical and chemical properties of each component can be well maintained. In the early stage of electrospinning technology research, researchers mainly focused on the preparation of polymer materials. Many polymers and biomolecules can be used to construct micro-nano structures with different structures, morphologies and functions through electrospinning technology. fiber. With the deepening of research, researchers began to use electrospinning technology to construct one-dimensional organic/inorganic nanocomposites. According to the application field of the prepared materials, suitable organic polymer materials can be selected to prepare organic/inorganic nanocomposite materials, and the polymer templates can also be removed by heat treatment to prepare inorganic nanomaterials. These novel and excellent composite materials can be widely used in electronics, optics, chemistry, biology, environment, energy, tissue as carriers for electronic devices, sensing materials, filter materials, reinforcement materials, superhydrophobic materials, catalysts and enzymes Engineering, biomedicine and catalysis and many other fields.
High-voltage electrospinning (electrospinning or electrostatic spinning), referred to as electrospinning, is a synthetic method of forming continuous fibers from polymer solutions or melts under the action of high-voltage electrostatics. In 1934, Formhals published a patent to describe the electrospinning equipment in detail for the first time, taking the process of obtaining polymer filaments by electrostatic repulsion between surface charges as an example, which is recognized as the beginning of the preparation of fibers by electrospinning technology. For a period of time after that, the development of electrospinning technology was relatively slow, and it was only recognized and used by a few people. Until the 1990s, the Reneker research group at the University of Akron in the United States carried out in-depth and extensive research on electrospinning technology and applications, and made great contributions to the promotion of electrospinning technology. Subsequently, the situation has changed dramatically, and numerous research groups in academia and industry have begun to work in related fields, and more than 100 different polymers have been electrospun into microfibers in solution or molten state. Now, electrospinning technology has become a widely recognized and mature technology for the preparation of ultra-long nanofibers, especially the application of this technology to the preparation of inorganic nanofibers has gradually attracted attention. This technique has shown great interest.
Electrospinning devices can generally be divided into 3 main parts (Figure 1): high-voltage electrostatic generator (high-voltage power supply), spinning tube (injection device) that can hold the polymer solution, and receiving device (metal plate and drum).
The working principle of electrospinning technology is: a high-voltage electrostatic field of several thousand to tens of thousands of volts is formed between the tip of the spinning tube and the receiver through a high-voltage power supply, so that a Taylor cone is formed at the spinning port. Under the action of the electric field force, after the solution in the spinning tube overcomes the surface tension, the Taylor cone is formed into a jet, which is further stretched during the jetting process, and gradually weakens with the action of the electric field force, reaching an unstable state. In the whipping zone, the solution is dispersed into countless finer fibers and finally coagulated on the receiving device in the form of non-woven fabrics to become micro-nano materials.
During the electrospinning process, the change of parameters can affect the morphology and structure of the prepared nanofibers, and the specific influencing factors mainly include three aspects.
① The characteristics of the precursor solution used in electrospinning include the viscosity, elasticity, conductivity, surface tension and relative content of the solute of the solution; for example, Fong et al. The viscosity is 1~20P, and the surface tension is between 35~55dynes/cm. When the viscosity is higher than 20P, the jet of the highly viscous solution is unstable and the electrospinning operation cannot be performed; when the viscosity is lower than 1P, the solution concentration is too low and the formation of droplets also makes the electrospinning operation impossible. Therefore, the viscosity of the solution has a particularly significant effect on electrospinning. Different polymers have different spinnable viscosity ranges due to their different properties. In fact, the viscosity of the solution is proportional to the amount of polymer, and the higher the polymer content, the higher the viscosity of the resulting precursor solution. The morphologies obtained by solution spinning with different viscosities are also different. For example, our related work investigated the spinning results of different viscosities of PMMA/N,N-dimethylformamide solutions. When the concentration of the solution is lower than 10%, the morphology obtained by electrospinning is a sphere, and when the concentration of the solution reaches 22%, the morphology obtained by electrospinning is a fiber. In addition, we also analyzed the effect of device variables on the electrospinning morphology. Under the condition of keeping other conditions unchanged, reducing the power supply voltage is not conducive to the electrospinning operation; while increasing the power supply voltage, the diameter distribution of the electrospun fibers is uneven and there are thicker ribbon fibers. It can be seen that the device variables of electrospinning are also an important factor affecting the final morphology.
②The variables of the electrospinning device include the size of the power supply voltage for electrospinning, the collection distance, and the advancing speed of the electrospinning solution; for example, Song et al. Keeping other conditions unchanged, when the voltage between the needle of the spinning tube and the receiving device is 5~15kV, and the distance is 10~25cm, the morphology of the sample changes from mutual adhesion to independent and uniform fibers. And they pointed out that changes in device variables had a larger effect on fiber structure than fiber diameter size.
③ The environmental factors in which the electrospinning device is located include temperature, humidity and air static electricity. For example, Demir et al. studied the effect of ambient temperature on electrospinning morphology. For electrospun polyurethane, the electrospun fibers obtained at 70 °C were more uniform than those obtained at room temperature. The main reason may be that temperature affects the solubility of the polymer, which in turn affects the final viscosity. In addition, Xia Younan also confirmed that proper humidity can make the structure of electrospun fibers smooth and uniform in diameter distribution.