Anti-static mat
Anti-static mat (floor mat) is mainly made of conductive materials, static dissipative materials and synthetic rubber. Made. The product is generally a two-layer structure, the surface layer is a static dissipative layer, and the bottom layer is a conductive layer. The mat has a long-lasting use, has good acid, alkali and chemical resistance, and is wear resistant and easy to clean.
Any two materials with different chemical compositions, or two materials with the same chemical composition but different physical states, have different charge carrier energy distributions in their internal structures. When such two materials are in contact and rubbed, charge redistribution occurs on the surface of the antistatic mat to form an electric double layer. When they are re-separated, each material will have a positive (or negative) charge that is excessive compared to contact and friction. This process of charging an object is called electrification.
The electrification process generally has contact electrification, triboelectric electrification, photovoltaic electrification, thermoelectric emission electrification, field emission electrification, dispersed particle electrification, mechanical fracture electrification, and corona electrification. The most common are contact electrification and triboelectric charging. The electrification characteristics of light friction can be approximated as a series of close contact and separation processes, causing charge to transfer between the surfaces of the antistatic clothing to generate static electricity. However, in the case of severe friction, due to the relative movement of the local contact surface of the antistatic shoe at a relatively high speed, the antistatic shoe may be heated or even softened, and there may be mass exchange between the two friction surfaces. Therefore, the symbol of the anti-static pad material frictional electrification sometimes relates to the pressure on the contact surface of the anti-static clothing. For example, when the viscose silk fabric is rubbed with the stainless steel rod, the fabric is positively charged when the pressure is low, and negatively charged when the pressure is high. . Another example is when two rubber rods of the same material are used for one-and-one static friction, and the moving rod is positively charged. After repeated intense friction, the original positively charged rod becomes negatively charged. In addition to the high contact potential of the two objects, these phenomena should also consider the Seebeck effect (ie, the temperature difference electromotive force effect). Friction causes local heating, which causes carriers to transfer from high temperature to low temperature. Friction causes mechanical breakdown and thermal decomposition of macromolecules to generate electrons or ions, as well as piezoelectric and thermoelectric effects. So intense friction is a complex electrification process.
The static electricity of the polymer should be studied in combination with the conductive mechanism. When the metal is in contact with and separated from the antistatic clothing or the polymer, the electrification may occur due to electron transfer or ion transfer, but most of the electron transfer may be accompanied by a certain amount of ion transfer to cause electrification.
The electron transfer depends on the Fermi energy or Fermi level (E) of the contact object, and its value is equal to the electrochemical potential of the electrons in the solid, so E is a thermodynamic function. The electrons entering the solid can be regarded as ending at E, and the escape of electrons from the solid can be regarded as starting from Er on average. When the electron transfer is balanced, the Fermi level of the whole system should be equal in the energy level diagram. The work function or electron work function is the free electron energy E. The difference with E. When two objects are in contact, the direction of electron flow depends on the level of the Fermi level or the work function value before the contact, and the electron always flows from one side (E, low) in which the work function is small (E, high). As a result of the electron movement, an electrostatic potential is generated. When the difference between the work function between e and the two objects is equal, the balance is reached. At this time, each object has a positive or negative equivalent charge near the relative interface, but is measured from the outside. Not charged. As the two objects separate, they begin to form positive and negative charges, respectively. In the separation process, the actual observation after separation is caused by tunneling, field emission, gas discharge, and charge diffusion through the surface and inside of the object. The total static charge reached is less than the total charge at the time of contact. At the time of separation, the potential difference between the two objects is rapidly increased due to the greatly reduced capacitance, thereby generating a relatively high electrostatic voltage. The result of contact electrification is always negative with a large work function and a positive power with a small work function. The triboelectric charge sequence of the polymer is substantially identical to the order of its work function size.
People have long tried to use anti-static mats to explain the role of polar groups in the electrostatic charging of anti-static shoes. If the antistatic mat has a higher polarity level than the main chain level. Then the electrification of such an antistatic suit must depend on the structure of the polar group. In recent years, great progress has been made in the application of quantum theory to antistatic shoes, such as Andre and Del}lall. The ab initio calculation method and some semi-empirical formulas have been used to calculate the energy band structure and density of states of simple polymers. Verbist used x-ray photoelectron spectroscopy theory and method to determine the electronic structure of the polymer and used it to test the theoretical results of the band. Collins uses Gree. ’. The functional method explores the excited state problem in solids and polymers. Brandow established the relevant energy expressions for the closed-shell and open-shell systems, and derived the effective 7r electron Hamiltonian operators, etc., which are very useful in the theory of polymer electronic structure. However, in the relationship between the electronic structure of the polymer and the electrostatic charging, there are still many theoretical and experimental problems that have not been solved, and further research is needed in the future.
