Application progress of the hottest low temperatur

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Application progress of low-temperature plasma technology in surface modification

[Key words] low temperature, plasma, surface modification

[Abstract] this paper introduces the properties, characteristics and surface modification principle of low-temperature plasma technology, and summarizes the application progress of low-temperature plasma technology in surface modification while reaching all the required mechanical properties from three aspects of surface treatment, surface polymerization and surface grafting

the energy of particles in low-temperature plasma is generally about several to dozens of electron volts, which is larger than the binding bond energy of polymer materials (several to dozens of electron volts), and it can completely break the chemical bonds of organic macromolecules and form new bonds; However, it is far lower than high-energy radioactive rays, which only involves the surface of the material and does not affect the properties of the matrix [1 ~ 3]. In the low-temperature plasma in the non thermodynamic equilibrium state, the electrons have high energy, which can break the chemical bonds of molecules on the surface of materials, improve the chemical reaction activity of particles (greater than that of thermal plasma), and the temperature of neutral particles is close to room temperature. These advantages provide suitable conditions for the surface modification of heat sensitive polymers

1 forming device and influencing factors

plasma with different properties and application characteristics can be obtained by selecting appropriate discharge mode. Generally, hot plasma is produced by corona discharge of gas at atmospheric pressure, and cold plasma is formed by glow discharge of low-pressure gas

the thermal plasma device [4] uses the tip of the charged body (such as knife or needle tip and slit electrode) to create an uneven electric field, which is called corona discharge. The use voltage and frequency, electrode spacing, treatment temperature and time have an impact on the corona treatment effect. With the increase of voltage and power frequency, the treatment intensity is high and the treatment effect is good. However, too high power frequency or too wide electrode gap will cause too many ion collisions between electrodes, resulting in unnecessary energy loss; If the electrode spacing is too small, there will be induction loss and energy loss. When the treatment temperature is higher, the surface characteristics change faster. With the extension of treatment time, polar groups will increase; However, if the time is too long, decomposition products may be produced on the surface, forming a new weak interface layer

cold plasma device [5] is to set two electrodes in a sealed container to form an electric field, and use a vacuum pump to achieve a certain degree of vacuum. As the gas becomes thinner and thinner, the molecular spacing and the free movement distance of molecules or ions become longer and longer. Under the action of an electric field, they collide to form a plasma, which will emit glow at this time, so it is called glow discharge treatment. The pressure of glow discharge has a great influence on the material treatment effect, and it is also related to discharge power, gas composition and flow velocity, material type and other factors

various low-temperature plasma processing equipment can be formed by the combination of different discharge modes, working material states and the above factors affecting plasma generation

2 application in surface modification

low temperature plasma technology has the advantages of simple process, convenient operation, fast processing speed, good treatment effect, small environmental pollution, energy saving and so on. It is widely used in surface modification

2.1 surface treatment

through low-temperature plasma surface treatment, the material surface has a variety of physical and chemical changes, or produces etching and roughness, or forms a dense cross-linking layer, or introduces oxygen-containing polar groups, so that the hydrophilicity, adhesion, dyeability, biocompatibility and electrical properties are improved respectively

the surface of silicone rubber was treated with several commonly used plasmas. The results showed that N2, AR, O2, ch4-o2 and ar-ch4-o2 plasmas could improve the hydrophilicity of silicone rubber, among which ch4-o2 and ar-ch4-o2 had better effects, and did not deteriorate with time [6]. Parker pen company in the UK used plasma technology in the modification process of plastic components to control ink flow, which improved the wettability of plastic

literature [7 ~ 9] shows that when PE, PP, PVF2, LDPE and other materials are treated with low-temperature plasma under appropriate process conditions, the surface morphology of the materials changes significantly, and a variety of oxygen-containing groups are introduced, so that the surface changes from non-polar and difficult viscosity to a certain polarity, easy viscosity and hydrophilicity, which is conducive to bonding, coating and printing

plasticizers, initiators, residual monomers, degradants and other low molecular substances added to polymer materials such as plastics, rubber and fibers in the forming process are easy to precipitate and converge on the surface of the material to form an amorphous layer, which makes the wettability and other properties worse. Especially for medical materials, the exudation of low molecular weight substances will affect the normal function of biological bodies. Low temperature plasma technology can form a cross-linking layer on the surface of polymer materials and become a barrier for the exudation of low molecular substances

Li Ying et al. [10] modified PI, pet and PP films with different plasma, and found that the surface resistance of the treated films decreased by 2-4 orders of magnitude, and the dielectric loss and dielectric constant of the materials also changed. Applying this technology to the field of microelectronics technology can greatly reduce the size of the connecting circuit of electronic components and significantly improve the reliability of operation

2.2 surface polymerization

most organic gases polymerize and deposit on the solid surface under the action of low-temperature plasma to form a continuous, uniform, pinhole free ultra thin film, which can be used as protective layer, insulating layer, gas and liquid separation film and laser photoconductive film of materials, and can be used in many fields such as optics, electronics, medicine and so on

an optical lens can be made of polymethyl methacrylate or polycarbonate plastic, which is cheap and easy to process, but its surface hardness is too low, which is easy to produce scratches. The scratch resistance and reflection index can be improved by depositing a thin layer of 10nm on the surface of the lens with organic fluorine or silicone monomers and low-temperature plasma polymerization technology [6]. There are also reports abroad that plasma chemical vapor deposition technology has been applied to glass for plastic windows, automotive shutters, and reflectors for neon and halogen lamps

plasma polymerized film has many properties, which can make the same substrate used in many fields. Coating diamond-like carbon on metals and plastics. The experimental data measured by fatigue experiments are generally very dispersed. The chemical vapor deposition technology of coating is to introduce carbon containing gas into the plasma. The coating is chemical resistant, pinhole free, impermeable, and can prevent various chemicals from eroding the substrate. Similarly, the antifriction coating can be applied to the windshield wiper for 1 price and 1 goods, or the low friction coating can be applied to the computer disk to reduce the magnetic impact of the magnetic head

after plasma polyethylene film was deposited on the surface of silicone rubber, the permeability coefficient of silicone rubber to oxygen decreased significantly. The reverse osmosis membrane prepared from nitrogen-containing monomers can block up to 98% of salt. In vivo sustained-release drugs generally use polymer microcapsules, and plasma can also be used to install the experimental body polymerization technology to form a reverse osmosis film on the surface of microcapsules. The application study of plasma polymer film on sensing elements shows that factors such as discharge power have a great influence on the film resistance. The hydrophobicity and dyeing properties of fabrics treated with various vinyl monomers and AR glow discharge can be improved in a very short time

2.3 surface grafting

the surface of materials is modified by plasma graft polymerization, and the graft layer is covalently bonded with surface molecules, which can obtain excellent and durable modification effects. In the United States, polyester fiber was treated by glow discharge plasma and grafted with acrylic acid. After modification, the water absorption of the fiber was greatly improved, and the antistatic property was also improved. Bai Mindong et al. [5] treated the surface of nylon silk with Ar plasma, introduced acrylic acid, and grafted polymerization to enhance the antistatic property of nylon silk. Low temperature plasma grafting modification of wool fabric raw materials and finished products can improve the surface properties of plush, enhance coloring, soften the fabric, reduce shrinkage, and the wool fabric body is not affected [11]. Polyester fiber is strong and durable, but its structure is tight, water absorption is poor, and it is difficult to dye. Wang Xueyan [12] et al. Grafted polyester fabric with acrylamide initiated by low-temperature nitrogen plasma. After grafting, the dye uptake, dyeing depth, and hydrophilicity of polyester fabric are significantly improved

the surface treatment of medical materials by low-temperature plasma can introduce amino, carbonyl and other groups, and the grafting reaction of bioactive substances with these groups can be fixed on the surface of materials. Polypropylene membrane was treated with plasma, amino group was introduced, and then covalently grafted to fix glucose oxidase. After determination, the grafting rates were 52% respectively μ G/cm2 and 34 μ g/cm2。


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