With the rapid development of electronic industry and the wide application of electronic equipment, electromagnetic wave radiation is considered to be the fourth public hazard after water pollution, noise pollution and air pollution.
The high-frequency electromagnetic waves emitted by electronic devices can not only cause the abnormal operation of electronic devices, but also affect people's normal life and even threaten the military secrets of the state. For example, high frequency electromagnetic radiation can affect or even destroy sensitive devices in military equipment, and make radio communication command system, modern weapon combat platform ineffective or out of control.
In addition, electromagnetic waves emitted by electronic devices may cause certain diseases, such as lack of sleep, dizziness and vomiting, which may lead to cancer, cardiovascular disease, etc.
As a result, the research and development of electromagnetic shielding/absorbing materials has been widely concerned in academic circles and industry circles around the world.
The so-called electromagnetic shielding/absorbing materials mainly include metal and polymer composites. Traditional metal - based electromagnetic shielding materials have high density, difficult structure design and so on.
Fortunately, polymer/absorbent composite materials have good design ability and can partially solve the technical bottleneck of metal based electromagnetic shielding materials. Among them, the polymer base electromagnetic shielding/absorbing material with micro-foaming structure is one of the hot research directions in this field in recent years.
The reason is that the pore structure not only gives the advantages of the light quality of electromagnetic shielding/absorbing materials, but also the bidirectional draft effect produced by the foaming process and the absorption agent in the secondary disperse polymer matrix. At the same time, the introduction of the bubble hole structure can cause the electromagnetic waves entering the material into the "labyrinth structure", thereby significantly improving the electromagnetic shielding effectiveness of the material and effectively preventing the electromagnetic leakage of the material.
Polymer resin itself has not, however, electromagnetic shielding/wave absorption performance, must be achieved by adding a lot of absorber, such as classes or carbon materials, and so on, but these are the absorbent and incompatibility polymer matrix, leading to an absorbent can't completely infiltration by the polymer substrate.
For foam polymer composite materials, a large number of absorber to add not only increase the number of defects in the matrix, and also enhance the stiffness of composite materials, which directly leads to a large amount of foaming agent cannot be used for the expansion of the material, therefore, highly filled polymer composites foaming becomes extremely difficult.
As a carbon material on the surface, graphene has good electromagnetic shielding/absorbing properties. In particular, the performance of graphene prepared by CVD and other methods is close to "perfect" and has no affinity with the polymer, and it is difficult to disperse evenly in the polymer matrix.
The author's research team, through the regulation of the graphite oxide contents of volatile matter, graphite oxide low-temperature atmospheric stripping is implemented, the preparation contains a lot of oxygen-containing groups of graphene oxide and successfully apply for the Chinese invention patent.
Polyimide micro-foaming electromagnetic shielding material is powerful.
Using graphene oxide surface oxygen groups, Chinese academy of sciences researchers in ningbo materials by blending method to improve the oxidation of graphene in thermoplastic polyimide resin dispersed, and successfully by the phase separation process in graphene oxide/polyimide composite materials uniform bubble pore structure is introduced.
The researchers found that the stretching effect of the polymer microfoaming process in situ contributes to the secondary dispersion of graphene and the orientation of graphene around the pore structure. The amount of oxide in the micro-foaming material can be as high as 10wt%, the density of the material is 0.3g/cm3, and the average ratio of the material in the x-band is 36.4dB/ (g/cm3).
However, the researchers also noted that the volume of the material increased during the polymer microfoaming process and the absorbent volume decreased. This directly damages the efficiency of polymer microfoaming electromagnetic shielding/absorbing materials.
To further solve the above problems, the researchers on the graphene surface in situ synthesized nano ferroferric oxide, electromagnetic matching using the composite nano-materials, the successful preparation of electromagnetic shielding performance of polyimide micro foaming more excellent electromagnetic shielding materials and electromagnetic shielding effectiveness than increased from 36.4 dB/(g/cm3) to 41.5 dB/(g/cm3).
More rare is that composite electromagnetic performance matching characteristics of nanometer materials to make polymer microcellular foaming material electromagnetic wave absorb more, rather than the reflection of electromagnetic wave, it reduces the electromagnetic waves again secondary pollution to the environment.
In the future, the size of the electronic products will be more and more small, electronics integration will be more and more high, this will inevitably require electronic shielding/absorbing material toward "quality light, thin thickness, wide frequency band, strong absorption" direction.
Using polymer microfoaming technology, the researchers of ningbo institute of Chinese academy of sciences have successfully developed the polymer functional micro-foaming film and the function microfoaming board material. The polymer matrix used can be high performance polyimide resin or flexible polyurethane thermoplastic elastomer resin. The materials developed can be used in several new material fields, such as radar penetration material, mobile phone electronic payment absorbing material, absorber patch, stealth structure functional integration material, etc.