Green electromagnetic interference (EMI) shielding materials have been popularly accepted as the most promising EMI shielding material used in the electronic industrial community. Nevertheless, the design and optimization for both material and structure to achieve this function remain many challenges. Herein, Fe 3 O 4 @PA6 microspheres were fabricated by an unusual reaction-induced phase separation method, where Fe 3 O 4 nanoparticles were in situ introduced into the polymerization system. Interestingly, most Fe 3 O 4 nanoparticles spontaneously immigrated into PA6 microsphere, forming Fe 3 O 4 @PA6 composite microspheres, and more interestingly, the saturation magnetization and particle size of the microspheres are highly associated. Therefore, the microspheres with specific particle size and magnetic property were easily obtained by simple sieving. These microspheres were then coated by MWCNT and hot-compressed into EMI materials with segregated structures. A multilayered structure with positive conductivity gradients and negative magnetic gradients were created. Due to this structure, electromagnetic wave can enter the materials from the impedance matching channel without a large amount of reflection on the surface. The results show that with the increase in the number of composite layers, the EMI SE increases to 24.8 dB, and the R-value is significantly reduced to 0.51. This work provides a new feasible idea for designing low-reflection EMI composites.

The particle size and processability of the powder are the keys for successful nylon in selective laser sintering (SLS) 3D printing, but the nylon powders on the market have disadvantages such as uncontrollable particle size and large distribution, poor sphericity, and poor processability. In this study, graphene oxidehybridized polyamide 6 (PA6/GO) microspheres perfectly suitable for SLS 3D printing have been fabricated via reaction-induced phase separation. The selective distribution of GO in PA6 microspheres was characterized by thermogravimetric (TG) and transmission electron microscopy (TEM), and the particle size and morphology of PA6/GO microspheres could be effectively controlled by adjusting the ratio of caprolactam and polystyrene. Wherein, when the polystyrene addition amount is 15 wt%, the particle size of the PA6/GO microspheres is between 40 and 50 μm, and the sintering window and thermal stability of the microspheres are significantly improved. These experimental results are surprising for the preparation of new nylon SLS 3D printing materials.

No abstract

Isolation structure has been proven to be an effective method for constructing electromagnetic shielding composites, achieving high electrical conductivity with shallow filler content and high-efficiency electromagnetic shielding. However, there are still many challenges in further optimizing the design and improving absorption. This article designed a hybrid isolation structure using nylon magnetic microspheres and polystyrene (PS). First, we prepared PA magnetic microspheres (Ni@PA6M) with Ni nanoparticles uniformly dispersed by the reaction induced phase separation (RIPS) method, then mixed with MWCNT and PS at high speed and formed by hot pressing. Under the opti-

In this work, magnetic PA6 microspheres (PPA6@ NiM) with porous structures were prepared using the solvent coprecipitation method and electroless nickel plating technology, and the stacked magnetic microspheres were encapsulated with polydimethylsiloxane (PDMS) to obtain PPA6@NiM/PDMS composites. The existence of the porous structure increases the attenuation path of the electromagnetic wave, and the presence of the nickel layer improves the magnetic loss of the composite material to the electromagnetic wave and synergistically improves the absorption of the electromagnetic wave. Among them, the total shielding effectiveness (SET) of the PPA6@NiM4/PDMS composite is as high as 39.9 dB, and the reflection coefficient (R) is 0.83. To further increase the absorption effect of the composite material, an asymmetric gradient structure was constructed by utilizing the difference in electrical conductivity between the magnetic microspheres. The electromagnetic wave is incident from the surface with lower conductivity (impedance matching layer). It is reflected by the consistency with higher conductivity (strong reflective layer) than the bottom layer to increase the loss of electromagnetic waves inside the material. The composite SET constructed with M1 and M4 particles with the most significant difference in conductivity achieved 35.5 dB with an absorption coefficient (A) of 0.42. It shows that the porous combined asymmetric gradient structure we designed can effectively improve the shielding efficiency and absorption capacity of the composite material against electromagnetic microwaves and serve as a reference for creating high-absorbing and high-performance electromagnetic shielding materials.