| With the advancing progress in the field of science and speedy development of electronic information engineering,a series of electromagnetic radiation,interference and leakage caused by natural phenomena or man-made electronic equipment have become one of the urgent problems to be solved.Electromagnetic pollution not only affects the normal operation of peripheral instruments,but also seriously endangers human health.In order to reduce the pollution,the electromagnetic shielding materials that can effectively block the electromagnetic waves and reduce electromagnetic pollution gets more and more attention.In recent years,conductive polymer composites(CPCs)with corrosion resistance,low cost,low density and easy processing have replaced metal materials as one of the most popular shielding materials.At the same time,the controllable conductivity of CPCs provides the huge space for advancement of subsequent shielding materials.However,most polymers are electrically insulating and have poor electromagnetic interference shielding effectiveness except for a few conductive ones.Although the addition of conductive fillers can greatly improve the EMI shielding performance of CPCs,a large amount of conductive fillers need to be added to build dense shielding network to achieve the shielding effectiveness of 30 d B for commercial applications.Overmuch conductive fillers will reduce the mechanical properties of CPCs and increase costs.How to design the CPCs with efficient EMI shielding effectiveness under lower conductive fillers is a challenge in the field of electromagnetic interference shielding.In order to overcome the shortage of EMI shielding CPCs,the efficient electromagnetic shielding materials can be designed by controlling the distribution of fillers,in which the conductive network is enhanced to increase the reflection loss and absorption loss.On the other hand,multiple interfaces,which increases the loss paths of electromagnetic waves,are constructed to enhance the reflection/scattering of electromagnetic waves.Finally,the CPCs with excellent electromagnetic interference shielding effectiveness under the lower content of conductive fillers are designed.The main content are as follows:(1)Multi-walled carbon nanotubes(MWCNTs)were controllably distributed on the surface area of poly(?-caprolactone)(PCL)by the two-step melting compression.The macroscopic interfaces were introduced for enhancing the electromagnetic interference shielding effectiveness of the composites.The composites with sandwich structure had higher electromagnetic shielding effectiveness than the conventional PCLNT composites with randomly distributed MWCNTs with the same content of MWCNTs.In addition,the electromagnetic shielding effectiveness of the sandwiched composites depended on the thickness of conductive layer and the content of MWCNTs in the surface layer.The better shielding effectiveness were found in sandwiched composites with thicker conductive layers and higher MWCNTs surface layer.Furthermore,the different shielding effectiveness was obtained in the asymmetric sandwiched composites with different contents of MWCNTs on both sides when electromagnetic waves entered in it from different side.(2)A great deal of microscopic interfaces were constructed to improve the shielding effectiveness of the composites by enhancing the multiple reflection/scattering of electromagnetic waves.Specifically,the glass beads(?-GBs)were added to the PCL/MWCNTs(PCLNT)composites to construct the multi-interface for scattering electromagnetic waves.The shielding effectiveness of PCLNT/?-GB composites increased with the low content of ?-GBs,but decreased with the high content of ?-GBs,indicating the microwave attenuation of composites was dependent on the microwave absorption in the PCLNT conductive domain and the multiple scattering at the microscopic multi-interface.Furthermore,the absorption of microwaves can be promoted by increasing the conductivity(content of MWCNTs)in conductive domain,which compensated for the reduction of microwave attenuation ability caused by the decrease in the thickness of conductive domain.The shielding effectiveness of the PCLNT/?-GB composite with 50 wt% ?-GBs increased from ?34 d B to ?44 d B when the MWCNTs loadings in the PCL phase was increased from 3.0 wt% to 6.0 wt%.Therefore,the PCLNT/?-GB composites with high-performance microwave shielding performance can be realized by balancing the absorption in conductive domains between ?-GBs and the multiple scattering generated by the interfaces.(3)Furthermore,the reflection/scattering of electromagnetic waves was enhanced by increasing the interfacial conductivity,thereby improving the electromagnetic shielding performance of composites.Herein,the highly conductive interfaces were constructed based on the conventional segregated(CS)PLLA/PCLNT composites to prepare the interfacial-metallization segregated(IMS)composites.The shielding performance of IMS composites was generally higher than CS composites with the same MWCNTs loadings.For instance,the IMS composites with only 0.44 vol% Ag NPs achieved an excellent shielding effectiveness of 43.3 d B,which exceeds the CS composites(32.1 d B)about 35%.In addition,the shielding performance of the IMS composites dropped sharply after breaking the segregated structure.Therefore,the highefficiency microwave attenuation capability of IMS composites mainly depended on the microscopic multi-interface structure of the segregated structure and the high conductivity of interfaces,which provided a new idea for designing the CPCs with efficient electromagnetic shielding effectiveness under the lower content of conductive fillers. |
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