| Electromagnetic radiation from various communication and electronic devices is a potential harm to human health.Reducing the harm of electromagnetic radiation to the human body remains a huge challenge due to the silent and permeable nature of electromagnetic waves through various non-conductive media.In recent decades,researchers from all over the world have devoted great efforts on addressing the issue of electromagnetic pollution.Among them,the development of flexible electromagnetic shielding(EM SE)materials is considered to be an effective strategy to protect human beings from electromagnetic radiation from electronic equipment.Existing EM SE composites often have shortcomings such as high cost,poor flexibility,inefficient EM SE performance,and poor biocompatibility,making it difficult to meet the higher requirements for more complex electromagnetic radiation pollution in the new era.Although the EM SE performance of graphene and other materials can exceed100 d B,it is still a challenge to achieve efficient EM SE performance and excellent flexibility to make them wearable.To address the shortcomings of existing EM SE materials,we have selected carbon nanotubes and graphene as conductive fillers,and PVDF as flexible matrix materials.Through a multi-layer design strategy optimized by simulation,we have prepared a series of flexible carbon-based EM SE composites for human electromagnetic protection.The main methods,research contents and research results are as follows:1.The differences between the three types of carbon nanotube(CNT)fillers with different conductivity and PVDF/CNT composites formed by polyvinylidene fluoride(PVDF)matrix were analyzed and compared through physicochemical characterization methods.The relationship between conductivity and EM SE performance was studied by combining experiments and COMSOL simulation.The results indicate that conductivity has a significant impact on the EM SE performance of the composite.The higher the conductivity of CNT,the better the EM SE performance of PVDF/CNT composite films.Subsequently,through theoretical simulation using COMSOL software,a flexible multi-layer polyvinylidene fluoride/carbon nanotube polyvinylidene fluoride(PVDF/CNT-PVDF)composite film was designed and prepared(sample numbering was carried out in the form of P/C-P-x-x * 0.1 and P/C-Px-0.3,where x represents the number of layers of the multilayer film and x * 0.1 and0.3 represent the thickness of the film in millimeters),and its EM SE and mechanical properties were studied.The theoretical and experimental results are in good agreement,and both indicate a positive correlation between the EM SE performance of the composite films with the thickness and number of layers,that is,the more layers,the better the EM SE performance.When the thickness remains unchanged at 0.3 mm,P/CP-6-0.3 has the best EM SE performance with an average of 43.9 d B.At this thickness,the mechanical tensile properties of the films first increase and then decrease with the increase of the number of layers.Among them,P/C-P-5-0.3 has the highest ultimate stress of 54.9 MPa,with a growth rate of 31% compared to single-layer films of the same thickness.In addition,the average EM SE of P/C-P-6-0.3 remained close to 100%after 1000 cycles of bending at 60 °,while the other layers of the films also approached100%.Compared to the trial and error research through a large number of experiments,the theoretical guidance strategy of this work may have certain advantages,which may provide useful guidance for designing high-performance wearable EM SE materials to protect humans from electromagnetic radiation damage.2.To further prepare flexible composite materials with higher EM SE performance,we selected graphene(GNP)with higher conductivity as the filler and prepared multilayer polyvinylidene fluoride/graphene polyvinylidene fluoride(PVDF/GNP PVDF)flexible composite films(similar to the naming of CNT based films,with sample numbering in the form of P/G-P-x-x * 0.1 and P/G-P-x-0.3).The structure and morphology of graphene and its composites were studied through physicochemical characterization,and the effects of layer number and thickness on the EM SE performance of thin films were studied theoretically and experimentally.The theoretical and experimental results are in good agreement,and both indicate a positive correlation between the EM SE performance of the composite film with the thickness and number of layers,that is,the more layers,the better the EM SE performance.When the thickness remains unchanged at 0.3 mm,P/G-P-6-0.3 has the best EM SE performance with an average of 69.7 d B.At this thickness,the mechanical tensile properties of the films first increase and then decrease with the increase of the number of layers.Among them,P/C-P-3-0.3 has the highest ultimate stress of 39.18 MPa,and its growth rate reaches 98.58% compared to single-layer films of the same thickness.In addition,after1000 cycles of bending for 60 °,the EM SE retention rate of P/C-P-6-0.3 is 98.85%,while the retention rate of other layers of thin films is also close to 100%.3.To investigate the feasibility of the composite materials prepared in this article in practical applications,we conducted experimental studies on the biocompatibility of the PVDF/CNT and PVDF/GNP composite films prepared.The results of LDH acute cytotoxicity experiment,cell attachment morphology staining observation experiment and CCK-8 cell proliferation experiment showed that after PVDF/CNT and PVDF/GNP composite film contacted with isolated somatic cell,the cell death rate caused by acute toxicity was about 11%,and then the cells attached and proliferated normally on the surface of the composite films,and the cytotoxicity of the film was relatively low.The skin irritation and animal sensitization experiment showed that both composite materials did not show significant erythema and edema in direct long-term contact with the skin,which can meet the requirements for human use of materials in contact with the skin. |
PDF Full Text Request