Efficient Electromagnetic Wave Absorption and Thermal Infrared Stealth in PVTMS@MWCNT Nano‑Aerogel via Abundant Nano‑Sized Cavities and Attenuation Interfaces

Pre-polymerized vinyl trimethoxy silane(PVTMS)@MWCNT nano-aerogel system was constructed via radical polymerization,sol-gel transition and supercritical CO_(2)drying.The fabricated organic-inorganic hybrid PVTMS@MWCNT aerogel structure shows nano-pore size(30-40 nm),high specific surface area(559 m^(2)g^(−1)),high void fraction(91.7%)and enhanced mechanical property:(1)the nano-pore size is beneficial for efficiently blocking thermal conduction and thermal convection via Knudsen effect(beneficial for infrared(IR)stealth);(2)the heterogeneous interface was beneficial for IR reflection(beneficial for IR stealth)and MWCNT polarization loss(beneficial for electromagnetic wave(EMW)attenuation);(3)the high void fraction was beneficial for enhancing thermal insulation(beneficial for IR stealth)and EMW impedance match(beneficial for EMW attenuation).Guided by the above theoretical design strategy,PVTMS@MWCNT nano-aerogel shows superior EMW absorption property(cover all Ku-band)and thermal IR stealth property(ΔT reached 60.7℃).Followed by a facial combination of the above nano-aerogel with graphene film of high electrical conductivity,an extremely high electromagnetic interference shielding material(66.5 dB,2.06 mm thickness)with superior absorption performance of an average absorption-to-reflection(A/R)coefficient ratio of 25.4 and a low reflection bandwidth of 4.1 GHz(A/R ratio more than 10)was experimentally obtained in this work.

PP／PDMS共混物的连续挤出发泡成型

用二氧化碳作为发泡剂,利用串联发泡挤出系统研究了聚丙烯(PP)/聚二甲基硅氧烷(PDMS)混合物的膨胀比及泡孔密度,同时用马来酸酐接枝PP(PP-g-MAH)作为增容剂来提高PDMS与PP的相容性。结果表明,混合物的最大膨胀比可达25倍,而纯PP的最大膨胀比只有8倍。另外,与纯PP相比,混合物的泡孔密度显著提高(尤其是在低发泡剂浓度时)。

聚乙烯醇/微纤化纤维素复合微发泡材料的制备

通过溶液浇铸法制备了聚乙烯醇(PVOH)/微纤化纤维素(MFC)复合薄膜材料,以超临界二氧化碳(scCO2)为物理发泡剂,采用间歇式降压法制备了一系列PVOH/MFC复合微发泡材料,主要讨论了在没有水分的影响下,不同发泡温度和时间以及MFC含量对PVOH/MFC复合微发泡材料的泡孔形貌、泡孔尺寸和泡孔密度的影响;同时,也对MFC的分散性和PVOH/MFC复合材料的流变性能和热性能对发泡行为的影响进行了研究。实验结果表明,均匀分散在PVOH基体中的MFC作为异相成核剂提高了气孔成核能力,且随着MFC含量的增加,泡孔尺寸降低,泡孔密度增大;并研究了发泡温度对PVOH/MFC复合材料的发泡形貌的影响,获得最优发泡温度。

Layered Foam/Film Polymer Nanocomposites with Highly Efficient EMI Shielding Properties and Ultralow Reflection

Lightweight,high-efficiency and low reflection electromagnetic interference(EMI)shielding polymer composites are greatly desired for addressing the challenge of ever-increasing electromagnetic pollution.Lightweight layered foam/film PVDF nanocomposites with efficient EMI shielding effectiveness and ultralow reflection power were fabricated by physical foaming.The unique layered foam/film structure was composed of PVDF/SiCnw/MXene(Ti_(3)C_(2)Tx)composite foam as absorption layer and highly conductive PVDF/MWCNT/GnPs composite film as a reflection layer.The foam layer with numerous heterogeneous interfaces developed between the SiC nanowires(SiCnw)and 2D MXene nanosheets imparted superior EM wave attenuation capability.Furthermore,the microcellular structure effectively tuned the impedance matching and prolonged the wave propagating path by internal scattering and multiple reflections.Meanwhile,the highly conductive PVDF/MWCNT/GnPs composite(~220 S m^(−1))exhibited superior reflectivity(R)of 0.95.The tailored structure in the layered foam/film PVDF nanocomposite exhibited an EMI SE of 32.6 dB and a low reflection bandwidth of 4 GHz(R<0.1)over the Kuband(12.4-18.0 GHz)at a thickness of 1.95 mm.A peak SER of 3.1×10^(-4) dB was obtained which corresponds to only 0.0022% reflection efficiency.In consequence,this study introduces a feasible approach to develop lightweight,high-efficiency EMI shielding materials with ultralow reflection for emerging applications.

乙烯-乙烯醇共聚物/碳纳米管复合发泡材料的电磁屏蔽性能研究

选用高机械强度和耐气候性乙烯-乙烯醇共聚物(EVOH)作为基体,添加高效导电填料多壁碳纳米管(MWCNTs),同时为了进一步提高材料性能,添加了聚醚多元醇(EOPO)与4,4'-二苯基甲烷二异氰酸(MDI)的共聚物.采用绿色环保的超临界二氧化碳发泡法制备EVOH/MDI-g-EOPO/MWCNTs纳米复合发泡材料,结果表明在EVOH/MDI-g-EOPO/MWCNTs复合材料中引入多孔结构,利用多层界面反射-吸收电磁波,比电磁屏蔽性能提升270%.通过调控MWCNTs体积含量与泡孔结构,当MWCNTs体积含量达到2.7 wt%时,EVOH/MDI-g-EOPO/MWCNTs复合发泡材料在X波段(9~12 GHz)表现出优异的比电磁屏蔽效能(41.76 dB·cm^(3)/g).

Microcellular foamed polyamide 6/carbon nanotube composites withsuperior electromagnetic wave absorption

Electromagnetic (EM) wave pollution causing damage to precision equipment and threatening thehealth of living organisms has attracted considerable attention. Herein, promising microcellular foamedpolyamide 6 (PA6)/carbon nanotube (CNT) composites for highly efficient EM wave absorption were successfully fabricated using supercritical CO_(2) foaming. Nanocomposites foams with a void fraction rangingfrom 38.7% to 85.1% were achieved, providing a platform to assess the correlation of the electrical conductivity, the dielectric permittivity and the EM wave absorption properties with porosity. Notably, theFoam-257.5C sample with a void fraction of 38.7% exhibited outstanding EM wave absorption characteristics at a thickness of only 1.59 mm and an ultra-low reflection loss value of -55.3 dB (99.9997% wave absorption). Most importantly, the effective absorption bandwidth (EAB) of the Foam-257.5C sample couldcover the entire Ku band (12.4–18 GHz) by slightly adjusting the thickness from 1.20 to 1.60 mm. Thesuperior EM wave absorption performance of the Foam-257.5C sample was attributed to multiple reflections and scattering at the solid-gas interfaces, favorable impedance matching due to the existence ofa large polymer-air interface area, conductive loss near the interfaces and interfacial polarization. Thus,this study offers an eco-friendly, simple and versatile methodology to develop high-efficiency, flexiblepolymer-based EM wave absorbents.

Recent progress and perspective in additive manufacturing of EMI shielding functional polymer nanocomposites

Because of rapid progress in the electronics industry,the market has faced a huge demand for novel materials in the field of electromagnetic interference(EMI)shielding.Conductive functional polymer composites have demonstrated great potential to fulfill this requirement.To synthesize the polymeric composites,functional conductive nanoadditives such as graphene,carbon nanotubes,and MXene are commonly added to polymeric matrices,and the conductive polymer nanocomposites exhibit promising electrical conductivity as well as EMI shielding performance.Additive manufacturing(AM),also referred to as threedimensional(3D)printing,has been increasingly employed to fabricate complicated geometry components in the medical,aerospace,and automotive industries.AM has also been used to fabricate advanced EMI shielding materials for sensors,supercapacitors,energy storage devices,and flexible electronics.This review aims at introducing the different 3D printing methods applied for the fabrication of EMI shielding polymer nanocomposites.The impact of the AM process on the functionality of the samples is also reviewed.Additionally,the influence of the nanofiller type and amount on the microstructure and performance of the fabricated nanocomposites is discussed.Finally,the prospects and recommended works for future study are outlined.

Tailoring surface features and pore structure by carbon spiral fibers to construct the high-strength carbon foams for the fast and cyclic photo-thermal oil absorption

Two key limitations affecting the commercial application of carbon foams for fast clean-up of varied oils are the complex synthesis process and poor mechanical stability.In this work,an effective method is reported to fabricate the efficient oil-absorbing materials(CSF@MCF)of carbon spiral fibers(CSFs)anchored on melamine carbon foam(MCF)with superior mechanical properties and excellent photothermal con-version.The interwoven CSFs can not only provide extra rigidity but also reduce the stress concentration of the carbon skeleton,which greatly improves the mechanical properties with 6.3 times maximum compression stress and 4.5 times ultimate tensile strength than MCF.In addition,the pure carbon component can reduce the interface resistance and excite the free electrons more easily,thus realizing high-efficiency photothermal conversion in a wide range of wavelengths.Under light irradiation,the CSF@MCF can be quickly heated up to 70℃and achieve ultra-high absorption of crude oil,up to 62 g g_(-1),due to its low density and large absorption volume.Meanwhile,the CSF@MCF exhibits impressive absorption stability with persistent superhydrophobicity and a high recovery efficiency of over 85%.Superadding its simple preparation process,low production cost,and excellent acid-alkali resistance,the CSF@MCF shows great commercial potential for effectively absorbing varied oils.