随着电子行业的迅猛发展,尤其是5G高频通信技术、智能穿戴设备、自动驾驶技术的全面铺开,电子通信设备不断朝着小型化、多功能化、高功率化发展[1-2]。这些设备在提供便利的同时,也带来了日益密集的电磁波辐射,不仅对电子设备的正常运行造成干扰,还可能对人体健康造成一定程度的替在危害,长时间暴露于电磁辐射环境中,可能会引发人体内脏器官功能失调,表现为头痛、失眠、疲劳以及记忆力减退等临床症状[3-4]。鉴于此,研制具有卓越抗电磁干扰(EMI)性能的屏蔽材料对于保障人体健康以及维护精密仪器设备运行具有极其重要的意义。传统的金属屏蔽材料导电性能优异,屏蔽效果好,但其密度较高,不利于轻量化设备的使用。此外,金属材料在潮湿或酸碱环境中易发生腐蚀导致屏蔽性能降低和使用寿命减少[5],因此研究者们急需开发轻质、稳定、柔性好,兼具优异电磁屏蔽性能的屏蔽材料[6-7]。纳米材料如石墨烯纳米片、碳纳米管、磁性四氧化三铁等在制备电磁屏蔽材料方面具有此类优势[8],但其比表面积大易团聚,导致其宏观材料的力学性能及屏蔽性能的下降,因此开发功能一体化的聚合物基复合材料是理想的电磁屏蔽材料。
纤维素,是一种广泛存在于植物细胞壁的天然高分子材料,是地球上储量最为充足的资源之一,具备可再生性和生物降解性,材料来源绿色丰富。纤维素纳米纤维[9-10](CNFs)是一种具有纳米尺度的纤维素材料,其密度低、柔韧性好、强度高,能够满足对重量敏感、柔性要求高的电磁屏蔽应用场景的需求,如航空航天、可穿戴设备等[11-12]。CNFs表面富含羟基,这些羟基使得CNFs具有较高的反应活性,易于通过酯化、醚化、接枝共聚等化学方法进行改性。良好的界面相容性使其能够与多种纳米功能组分实现有效复合,且可以通过真空辅助自组装[13-14]、冷冻干燥[15-16]、化学镀[17-18]等方法制备机械强度优异的薄膜、多孔材料等复合材料。此外,CNFs独特的纳米级纤维结构和高长径比为其在复合材料中的应用提供了优势。CNFs纳米级纤维结构能够提供大量的接触点和界面,有利于与其它纳米材料复合,从而构建起高效的导电网络[19]。同时,高长径比使得CNFs在复合材料中能够形成连续的路径,有效传导热量,构建热传导通路[20],因此,CNFs能够在复合材料中实现电磁屏蔽与热管理的双重功能,进而达成多功能化,拓展其在不同领域的应用。
1 电磁屏蔽原理
电磁干扰屏蔽(EMI shielding)是指通过屏蔽体将电磁波发射源限定在特定区域内,或阻止外部电磁干扰波进入受保护区域,以保障电子装置、系统组件或特定空间在预设电磁条件下能够稳定运行。目前,关于电磁干扰的屏蔽作用机制存在多种理论模型,主要包括传输线理论、涡流效应理论和全波电磁场理论等[23]。这些理论具有不同的适用场景,其中涡流效应理论在低于1 MHz频段会出现趋肤深度估算误差,全波电磁场理论计算复杂度过高,难以指导工程实践。传输线理论因其精度高、模块化设计优势,被广泛应用于复合材料屏蔽结构设计。Schelkunoff通过将屏蔽体等效为具有特定阻抗特性的传输线,提出电磁波能量损耗主要包括反射损耗、吸收损耗、多重反射损耗[24-25]。当电磁波到达屏蔽体表面时,若屏蔽材料与周围介质在电磁参数上存在明显差异(主要表现为阻抗失配),则产生电磁波反射效应,形成界面反射损耗。若材料与介质的阻抗接近,则电磁波透过屏蔽材料表层继续传播,材料内部结构与成分能够通过特定的物理过程,如介电损耗和磁损耗耗散电磁波的能量,称为吸收损耗[26]。在屏蔽材料内部若存在多孔结构、多层结构等复杂结构,电磁波会在内部产生多重反射损耗[27]。未被损耗的剩余能量最终会透射过屏蔽材料。
2 纤维素基电磁屏蔽膜材料
2.1 单层结构膜材料
Shao等[35]通过真空辅助过滤法构建了纤维素纳米纤维/生物基阻燃剂/石墨烯纳米片(CNFs/AAZ/GNPs)复合薄膜,利用GNPs的高导电性形成连续导电网络,使薄膜在20 % GNPs含量下实现2 079.2 S/m的电导率和37 dB的屏蔽效能。受限于二维片层结构的单一损耗机制,薄膜的吸收损耗占比仅为56%,表明阻抗匹配有待优化。此外,GNPs与CNFs基体之间的界面相容性较差,尤其是在GNPs含量较高时,会降低薄膜的柔韧性和拉伸强度。
Liu等[36]采用木质纤维素纳米纤维与MXene进行混合,通过热压工艺将厚度压缩至33 μm,构建了具有高度取向结构的复合薄膜。致密化处理使纤维素纳米纤维与MXene片层紧密堆叠,形成“砖-泥”结构,显著提升薄膜的力学性能,拉伸强度可达235.28 MPa。该结构通过多重反射和界面极化将电磁屏蔽效能提升至44.6 dB。这种物理致密化工艺突破了传统单层薄膜中力学强度与导电性能负相关的限制,但高导电MXene的过量使用导致表面反射较强(反射损耗为15.8 dB),在柔性穿戴场景中可能产生二次电磁污染。
为构建高吸收低反射的薄膜屏蔽材料,Wang等[37]通过将空心银纳米颗粒(H-AgNPs)与CNFs交织形成葡萄串状多级结构,空心结构产生的壳-空腔界面能够显著增加介电极化损耗。当AgNPs负载量为12 %时,148.8 μm厚度的薄膜能实现89.56 dB的高屏蔽效能,其中吸收损耗达79.03 dB,反射系数降至0.05以下。该研究通过多界面设计结构创新而非单纯增加填料含量来优化阻抗匹配。
2.2 双层结构膜材料
单层膜存在诸多不足。一方面,为提高屏蔽效能,往往需要增加导电填料的用量。然而这会导致填料分散性变差,难以在薄膜中均匀分布,进而影响导电网络的形成;膜的力学强度也会因填料过量而降低。此外,填料用量过高会降低阻抗匹配,反而不利于屏蔽效能的提升。双层结构通过增强界面相互作用与优化功能层组合,改善屏蔽材料的力学性能和柔性,同时提高屏蔽效能及吸收系数[38-39]。其由不同功能层如导电层、绝缘层、磁性层等堆叠而成,通过合理控制各层的厚度和顺序,改善屏蔽介质在自由空间状态下的阻抗特征,实现对电磁波的多次反射和吸收,进而达成高效的电磁屏蔽效果,不同功能层之间的协同作用还可以充分发挥各层材料的优势,增强材料的综合性能。
Mai等[40]利用磁性金属骨架(CZIF),采用两步真空辅助过滤法制备了CZIF/MXene/CNFs复合纸,并在此基础上形成了上层为高导电性反射层,下层为高磁性吸收层的双层结构。当CZIF/MXene/CNFs的质量比为1∶3∶1时,吸收层方向入射的屏蔽效能最高达62.5 dB。不同入射方向对同组分样品的吸收系数有显著影响,从高磁性吸收层入射时,阻抗匹配改善,表面反射减弱,这归因于丰富的界面结构和高磁性的纳米颗粒促进了对电磁波的吸收。随MXene含量的增加,吸收损耗从30.0 dB增加至41.4 dB,而反射损耗基本保持不变。CZIF/MXene/CNFs的质量比为1∶3∶1时薄膜拉伸应力为12.8 MPa,在60 ℃条件下弯曲50次后电磁屏蔽效能仍能保持82.5%,CNFs的引入提高了复合材料的力学性能和耐久性,有望应用于小型化、便携式电子设备的电磁屏蔽领域。
目前,导电填料与磁性填料的协同效应在多层复合结构体系中备受关注[41-42]。如何精准调控其种类、含量与分布,以实现更优的阻抗匹配和更强的电磁屏蔽能力,仍需进一步研究。Guo等[43]利用钴镍金属有机框架(CoNi-MOF-74),通过两步真空辅助过滤法成功制备了具有Janus结构的CoNi-MOF-74/CNF-MXene/CNFs多功能双层膜。功能填料的合理排布改善了阻抗失配,促进入射电磁波进入薄膜,Janus结构的复合薄膜可形成“吸收-反射-重吸收”的屏蔽行为,有效延伸电磁波传播通道,提升屏蔽性能。当MXene质量分数为90%时,复合膜厚度为0.1 mm的轻质复合膜平均屏蔽效能达到68.86 dB,在环境大气中放置15 d后其总屏蔽效能仍能达到43.4 dB。此外,较强的氢键相互作用和紧密的界面结合使复合膜具有较好的柔性,这些使该双层膜在极端条件下的可穿戴和小型化电子器件中展现应用潜力。然而,MXene质量分数过高时,电磁屏蔽机制从以吸收为主转变为以反射为主,反射系数过高。
双层结构材料具有各向异性屏蔽性能、较高的力学性能和耐久性等优势,还可以优化其材料组成和结构设计,从而有效降低电磁波反射率。具体而言,通过引入梯度结构设计和多元损耗机制,实现材料表面阻抗的渐进匹配,达到优异的电磁屏蔽性能。
2.3 梯度结构膜材料
受自然界启发,许多生物结构展现出梯度变化的特性,梯度结构是指材料内部的组成、结构或性能在某个方向上呈连续或交替变化的分布状态。这种功能和结构的梯度变化启发到导电聚合物复合材料的结构设计中,让材料从外到内对电磁波进行不同程度的吸收、反射或诱导[44],从而提升电磁屏蔽能力。
Mai等[45]通过原位外延生长和热裂解制备了MOFs衍生的钴空心碳笼(Co-HCC),再交替沉积不同质量分数CNFs/Co-HCC和MXene/CNFs薄膜,制备出MOFs/MXene/CNFs复合薄膜。该薄膜呈现梯度交替的电磁结构,产生梯度阻抗匹配。随着MXene质量分数的梯度递增和CNFs/Co-HCC质量分数的梯度递减,材料的前层对电磁波的吸收能力增强,而后层的反射能力提升。大量存在的异质界面为电磁波传播提供了多重散射中心。MXene质量分数为57.1%的3层和5层复合膜的屏蔽效能分别可达到35.3 dB和45.6 dB,远大于相同组分单层共混膜(13 dB)的电磁屏蔽能力,吸收系数也更高。5层复合膜在X波段(45.6 dB)、Ku波段(36.0 dB)、K波段(60.9 dB)和Ka波段(66.8 dB)表现出优异的电磁屏蔽性能,有助于适应各领域对电磁屏蔽频谱的特定要求,但缺少部分力学性能测试结果。
在导电聚合物复合材料中,大量导电填料使薄膜厚度增加,导致力学性能下降,因此对于超薄柔性电磁屏蔽膜的开发需要探索。Hu等[46]通过化学沉积法制备还原氧化石墨烯负载四氧化三铁(rGO/Fe3O4)后,将CNFs/rGO/Fe3O4分散液和CNFs/银纳米材料(AgNMs)分散液按比例划分多份,交替沉积成多层纳米复合薄膜。若薄膜沉积层数过多,则因分散液划分份数过多而致使导电网络被削减,电导率降低,但电磁屏蔽性能因更好的界面极化损耗、磁损耗而提升。在保持分散液总量和组分不变的情况下,厚度为67 μm的非对称梯度交替6层纳米复合薄膜的屏蔽效能较好,高达112.9 dB。力学性能表现上,该薄膜具有115.2 MPa的拉伸强度和8.1%的断裂应变,可以随意弯曲和打结,达到超薄、柔性和有效的热管理,但该复合膜也存在一些问题,其反射系数远大于吸收系数,表明复合膜仍是反射主导的电磁屏蔽材料,仍会导致显著的二次辐射问题。
为有效平衡良好电磁屏蔽性能与低反射间的矛盾,Guo等[47]利用MXene负载钴铁氧体(CoFe2O4/MXene),制备了具有电磁双梯度结构的CoFe2O4/MXene/AgNWs/CNFs复合薄膜,CoFe2O4_MXene/CNFs作为阻抗匹配层沉积在薄膜顶部3层,AgNWs/CNFs作为高效屏蔽层沉积在薄膜的底部。通过调节阻抗匹配层中CoFe2O4和MXene的比例,可以实现正的电导梯度和负的磁导梯度,多种损耗机制使复合薄膜具有低反射特性。研究发现增加电磁梯度、AgNWs质量分数和反射层厚度,都能提升复合薄膜的屏蔽效能;而增加吸收层厚度,可显著降低反射系数,增强吸收特性。当CoFe2O4在阻抗匹配层的质量分数分别为90、50、30%、AgNWs质量分数为50%时,复合薄膜的屏蔽值最高达84.3 dB,反射系数为0.42,屏蔽机制以吸收为主导。AgNWs为30%的复合薄膜,拉伸强度达128.2 MPa,拉伸应变达5.34%,获得了在电磁屏蔽性能和力学性能方面表现优异的低反射材料。
梯度结构的CNFs基电磁屏蔽材料在开发高吸收、低反射且兼具优异力学性能的电磁屏蔽材料方面展现出显著优势,不同功能材料制成的梯度结构薄膜如表1所示。在性能拓展方面,响应性梯度结构可作为新兴研究方向。通过引入对温度、电场、磁场等外界刺激具有响应特性的功能材料,梯度结构材料可实现电磁屏蔽性能的智能调控,从而适应复杂多变的电磁环境,但在梯度材料的制备过程中,实现功能填料浓度的精确梯度分布仍面临挑战;因此,在制备技术上需重点关注材料性能的一致性和可重复性,以进一步提升其实际应用潜力。对于多层薄膜,可注重在轻质和柔性方面的改善。
表1 纤维素基梯度结构薄膜的性能参数、适用场景等
Tab.1
| 功能材料 | 厚度/μm | 电磁屏蔽 效能/dB | 反射系数 R | 力学强度/ MPa | 适用领域 | 参考 文献 |
|---|---|---|---|---|---|---|
| Co-HCC/MXene/CNFs | 200 | 45.6 | 0.25 | — | 6G通信、电子设备电磁屏蔽 | [45] |
| CNFs/rGO/Fe3O4/AgNWs | 67 | 112.9 | — | 115.2 | 可穿戴电磁屏蔽设备 | [46] |
| CoFe2O4/MXene/AgNWs/CNFs | 100 | 84.3 | 0.42 | 128.2 | 极端环境电子设备、个人热管理 | [47] |
| CNF/MXene/AgNWs | 35 | 65.4 | — | 194.3 | 航空航天、可穿戴设备 | [48] |
| CNF/MXene/Fe3O4/CNTs | 18 | 66.0 | 0.97 | — | 户外便携式设备、航空航天 | [49] |
| CNT/CNF/PEDOT∶PSS | 150 | 61.5 | — | — | 通信工程、航空航天 | [50] |
注:Fe3O4/CNTs为碳纳米管负载四氧化三铁,PEDOT∶PSS为聚(3,4-乙烯二氧噻吩)∶聚苯乙烯磺酸盐。
3 纤维素基电磁屏蔽气凝胶材料
3.1 单层结构气凝胶材料
气凝胶具有超高孔隙率(>90%)和超低密度(0.001~0.5 g/cm3),电磁屏蔽机制主要依靠多孔结构引起的电磁波散射和吸收效应。其具备的高孔隙率和丰富孔道结构能够有效延伸电磁波的传播轨迹,增加电磁波的损耗。
在气凝胶研究领域,注重提升气凝胶的稳定性和电导率。Ma等[53]结合真空辅助过滤与液氮预冻的方法制成了具有孔泡结构的MXene/CNFs复合气凝胶薄膜,通过蜂窝结构设计建立了更多的孔隙。调控MXene与CNFs的比例,发现在二者质量比为9∶1时,气凝胶膜的屏蔽效能最高可达54 dB,优于未经液氮处理的同组分砖泥结构薄膜(48 dB)。对照未经液氮处理的薄膜,MXene/CNFs气凝胶薄膜的电导率下降,这是由于蜂窝网络使MXene的连接减少,但具有均匀孔隙的蜂窝状结构有利于反射和吸收电磁波,使气凝胶薄膜的屏蔽性能不减反增。
为制备高孔隙率、低生产成本和表面功能化的电磁屏蔽复合材料,Zhu等[54]制备了轻质(密度小于0.075 g/cm3)、多孔(孔隙率大于95.47%)的纤维素纳米纤维/碳纳米管/阳离子纤维素纳米晶体/海藻酸钠(CNFs/CNTs/CCNC/SA)气凝胶。在体积不变的条件下比较发现,气凝胶密度随CNTs含量增加而增加,更多的CNTs填充孔隙,限制孔的分布和尺寸,孔隙率降低。当CNTs质量分数为89%时,在X波段样品的总屏蔽性能最高达39.8 dB,比屏蔽效能为537.5 dB·cm3/g,且由于气凝胶的高孔隙率,电磁波能以低反射率穿透气凝胶,随后被限制在孔隙中,被CNTs层衰减和散射,最终被吸收并转化为热量耗散,因此在X波段频率范围内,该复合气凝胶以吸收为主要屏蔽机制,但该研究仅通过冷冻干燥控制孔隙,未探索梯度孔隙、各向异性孔隙等结构对电磁波传播路径的定向调控潜力。
气凝胶研究的前沿方向之一是通过调控微观结构提高屏蔽性能,深入研究气凝胶孔壁空隙界面数量、孔隙形状和尺寸等微观结构因素对电磁屏蔽性能的影响规律,有助于设计出更高效的单层气凝胶屏蔽材料[55]。Zeng等[56]采用简易的冷冻铸造自组装的方法,通过双向冷冻、单向冷冻、随机冷冻制备了呈现层状、蜂窝状、无规多孔结构的CNFs/AgNWs气凝胶。对比其在2 mm条件下的电磁屏蔽性能,由于高数量单元壁所引起的电磁波多次反射,层状气凝胶的屏蔽效能值更高,达到70.5 dB,比屏蔽效能高达178 235 dB·cm3/g,蜂窝状气凝胶屏蔽效能值为60.6 dB,随机冷冻气凝胶屏蔽值为54.8 dB。同时,对层状气凝胶进行垂直于层状方向的压缩,制得0.03 mm的薄膜,材料的孔隙率从0.997减小到0.827,吸收损耗减小,进一步表明层状多孔结构有利于提高屏蔽性能。在力学性能上,持续不断的孔壁数量越多,该方向上测得的强度和模量越高。
单层气凝胶可在微观结构的均匀性上进行提升,减少部分气凝胶性能波动。后续研究可尝试采用新的模板法或自组装技术,精确控制气凝胶的微观结构,提高性能的一致性。同时,可以考虑利用3D打印技术制备定制化结构的CNFs基电磁屏蔽材料[57],设计出具有特定孔隙率、孔径分布和内部结构的材料,使电磁波在材料内传播更加均匀,有利于电磁屏蔽性能和强度提升。
3.2 双层结构气凝胶材料
基于“吸收-反射-再吸收”多重屏蔽机制的双层气凝胶设计,通过结构分层优化电磁波耗散路径,可显著降低材料表面反射率并提升整体屏蔽效能。
Wang等[58]通过定向冷冻法构建了Fe3O4/CNTs/水性聚氨酯(WPU)/CNF气凝胶与镀银泡沫的双层复合材料,利用气凝胶的阻抗匹配特性增强电磁波吸收,结合反射层的高导电性实现多重反射衰减。其屏蔽效能达62.81 dB,且反射系数仅为0.141。尽管双层结构已展现出优异的低反射特性,但单一功能层的电磁损耗机制存在局限性。为此,研究者进一步引入磁性组分与多功能协同设计,以扩展双层结构的应用场景。
Mai等[59]利用钴镍中空碳纳米笼(CoNi-HCN),通过两步冷冻法制备CoNi-HCN/CNFs-MXene/CNFs双层气凝胶,两层间通过氢键紧密结合。上层的CoNi-HCN与CNFs协同吸收电磁波,减少表面反射;下层MXene将剩余电磁波反射回上层,层间通过反射、界面极化和传导损耗消耗电磁波,双层结构协同实现高效电磁屏蔽。改变MXene与CoNi-HCN的比例,比较得到随着CoNi-HCN质量分数的增加,材料的电磁波吸收特性呈增强趋势,但MXene质量分数过低导致屏蔽值过低,因此探讨组成部分的比例以实现高屏蔽与低反射之间的平衡非常重要,该材料最高可实现35.1 dB的屏蔽效能,反射系数为0.25。在优化电磁损耗机制的同时,研究者可进一步关注结构参数对性能的影响,以实现更精细的性能调控。
Ma等[60]将薄膜的轻薄、紧密特性与气凝胶的高孔隙率、高效吸收特性相结合,利用铁钴层状双金属氧化物(FeCo-LDO)制备了CNFs/rGO复合膜和CNFs/rGO/FeCo-LDO气凝胶复合材料。探究了薄膜厚度(0.2~0.8 mm)和气凝胶质量分数(0.5%~2.0%)对屏蔽性能和吸收系数的影响。在厚度为0.8 mm、质量分数为1.0%时薄膜电的磁屏蔽性能最好,总屏蔽效能值从39 dB提升至65 dB,吸收系数可达0.68,实现以吸收为主的屏蔽材料。此外,压缩率通过调控孔隙结构影响吸收效率,适度压缩(10%~30%)可优化多重反射路径,有助于提升吸收性能。此研究为双层结构的可控制备与应用提供了关键参数指导,但仅研究了该材料特定频段的电磁屏蔽性能,在5G乃至未来6G通信等高频应用场景下的性能表现未知。
3.3 梯度结构气凝胶材料
梯度结构设计通过调控电磁波在材料内部的传播路径与能量耗散方式,可突破传统均质气凝胶因单一孔隙结构和阻抗失配问题。Wei等[62]通过浸渍、干燥和碳化工艺在纤维素纸基碳支架中构建了Fe3O4纳米颗粒的双向梯度分布,使磁性颗粒在材料厚度方向和平面方向形成非对称梯度。材料层间形成“高磁-低磁-中磁”梯度,通过调节导电网络与磁性颗粒的协同作用增强界面极化与磁损耗,显著提升电磁屏蔽性能,总屏蔽效能达49.3 dB,SSE与d比值达1 805.9 dB/(cm2·g),同时降低了反射系数0.23。该研究展示了成分梯度设计在平衡高屏蔽效能与低反射污染中的潜力,但仍需解决材料力学强度受孔隙率制约与宽频吸收能力的不足。
Mao等[63]通过冰晶溶解和常压干燥策略制备了具有“有序-有序-无序”不连续孔隙梯度结构的CNFs基气凝胶,为气凝胶的孔隙结构设计提供了新方法。其屏蔽机制基于其独特的3层结构,层1中孔径为120 μm有序大孔和弱介电特性优化了气凝胶与空气界面的阻抗匹配,促进电磁波入射;层2中孔径为40 μm有序小孔随MXene浓度增加,能有效吸收透过层1的电磁波,且层2与层3间的孔隙尺寸和取向的不连续变化增强了多次反射/散射行为,进一步消耗电磁波;层3的无序孔结构(平均孔径小于345 μm),在高电导率AgNWs的作用下,改变电磁波传播方向,延长其在材料内部的传输路径,实现高效屏蔽。该气凝胶在L、S、C、X、Ku的超宽波段实现了90 dB以上的电磁屏蔽性能。其不连续的孔梯度结构实现了约0.2的超低反射系数,有效减少了二次电磁辐射污染。
4 结束语
本文系统总结了纤维素纳米纤维(CNFs)基复合材料在电磁屏蔽应用中的最新研究成果,重点分析了多维结构设计策略与材料屏蔽性能之间的关系。层状结构、梯度结构、多孔结构、复合结构的设计策略各具特点,有效提升材料的综合屏蔽效能。尽管纤维素基电磁屏蔽复合材料已取得显著研究成果,但仍有诸多方面有待进一步探索与发展。
1)深入研究导电填料与磁性填料的协同作用机制,精准调控其在复合材料中的分散状态和相互作用,以实现更优的阻抗匹配和更好的损耗能力,提升电磁屏蔽性能。
2)开发低反射的CNFs基电磁屏蔽复合材料,减少二次反射污染。构建复合结构,将不同特性的材料结合,利用界面极化和多重散射机制增强电磁波的吸收。
3)提高CNFs基复合材料的力学性能和耐久性,可通过优化结构设计和添加增强相,提高材料在长期应力作用下的结构完整性和电磁屏蔽效能保持率。
4)探索智能响应结构在CNFs基复合材料中的应用,满足不同场景下的多样化需求。
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Ultralight and highly flexible biopolymer aerogels, composed of biomimetic cellular microstructures formed from cellulose nanofibers and silver nanowires, are assembled a convenient and facile freeze-casting method. The lamellar, honeycomb-like, and random porous scaffolds are successfully achieved by adjusting freezing approaches to modulate the relationships between microstructures and macroscopic mechanical and electromagnetic interference (EMI) shielding performances. Combining the shielding transformation arising from compression and the controlled content of building units, the optimized lamellar porous biopolymer aerogels can show a very high EMI shielding effectiveness (SE), which exceeds 70 or 40 dB in the X-band while the density is merely 6.2 or 1.7 mg/cm, respectively. The corresponding normalized surface specific SE (defined as the SE divided by the material density and thickness) is up to 178235 dB·cm/g, far surpassing that of the so-far reported shielding materials. Antibacterial properties and hydrophobicity are also demonstrated extending the versatility and application potential of the biopolymer hybrid aerogels.
Advancements in 3D-printed architectures for electromagnetic interference shields
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DOI:10.1039/D3TA07181B
URL
[本文引用: 1]
This paper offers a comprehensive overview of 3D-printed electromagnetic shielding. It covers principles, simulation/testing, 3D printing techniques, materials, and function-oriented shields. It also discusses challenges and future development.
Fe3O4@CNTs/WPU@CNF aerogel/Ag foam composites with a double-layer structure for absorption-dominated electromagnetic shielding performance
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Zeolitic imidazolate frameworks derived magnetic nanocage/MXene/nanocellulose bilayer aerogels for low reflection electromagnetic interference shielding and light-to-heat conversion
[J].DOI:10.1002/adfm.v35.13 URL [本文引用: 1]
Double-layer of CNF/rGO film and CNF/rGO/FeCo-LDO aerogel structured composites for efficient electromagnetic interference shielding
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A scalable,efficient,and facile ambient drying approach for preparing low shrinkage,compressive,and superporous nano-cellulose-based aerogels via a physicochemical crosslinking strategy
[J].
DOI:10.1039/D4GC05106H
URL
[本文引用: 1]
A nanocellulose-based aerogel with a low volume shrinkage was prepared via a physicochemical crosslinking strategy without specialized equipment, high energy consumption, and generation of waste organic solvents.
Cellulose-derived carbon scaffolds with bidirectional gradient Fe3O4 distribution:integration of green EMI shielding and thermal management
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Atmospheric pressure dried discontinuous pore gradient structured CNF-based aerogel for ultra-low reflection,broadband,and super-high EMI shielding
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