为应对这一挑战,科学家们将目光转向了人体日常活动期间最丰富的能源形式——机械能。人们每天都在重复大量无规则的低频运动,如果将这些耗散的机械动能转化成可供利用的电能,将为个人可穿戴设备的发展开辟新纪元。在多种机械能发电模式中,摩擦纳米发电机(TENG)凭借廉价易得、分布广、功率高、集成度高、安全性高等特色脱颖而出,成为最具代表性的机械能发电机[16-17]。王中林团队于2012年首创摩擦纳米发电技术,该技术利用摩擦电器件的接触起电和静电感应耦合效应,在外电路产生可用的交变电流[18];随后,该团队于2014年率先开发出用于可穿戴设备供能的摩擦电织物,自此关于摩擦电织物的学术研究得到了长足发展[19]。
随着摩擦纳米发电技术的不断成熟,摩擦电纺织品凭借其优良的特性逐渐成为功能性发电织物领域的研究重点,其在可穿戴能源供给中的占比逐年增长,总体上呈现出巨大的发展潜力和广阔的应用前景。本文从机制、材料、结构和功能性等方面展开,系统阐述了摩擦电技术的基本理论、摩擦电纤维的分类与应用,并以此为基础分析了目前该领域的困境与未来的发展方向,以期为摩擦电纺织品的学术研究和产业转化提供一些有启发意义的思考。
1 摩擦电技术的起源
从1820年奥斯特发现电流可以使小磁针偏转 [20]开始,到1861年麦克斯韦系统性地总结了前人的研究成果,提出了麦克斯韦方程组,自此进入电磁波时代。1885年,海维赛德将麦克斯韦方程组由20个方程简化为今天所熟知的4个矢量方程,揭示了变化的磁场如何产生电场,变化的电场又是如何产生磁场的。在之后的100多年中,麦克斯韦方程组的形式基本保持不变。
图1
图1
电磁辐射与TENG的能量转换过程
图中:d为2个介电层之间的距离,cm; v为介电层张开的速度,cm/s。
Fig.1
Energy conversion process between electromagnetic radiation and TENG.
(a) Initial state; (b) Angle between dielectric layers increases; (c) Angle between dielectric layers reaches maximum state
2 摩擦起电的物理机制
图2
图2
TENG的4种工作模式
Fig.2
Four operating modes of TENG. (a) Vertical contact separation mode; (b) Horizontal sliding mode; (c) Single electrode mode; (d) Independent layer mode
研究人员发现,在4种工作模式中,TENG均需要通过摩擦才可产生静电荷。这是因为2种摩擦极性材料间的接触距离只有小于原子斥力区时,电荷转移现象才会在2种材料界面间发生[27]。材料间的相互摩擦提供外界作用力,使得2个材料表面在原子或纳米尺度上产生局部高压,从而促使电子云或波函数发生重叠,此时电子可在不同材料表面间进行转移。图3示出2个原子间的原子相互作用势[28],其中F表示作用力。如图3(a)所示,当 2种不同材料的原子形成化学键时,它们的电子云有小部分发生重叠,此时原子处于平衡状态,其键长或原子间距离等于平衡距离a[28]。当2个原子的电子云重叠区域增加时,它们处于相互排斥状态,其键长或原子间距离d小于平衡距离a,此时材料间易发生电子转移(见图3(b))。一旦原子间距离d大于平衡距离a,2个原子处于相互吸引状态,它们的电子云将不再重叠,此时材料间难以发生电子转移(见图3(c)),因此,摩擦外力是不同材料界面间发生电子转移的必要条件。
图3
图3
2个原子间的原子相互作用势
Fig.3
Interatomic interaction potential between two atoms. (a) Equilibrium position; (b) Repulsive region; (c) Attractive region
基于接触起电的广泛性和普适性,研究人员总结提出了接触起电的理论模型。图4示出不同材料间电子转移和释放的电子云势阱模型[28]。如图4中a所示,当材料A的原子与材料B的原子相距较远时,它们之间无电子云重叠,因此不会发生电子转移现象[28]。此时势阱将电子束缚在特定轨道中,从而阻止它们的自由逃逸行为。如果施加外部压力,促使材料A和材料B相互靠近,它们将由2个单势阱转变为1个非对称双势阱,并且由于强烈的电子云重叠,它们间的势垒将下降。此时电子先在不同原子间转移,然后在同种原子中由高能级跃迁到低能级(见图4中b)。当2种材料分离后,转移的电子理论上将长期保留在材料表面,然而由于温度的作用,部分电子会产生热电子发射现象,从材料表面逃逸(见图4中c和d)。这种物理机制说明接触起电期间更大的外力将促使更多的表面发生这种原子级接触,从而诱导更多的电子发生转移。
图4
图4
用于解释2种不同材料间电子转移和释放的电子云势阱模型
Fig.4
Electron-cloud-potential-well model used to explain transfer and release of electrons between two different materials
3 摩擦电纺织品的研究进展
自从TENG被发明以来,摩擦电纺织品凭借其可持续性收集人体生物力学能量的优势,成为众多研究人员关注的焦点。通过纤维材料的制备和织物结构的设计,摩擦电纺织品被赋予了出色的功能性与智能性,并且可以像普通织物一样具备高柔软度、高贴合性、高耐用性、强适应性等特点,使其成为一种具有巨大应用潜力的物联网集成平台。TENG是摩擦电纺织品的理论基础,更是摩擦电纺织品进行科学研究和产业转化的基石。基于TENG宏观形态的不同,摩擦电纺织品可以分为三大类,即纱线基TENG、织物基TENG以及非织造布基TENG。
3.1 纱线基TENG
纱线基TENG是一种无需外界介质参与,单根纱线通过接触起电就可以产生摩擦静电荷,并可对静电荷进行高效收集的一种纳米发电机,其也是一种最小的摩擦电纺织品功能单元。根据结构和制备方法的不同,纱线基TENG可以分为包覆结构、缠绕结构以及内置螺旋结构。
基于不同的材料组成和结构设计,包覆结构纱线基TENG可分为叠层包覆与蛇形结构2种情况。Fu等[29]利用层层叠加的聚氨酯(PU)/碳纳米管(CNTs)/龙皮硅胶(dragon skin)作为芯纤维,然后将还原氧化石墨烯(rGO)/聚二甲基硅氧烷(PDMS)/银纳米线(AgNWs)作为鞘纤维管,从而制备得到叠层包覆的纱线基TENG。为提升纱线基TENG的输出与传感性能,研究人员在鞘纤维管内表面构建金字塔型微结构,使其可检测低至0.02 N的压力,并且灵敏度可达到26.75 V/N。由于结构的本征缺陷,叠层包覆的拉伸性一般较差。为进一步增强纱线基TENG的拉伸性能,Wang等[30]利用导电炭黑和CNTs在硅橡胶管壁上设计了一种蛇形附着电极结构,从而使得纱线基TENG具有高达150%的拉伸应变。该纤维可分别在拉伸、弯曲、扭转、压缩等变形方式下运行,在拉伸模式下,其最大开路电压可达63 V。
包覆结构纱线基TENG的电极材料一般使用金属或碳材料,在人体频繁运动时,其导电网格往往会被破坏,循环稳定性亟需进一步提升。与包覆结构相比,缠绕结构纱线基TENG常常利用弹性体作为基底,然后将功能纤维缠绕于其上,因此其耐用性一般较强。Chen等[31]以弹性体聚合物PU作为基底,以AgNWs包覆的锦纶(PA)作为内电极缠绕于基底上,以超弹性硅橡胶(Ecoflex)作为摩擦介质层共同构成了芯纤维;然后将铜(Cu)导线缠绕于芯纤维上构成了鞘纤维层。该缠绕结构纱线基TENG可长期在高应变的状态下运行,并且可以与人机交互系统相结合,精确控制商用灯、风扇、泵以及计算机软件。除使用上述宏观纤维进行缠绕以外,Zhang等[32]通过共轭静电纺丝法在芯纤维基底上进行纳米尺度加捻,从而制备了另一种缠绕结构纱线基TENG。该纱线基TENG以导电纤维包覆的PU作为芯层,以加捻的偏二氟乙烯-三氟乙烯共聚物(P(VDF-TrFE))纳米纤维作为鞘层,其拉伸应变高达200%。此外,这种纳米加捻促使该纱线基TENG具备超高的耐磨性,在5 000次马丁代尔磨损测试中表现出优异的稳定性。
近年来,在上述结构的基础上,Gong等[33]开发了一种全新的内置螺旋纱线基TENG。首先以导电纱线为基底将PA缠绕在其上构筑了芯纤维;然后,以硅橡胶管为基底,将竹纤维缠绕在其上构筑了鞘纤维管;最后,利用鞘纤维管的内摩擦力以及端口的挤压力构成了内置螺旋结构,其拉伸应变高达300%。2019年,Gong等[34]基于上述原理,利用改进的熔融挤出工艺,连续化地制备了内置螺旋纱线基TENG。该纤维是一种水陆两栖纤维,并且利用水分子的极化弛豫特性,其在水中的输出性能远高于空气中,且该纤维也是一款可连续化生产的纱线基TENG。2021年,Yang等[35]将荧光材料应用于内置螺旋纱线基TENG上,在拉伸期间该纤维可同时输出电信号与光信号。将该纤维制备成智能手套,其可驱动机械手和虚拟手。基于前期的研究工作,2023年,Wang等[36]制备了一种超细的交互式内置螺旋纱线基TENG,并利用该纤维构筑了一种电子织物键盘,从而实现无线控制智能手机的目的。
3.2 织物基TENG
纱线基TENG的2个摩擦介质层一般被封在纤维内部,其受到外界温湿度等因素的影响相对较小,然而其需要复杂的结构设计与材料选择。与纱线基TENG相比,织物基TENG的结构较为简单;材料选择面广,更易与传统服装集成。虽然织物基TENG更易受到外界环境的影响,但它的高集成度对于摩擦电纺织品的推广应用具有重要意义。根据织物编织方式的不同,织物基TENG可以被归纳为机织型和针织型2类。
Zheng等[37]以Cu包覆的聚对苯二甲酸乙二醇酯(PET)纤维作为经纱,然后将聚酰亚胺(PI)包覆的这种纱线作为纬纱,最后通过机织法将这2种织物基TENG编织成织物。在该织物基TENG中,Cu既是摩擦介质层,也是电极层,而每处经纬纱交织点均为1个小的TENG,从而实现了对人体微弱运动信号的响应。此外,基于热拉伸工艺,Jia等[38]利用聚丙烯和金属钨丝制备了一种长达百米的包芯纱,并用此包芯纱和锦纶分别作为纬纱和经纱,制备了一种单电极的机织型TENG。该TENG的功率密度可达43 mW/kg,经过10万次循环测试和5次洗涤后,其电学输出性能依然保持稳定。随着摩擦电技术的日新月异,研究人员不再满足于仅获得交流电信号,希望得到实用性更强的直流电信号。为此,Chen等[39]巧妙地利用衣服中有害且烦人的静电击穿现象,制备得到了一种有趣的机织型直流TENG。该直流TENG由聚酰胺绝缘纱和聚酰胺镀银导电纱组成,其中经纱完全是绝缘纱,纬纱由绝缘纱和导电纱的复合纱线构成。在1根复合纱线中,2根导电纱分别作为摩擦极性材料和静电击穿电极,然后利用绝缘纱将2根导电纱物理隔离开。当直流TENG的长宽分别为3.5和 1.5 cm 时,其可以轻松点亮416个发光二极管;当直流TENG的长宽分别为7和6.8 cm时,其开路电压和短路电流分别高达4 500 V 和40 μA。优异的直流电性能促使该直流TENG可为温湿度计等电子元器件持续供电。
除上述织物中纤维间摩擦起电外,织物基TENG还可实现织物间摩擦起电。Chen等[40]以棉纱作为经纱分别织制了2块机织物,其中1块以棉纤维和聚四氟乙烯(PTFE)纤维区域交替形式构筑,另一块以棉纤维和碳纤维的的区域交替形式构筑。与接触分离式的TENG不同,织物基TENG组成的这种摩擦电纺织品是一种平面滑动TENG,其电流随滑动速率提升而增加,而开路电压和短路电荷则始终维持在118 V和48 nC。
与上述机织型TENG类似,针织型TENG也可分为纤维间摩擦起电和织物间摩擦起电。与机织型TENG不同的是,针织型TENG具有更优异的透气性、拉伸性以及柔软度,穿戴者的舒适感会更好。Fan等[41]分别以锦纶和涤纶包覆的导电纤维为摩擦介质层,从而制备得到单电极摩擦电纤维。然后,将该摩擦电纤维编织为开衫针织物,其具有极高的传感灵敏度(7.84 mV/Pa)和响应速度(20 ms),并且可以在10万次循环运行时保持稳定。此外,该针织型TENG可直接与颈部、手腕、脚踝、腹部和胸部等地方的织物相结合,其对普通织物的适应性和集成度非常高。在纤维间摩擦起电的针织型TENG中,除常见的二维结构,如今三维织物结构也越来越受到研究人员的青睐,采用双针床横机技术编织了一种三维双面互锁的针织型TENG[42]。该针织型TENG由棉纱和锦纶纱线复合而成,具有优异的弹性、透气性与拉伸性,可用作三维触觉传感器。
此外,在织物间摩擦起电的针织型TENG中,研究人员也开展了大量的研究工作。Dong等[43]分别利用锦纶66(PA66)缠绕的镀银导电纤维和PTFE缠绕的镀银导电纤维制备了2种摩擦电纤维,其中PA66和聚四氟乙烯(PTFE)分别为摩擦正极和负极材料,并使用这2种摩擦电纤维进一步构筑了针织物。当该针织物的面积达到64 cm2时,其内部将具有2 160个线圈,透气率可达到1 491.1 mm/s。此外,在拉伸和压缩期间,该针织物均可发电,在110%的拉伸应变下其开路电压可达32 V。除上述接触分离式的工作模式以外,科研人员也在滑动式的模型中进行了大量的研究工作。Huang等[44]以镀银锦纶纱线作为摩擦正极材料和电荷收集器,以棉纱线作为间隔材料,制备了一种滑动式的针织型TENG。该针织型TENG可完美融合进传统服装中,从而最大限度地保留服装的质量轻、可洗性好以及穿着舒适的优点。更重要的是,经过织物纹理的精心设计,该针织型TENG可以在工业生产线上放大生产。
3.3 非织造布基TENG
有别于上文所述的纱线基TENG和织物基TENG,非织造布基TENG具有更大的比表面积,因此对于摩擦起电来说其具有更多的原子级接触区域。根据非织造布基TENG的功能性差异,可将其分为防水透湿型、吸湿排汗型以及高效抗菌型3类。Li等[45]基于静电纺丝和炭化工艺分别制备了PU、碳以及聚偏二氟乙烯(PVDF)纤维膜,然后以聚二甲基硅氧烷(PDMS)为黏合剂将上述3种纤维膜紧密贴合,最终制备得到柔软透气的非织造布基TENG。该TENG在50%的拉伸应变以内,其传感性能和力学性能均维持恒定,具有优异的柔软度和稳定性。此外,该TENG的孔径(1.08 μm)介于水滴(100 μm)和水分子(0.000 4 μm)之间,即水滴无法通过而水分子可以轻松穿透,因此其具有优异的防水透湿性。此外,该非织造布基TENG可以广泛地应用于智能机器人、交互式设备、人工假肢等领域。
防水透湿是非织造布基TENG的一个重要特性,但是对于流汗的皮肤而言却远远不够,大量汗液的出现可能会致使皮肤产生黏稠等不舒适的感觉。为克服这一难题,Yang等[46]分别使用P(VDF-TrFE) 和PA6作为摩擦负极和正极材料制备了吸湿排汗型非织造布基TENG。该TENG的吸湿排汗层由聚丙烯腈(PAN)和PA6纳米纤维组成,初步利用拉普拉斯压差促进体表汗液排放。为进一步提升非织造布基TENG的排汗能力,Gong等[47]以锦纶网、纤维素膜、PA6纤维膜、偏氟乙烯和三氟乙烯的共聚物P(VDF-TrFE)纤维膜以及多孔海绵制备了一种新型的芯吸极化型非织造布基TENG。该非织造布基TENG将主动摩擦电场极化与被动吸湿排汗相结合,可将大尺寸的水团簇转换为小尺寸的水团簇或水单体,极大地促进了汗液的扩散与蒸发,有力地保障了人体舒适性。此外,由该TENG制备得到的智能鞋垫,可迅速排干体表汗液,并实现0.8 ℃的降温效果。
除导致人体不舒适以外,汗液也可能造成皮肤瘙痒与炎症。为解决这一问题,Peng等[48]利用聚乙烯醇(PVA)、AgNWs以及聚乳酸-乙醇酸共聚物(PLGA)纳米纤维膜制备了一种抗菌非织造布基TENG。该TENG一方面为湿热传递提供了多级纤维毛细通道;另一方面对大肠杆菌和金黄色葡萄球菌表现出显著的抗菌活性,灭杀效率分别达到54%和88%,可有效地抑制细菌生长。此外,该非织造布基TENG的峰值功率密度达到130 mW/m,压力灵敏度为0.011 kPa-1,是一种优异的可穿戴自供能传感器,可应用于电子皮肤、人工智能等领域。
4 结束语
近年来,随着可穿戴技术的不断涌现与摩擦电技术的日趋成熟,摩擦电纺织品异军突起,凭借其对生物力学能量的高效收集,已成为随身能源领域的一匹黑马。摩擦电纺织品的蒸蒸日上与全世界众多研究人员对其材料、结构的不断改进与创新紧密相关,也与科学家们持续地挖掘摩擦起电机制,以及接连开发摩擦电纺织品的舒适性与功能性密不可分。同时其它相关研究领域的不断发展也进一步促进了摩擦电领域的茁壮成长。此外,测试标准的不断规范与评价标准的逐渐统一,也是推动摩擦电纺织品崛起的重要力量。
尽管目前摩擦电纺织品在能源供给、功能性、舒适性、耐用性等方面取得了一定的进步,但仍存在一些问题值得深思与探讨。与传统纤维相比,现阶段的摩擦电纤维由于功能层的叠加,其纤维直径往往较大,这限制了其与当前较为成熟的纺织工业体系相结合。这是因为在工业织机上,较粗、较硬的摩擦电纤维往往易折断,并且这种摩擦电纤维制备得到的织物一般柔软度和贴肤性也较差。此外,纱线基TENG、织物基TENG以及非织造布基TENG的本征缺陷也时刻制约着摩擦电纺织品的应用普及。纱线基TENG的封闭结构赋予了其独立性,但也限制其输出性能。织物基TENG的开放性导致其极易被外界环境因素所影响。通过静电纺丝技术制备的非织造布基TENG通常力学性能较差,难以承受人体的大幅度运动。
现有的摩擦电纺织品主要还是以学术研究为主,缺乏产业界的关注与介入,其产业转化之路仍然道阻且长。当前这些困难既需要摩擦电技术人员与纺织研究人员通力合作、共克时艰,也需要其它领域研究人员的大力配合。在电子信息与人工智能迅速发展的今天,集成电路、机器学习等技术的普及为摩擦电纺织品的发展提供了新的机遇,这将促使更细、更柔的摩擦电纤维可以承载更多的人体信息。在物理、化学、材料、纺织、服装、电子、计算机等领域专家的共同努力下,相信摩擦电纺织品一定会驶入快车道,为智能可穿戴设备保驾护航。
参考文献
Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis
[J].
Wearable biosensors for healthcare monitoring
[J].
DOI:10.1038/s41587-019-0045-y
PMID:30804534
[本文引用: 1]
Wearable biosensors are garnering substantial interest due to their potential to provide continuous, real-time physiological information via dynamic, noninvasive measurements of biochemical markers in biofluids, such as sweat, tears, saliva and interstitial fluid. Recent developments have focused on electrochemical and optical biosensors, together with advances in the noninvasive monitoring of biomarkers including metabolites, bacteria and hormones. A combination of multiplexed biosensing, microfluidic sampling and transport systems have been integrated, miniaturized and combined with flexible materials for improved wearability and ease of operation. Although wearable biosensors hold promise, a better understanding of the correlations between analyte concentrations in the blood and noninvasive biofluids is needed to improve reliability. An expanded set of on-body bioaffinity assays and more sensing strategies are needed to make more biomarkers accessible to monitoring. Large-cohort validation studies of wearable biosensor performance will be needed to underpin clinical acceptance. Accurate and reliable real-time sensing of physiological information using wearable biosensor technologies would have a broad impact on our daily lives.
Lab-on-skin: a review of flexible and stretchable electronics for wearable health monitoring
[J].
DOI:10.1021/acsnano.7b04898
PMID:28901746
[本文引用: 1]
Skin is the largest organ of the human body, and it offers a diagnostic interface rich with vital biological signals from the inner organs, blood vessels, muscles, and dermis/epidermis. Soft, flexible, and stretchable electronic devices provide a novel platform to interface with soft tissues for robotic feedback and control, regenerative medicine, and continuous health monitoring. Here, we introduce the term "lab-on-skin" to describe a set of electronic devices that have physical properties, such as thickness, thermal mass, elastic modulus, and water-vapor permeability, which resemble those of the skin. These devices can conformally laminate on the epidermis to mitigate motion artifacts and mismatches in mechanical properties created by conventional, rigid electronics while simultaneously providing accurate, non-invasive, long-term, and continuous health monitoring. Recent progress in the design and fabrication of soft sensors with more advanced capabilities and enhanced reliability suggest an impending translation of these devices from the research lab to clinical environments. Regarding these advances, the first part of this manuscript reviews materials, design strategies, and powering systems used in soft electronics. Next, the paper provides an overview of applications of these devices in cardiology, dermatology, electrophysiology, and sweat diagnostics, with an emphasis on how these systems may replace conventional clinical tools. The review concludes with an outlook on current challenges and opportunities for future research directions in wearable health monitoring.
Flexible fabric-based GaAs thin-film solar cell for wearable energy harvesting applications
[J].
Wearable power-textiles by integrating fabric triboelectric nanogenerators and fiber-shaped dye-sensitized solar cells
[J].
The charge transport characterization of the polyaniline coated carbon fabric as a novel textile based counter electrode for flexible dye-sensitized solar cell
[J].
Recent advancements in thermoelectric generators for smart textile application
[J].
Whole fabric-assisted thermoelectric devices for wearable electronics
[J].
Stretchable fabric generates electric power from woven thermoelectric fibers
[J].
Fabric-based self-pumping, single-stream microfluidic fuel cell
[J].
Passive direct methanol fuel cell using woven carbon fiber fabric as mass transfer control medium
[J].
The advanced polymer composite coated fabrics as an anode electrode and photocatalytic glucose micro fuel cell design
[J].
Recent progress of wearable piezoelectric pressure sensors based on nanofibers, yarns, and their fabrics via electrospinning
[J].
A review on PVDF nanofibers in textiles for flexible piezoelectric sensors
[J].
Recent progress of wearable piezoelectric nanogenerators
[J].
The current development and future outlook of triboelectric nanogenerators: a survey of literature
[J].
Triboelectric nanogenerators as a new energy technology: From fundamentals, devices, to applications
[J].
Flexible triboelectric generator
[J].
Woven structured triboelectric nanogenerator for wearable devices
[J].
面向工程电磁学的动生麦克斯韦方程组及其求解方法
[J].
Dynamic Maxwell equations for engineering electromagnetics and their solution
[J].
On Maxwell's displacement current for energy and sensors: the origin of nanogenerators
[J].
Toward the blue energy dream by triboelectric nanogenerator networks
[J].
Design optimization of soft-contact freestanding rotary triboelectric nanogenerator for high-output performance
[J].
Ambulatory cardiovascular monitoring via a machine-learning-assisted textile triboelectric sensor
[J].
Advances of high-performance triboelectric nanogenerators for blue energy harvesting
[J].
On the expanded Maxwell's equations for moving charged media system: general theory, mathematical solutions and applications in TENG
[J].
Excluding contact electrification in surface potential measurement using kelvin probe force microscopy
[J].
DOI:10.1021/acsnano.5b07418
PMID:26824304
[本文引用: 1]
Kelvin probe force microscopy (KPFM), a characterization method that could image surface potentials of materials at the nanoscale, has extensive applications in characterizing the electric and electronic properties of metal, semiconductor, and insulator materials. However, it requires deep understanding of the physics of the measuring process and being able to rule out factors that may cause artifacts to obtain accurate results. In the most commonly used dual-pass KPFM, the probe works in tapping mode to obtain surface topography information in a first pass before lifting to a certain height to measure the surface potential. In this paper, we have demonstrated that the tapping-mode topography scan pass during the typical dual-pass KPFM measurement may trigger contact electrification between the probe and the sample, which leads to a charged sample surface and thus can introduce a significant error to the surface potential measurement. Contact electrification will happen when the probe enters into the repulsive force regime of a tip-sample interaction, and this can be detected by the phase shift of the probe vibration. In addition, the influences of scanning parameters, sample properties, and the probe's attributes have also been examined, in which lower free cantilever vibration amplitude, larger adhesion between the probe tip and the sample, and lower cantilever spring constant of the probe are less likely to trigger contact electrification. Finally, we have put forward a guideline to rationally decouple contact electrification from the surface potential measurement. They are decreasing the free amplitude, increasing the set-point amplitude, and using probes with a lower spring constant.
On the origin of contact-electrification
[J].
DOI:10.1016/j.mattod.2019.05.016
[本文引用: 4]
Although contact electrification (triboelectrification) (CE) has been documented since 2600 years ago, its scientific understanding remains inconclusive, unclear, and un-unified. This paper reviews the updated progress for studying the fundamental mechanism of CE using Kelvin probe force microscopy for solid-solid cases. Our conclusion is that electron transfer is the dominant mechanism for CE between solid-solid pairs. Electron transfer occurs only when the interatomic distance between the two materials is shorter than the normal bonding length (typically similar to 0.2 nm) in the region of repulsive forces. A strong electron cloud overlap (or wave function overlap) between the two atoms/molecules in the repulsive region leads to electron transition between the atoms/molecules, owing to the reduced interatomic potential barrier. The role played by contact/friction force is to induce strong overlap between the electron clouds (or wave function in physics, bonding in chemistry). The electrostatic charges on the surfaces can be released from the surface by electron thermionic emission and/or photon excitation, so these electrostatic charges may not remain on the surface if sample temperature is higher than similar to 300-400 degrees C. The electron transfer model could be extended to liquid-solid, liquid-gas and even liquid-liquid cases. As for the liquid-solid case, molecules in the liquid would have electron cloud overlap with the atoms on the solid surface at the very first contact with a virginal solid surface, and electron transfer is required in order to create the first layer of electrostatic charges on the solid surface. This step only occurs for the very first contact of the liquid with the solid. Then, ion transfer is the second step and is the dominant process thereafter, which is a redistribution of the ions in solution considering electrostatic interactions with the charged solid surface. This is proposed as a two-step formation process of the electric double layer (EDL) at the liquid-solid interface. Charge transfer in the liquid-gas case is believed to be due to electron transfer once a gas molecule strikes the liquid surface to induce the overlapping electron cloud under pressure. In general, electron transfer due to the overlapping electron cloud under mechanical force/pressure is proposed as the dominant mechanism for initiating CE between solids, liquids and gases. This study provides not only the first systematic understanding about the physics of CE, but also demonstrates that the triboelectric nanogenerator (TENG) is an effective method for studying the nature of CE between any materials.
Fibrous self-powered sensor with high stretchability for physiological information monitoring
[J].
Sustainably powering wearable electronics solely by biomechanical energy
[J].
Flexible hierarchical helical yarn with broad strain range for self-powered motion signal monitoring and human-machine interac-tive
[J].
Abrasion resistant/waterproof stretchable triboelectric yarns based on fermat spirals
[J].
A wearable, fibroid, self-powered active kinematic sensor based on stretchable sheath-core structural triboelectric fibers
[J].
Continuous and scalable manufacture of amphibious energy yarns and textiles
[J].
Self-powered interactive fiber electronics with visual-digital synergies
[J].
Ultra-fine self-powered interactive fiber electronics for smart cloth-ing
[J].
Machine-washable textile triboelectric nanogenerators for effective human respiratory monitoring through loom weaving of metallic yarns
[J].
Scalable, washable and lightweight triboelectric-energy-generating fibers by the thermal drawing process for industrial loom weaving
[J].
Direct current fabric triboelectric nanogenerator for biomotion energy harvesting
[J].
DOI:10.1021/acsnano.0c00138
PMID:32181639
[本文引用: 1]
Triboelectric nanogenerators (TENGs) have demonstrated their promising potential in biomotion energy harvesting. A combination of the TENG and textile materials presents an effective approach toward smart fabric. However, most traditional fabric TENGs with an alternating current (AC) have to use a stiff, uncomfortable, and unfriendly rectifier bridge to obtain direct current (DC) to store and supply power for electronic devices. Here, a DC fabric TENG (DC F-TENG) with the most common plain structure is designed to harvest biomotion energy by tactfully taking advantage of the harmful and annoying electrostatic breakdown phenomenon of clothes. A small DC F-TENG (1.5 cm × 3.5 cm) can easily light up 416 serially connected light-emitting diodes. Furthermore, some yarn supercapacitors are fabricated and woven into the DC F-TENG to harvest and store energy and to power electronic devices, such as a hygrothermograph or a calculator, which shows great convenience and high efficiency in practice. This low-cost and efficient DC F-TENG which can directly generate DC energy without using the rectifier bridge by harvesting energy from unhealthy electrostatic breakdown has great potential as a lightweight, flexible, wearable, and comfortable energy-harvesting device in the future.
Traditional weaving craft for one-piece self-charging power textile for wearable electronics
[J].
Machine-knitted washable sensor array textile for precise epidermal physiological signal monitoring
[J].
3D double-faced interlock fabric triboelectric nanogenerator for bio-motion energy harvesting and as self-powered stretching and 3D tactile sensors
[J].
Seamlessly knitted stretchable comfortable textile triboelectric nanogenerators for E-textile power sources
[J].
Fabric texture design for boosting the performance of a knitted washable textile triboelectric nanogenerator as wearable power
[J].
All-fiber structured electronic skin with high elasticity and breathabi-lity
[J].
All-fiber tribo-ferroelectric synergistic electronics with high thermal-moisture stability and comfortability
[J].
Wicking-polarization-induced water cluster size effect on triboelectric evaporation textiles
[J].
A breathable, biodegradable, antibacterial, and self-powered electronic skin based on all-nanofiber triboelectric nanogenerators
[J].
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