柔性压阻压力传感器在可穿戴健康监测与机器人触觉感知中需求迫切，但其金属导电层通常依赖有毒钯/锡敏化-活化工艺、且一旦受损难以修复，开发无钯锡、可热修复的高性能柔性压阻传感材料具有重要意义。本文，成均馆大学（Jong-Woong Kim 团队）在《Advanced Science》发表名为”High-Performance Piezoresistive Sensors via Pd/Sn-Free Graphene-Catalyzed Metallization of Thermally Repairable Microfiber Scaffolds”的论文。研究提出了一种基于微纤维网络的压力传感器，该传感器同时满足这些关键要求，其主要重点在于一种多层制备方法：利用石墨烯作为介面层，在电纺聚合物纤维上进行无电解铜电镀。
具体而言，本研究采用电纺聚（ε-己内酯）（PCL）微纤维作为结构基础，利用其低熔点（约60°C）实现热辅助修复这一补充功能。与此同时，贴合的石墨烯/铜外壳旨在高温下保持纤维的整体形态和导电框架，从而将低温可修复性与高温结构稳定性区分开来。随后，通过无电镀沉积，在这些纤维上涂覆石墨烯和铜层，从而形成了一种坚固且导电的 PCL/石墨烯/铜 (PGC) 核-壳结构。引入石墨烯中间层是关键的设计创新，对制备过程和传感器性能都至关重要。将铜直接无电镀沉积到原始PCL纤维上，在根本上受到以下三个挑战的限制：
(1) 聚合物表面的惰性阻碍了有效的铜沉积；
(2) 铜与聚合物之间的界面附着力差，降低了结构稳定性；
(3) 在苛刻的化学活化条件下，聚合物网络容易受损。
石墨烯作为一种在化学和结构上均能紧密贴合且具有导电性的成核层，克服了这些限制。凭借其含有缺陷的石墨结构以及化学活性的表面特性——源于有助于铜离子还原的缺陷位点和富电子区域——石墨烯为均匀、连续的铜膜生长提供了均匀的成核位点，从而消除了传统钯/锡（Pd/Sn）活化法中常见的岛状形态，并避免了有毒催化剂的使用。此外，石墨烯的原子级薄度和柔韧性使其能够紧密贴合PCL表面，形成强烈的范德华力，从而增强附着力并防止分层。这种分层PGC结构确保了即使在反复机械变形下也能保持强大的机械完整性。重要的是，石墨烯涂覆过程在温和条件下进行，从而保留了电纺纤维的精细形态，并维持了高性能传感所必需的多孔微结构。作为传感器主要材料的PCL充当热塑性基体，负责热恢复；而涂覆在纤维表面的石墨烯则有助于在恢复过程中稳定界面结构和导电路径。沉积在石墨烯涂层纤维上的铜层主要提供导电性和压力传感功能。由此制备的传感器同时实现了以下独特特性的结合：
(1) 利用多层结构实现宽范围的压力传感；
(2) 通过受损位点的重组恢复传感能力；
(3) 由石墨烯/铜外壳赋予的高温结构稳定性和高传感灵敏度。
这些协同特性使我们的方法与基于纳米复合材料或多层纤维结构的先前设计显著区别开来，这主要是因为石墨烯介导的铜镀层在不牺牲纤维多孔性或柔韧性的前提下，提供了卓越的导电性、附着力和结构完整性。
本研究提出了一种可扩展且实用的策略，用于开发高性能纤维基压力传感器。通过系统性的材料选择和分层结构设计，本研究为下一代传感器平台提供了宝贵的见解，这些平台具备多功能性能属性，适用于可修复、可重复使用的可穿戴设备、柔性传感以及工业应用。
图文导读
图1、Schematic illustration of the layer by layer assembly of the PGC conductive microfiber network pressure sensor. The diagram highlights (1) electrospinning of PCL microfibers and atmospheric plasma activation to introduce surface functional groups, (2) sequential dip coating in graphene dispersion with intermediate drying and ultrasonic cleaning steps, and (3) conformal electroless copper plating to form a continuous metallic shell, followed by stacking onto a PCL support and silver nanowire (AgNW) electrode deposition.
图2、Microscopic characterization of the PGC fiber-based pressure sensor layers. FE-SEM images of (a) as-spun PCL fibers, (b) PCL/graphene fibers before ultrasonication, (c-1, c-2) PCL/graphene fibers after ultrasonication, (d-1) PGC fibers, and (d-2) a magnified view of the electroless Cu-plated fiber surface. Surface morphology of the fiber matrix after various plating durations: (e-1) 3 h, (e-2) 3.5 h, (e-3) 4 h, and (e-4) 4.5 h. This figure illustrates the stepwise morphological evolution of the PGC fibers throughout the fabrication process. The initial PCL fibers display smooth surfaces and high porosity, while the application of graphene introduces nanoscale roughness and enhances surface area. Post-ultrasonication, graphene distribution becomes more uniform and conformal. Subsequent electroless Cu plating forms a metallic shell over the graphene-coated fibers, which becomes increasingly dense and continuous with extended plating durations. These morphological transitions directly influence the sensor’s conductivity, pressure responsiveness, and mechanical robustness, while preserving the overall fibrous architecture after thermal treatment.
图3、Interfacial chemical analysis and Raman characterization of PG and PGC fiber matrix. (a) schematic illustration of the graphene-mediated electroless cu plating process. (b) XPS analysis of pristine PCL fiber. (c, d) High-resolution C 1s and O 1s spectra of pristine PCL fiber. (e) XPS analysis of PG fiber. (f–g) High-resolution C 1s and O 1s spectra of PG fiber. (h) XPS analysis of PGC fiber. (i–k) High resolution C 1s, O 1s, and Cu 2p secptra of PGC fiber. (l) Raman spectrum of PG and PGC fibers, showing the characteristic graphene-related D, G, and 2D bands. XPS analysis results showed that, unlike PG, an electroless copper plating layer was formed on the surface of PGC, and changes in carbon and oxygen-related bonding states were confirmed before and after plating. In the Raman spectrum, specific bands unique to graphene appeared, indicating that the copper layer was sufficiently thin to allow detection of the underlying graphene layer.
图4、Thermally induced recovery behavior and restoration of mechanical and electrical properties in PCL, PG, and PGC fiber mats. Schematic illustrations of (a-1) pristine PCL fiber sheet, (b-1) graphene-coated PCL fiber sheet, and (c-1) PGC fiber sheet. Corresponding optical images of (a) the pristine PCL matrix, (b) the graphene-coated matrix, and (c) the electroless Cu-plated matrix. Thermal treatment of (a-2) PCL fibers at 40°C, (a-3) 60°C, and (a-4) 80°C for 10 min; (b-2) graphene-coated PCL fibers at 60°C, (b-3) 100°C, and (b-4) 140°C for 10 min; (c-2) PGC fibers at 100°C, (c-3) 140°C, and (c-4) 180°C for 10 min. (d) The stress-strain curve of pure PCL, PG, and PGC fiber mats. (e) Stress-strain curves of PCL, PG, and PGC fiber mats after one thermotherapy cycle. (f) A cross-sectional SEM image of the cut PCL fiber mat. (g) A cross-sectional SEM image of the cut PGC fiber mat. (h) Optical microscopy images of PCL and PGC fiber mats before and after thermal repair. (i) SEM image of a cut and repaired PCL fiber mat. (j) A cross-sectional SEM image of a thermally repaired PGC fiber mat. (k) Electrical resistance variations during repeated cut-and-thermal-rapair cycles. (l) Comparison of tensile strength between pristine and repaired PGC fiber matrices. This figure compares the thermally induced recovery behavior of PCL, PG, and PGC fiber mats after damage. Thermal recovery is largely dependent on the thermoplastic properties of PCL. The PGC fiber mat shows the high mechanical strength and electrical performance recovery after repeated cutting and thermal rapair cycles. Optical and SEM images confirm partial structural reconnection of the damaged area after heat treatment.
图5、Sensing performance of the PGC fiber matrix sensor: (a) Current response of a single-layer sensor under incremental pressures from 0.098 to 100 kPa. (b) Influence of the number of PGC layers on current output. (c) Effect of copper plating time on sensor response. (d-1) Current output from a five-layer sensor under five successive press–release cycles. (d-2) Magnified plot showing current variation in the low-pressure region (0.098–40 kPa). (e) Cyclic response of a five-layer sensor under varying pressures from 5 to 200 kPa. (f) Response to the minimum detectable pressure of 0.098 kPa. (g) Current variation at a fixed site through repeated thermal repair cycles. (h) I–V characteristics under pressures of 5, 25, 50, 75, 100, and 200 kPa. (i) Response and recovery times for a 100 kPa load. (j) Long-term durability of the five-layer sensor over 100 000 loading cycles at 100 kPa. This figure illustrates the sensor’s high sensitivity, broad detection range, repeatability, fast response, and exceptional cycling endurance, validating its suitability for practical pressure sensing applications.
图6、Single-pixel load test and crosstalk analysis of a 6 × 6 PGC sensor array. (a-1∼a-3) Images showing a 1 g weight placed on a single pixel in a 6 × 6 PGC sensor array, with the pressed pixel indicated by a red circle. (b-1∼b-3) 3D map of current change when a load is applied to a single pixel within the array. (c) Comparison of the normalized current change of the pressed pixel and the average response of adjacent pixels under applied loads of 1, 5, 10, 15, and 20 g. (d) Crosstalk coefficient according to load, defined as the ratio of the average response of adjacent pixels to the response of the pressed pixel. Since the PGC pressure sensor array maintains local pressure detection while minimizing signal leakage to adjacent pixels, it is suitable for spatially resolved pressure mapping.
小结
本研究表明，经过精心设计的PGC微纤维网络能够克服压力传感器设计中长期存在的权衡问题，同时实现超高灵敏度（> 280 kPa−1）、极其宽广的检测范围（0.098–200 kPa， R² = 0.905），快速机电响应，在100 kPa下超过100 000次循环的长期耐久性，以及在加热至180°C后仍能保持结构和电气功能并稳定运行。这一性能的核心在于大气等离子体活化的石墨烯夹层，它可诱导形成均匀、贴合的无电镀铜壳层，这些铜壳层不仅建立了稳健的电渗通路并强化了纤维界面（抗拉强度高达 13.7 MPa），同时保留了压力依赖性接触调制所需的固有孔隙率。这种由石墨烯介导的无电镀沉积工艺提供了一种不含钯/锡的方法，可在温和条件下实现电纺聚合物纤维上更均匀的铜成核，并有助于减少与传统钯/锡活化相关的非均匀性和预处理复杂性。此外，PCL的低熔点独特地促成了80°C下简便的热辅助修复机制，尽管切口区域未能完全闭合，但可在15分钟内恢复超过95%的电导率和超过90%的机械强度。虽然热恢复是通过熔化 PCL 芯层有意触发的，但 PGC 系统的高温稳定性意味着，在加热过程中，整个纤维形态和导电骨架均由石墨烯-铜壳层维持。
因此，石墨烯/铜层应被视为电学和结构上稳定的层，而非主要的恢复介质。通过优化铜电镀时间（3.5 小时），我们在壳层连续性和孔隙体积之间实现了平衡，从而在多个压力范围内最大限度地提高了线性度和灵敏度。将这些 PGC 垫片集成到 6 × 6 阵列中，证实了其能够对微小载荷（低至 1 克）进行精确的空间映射，且串扰极小，分辨率达 16 像素/cm²，这凸显了该平台的可扩展性及其实际集成的潜力。这些发现突显了分层结构、温和表面活化以及石墨烯介导的界面工程在协调以往相互冲突的传感器要求方面的强大作用。由此开发的PGC平台为下一代可修复、可重复使用的可穿戴接口、柔性压力传感平台、机器人触觉皮肤以及工业环境中的分布式力传感网络提供了多功能的蓝图——在这些应用场景中，高密度、可靠且多功能的压力检测至关重要。未来的研究可探索将其与可持续或可回收的聚合物平台集成，并实现大面积生产以实现经济高效的商业化，从而进一步扩大这一创新材料策略的影响力。
文献：https://doi.org/10.1002/advs.77794
本文来自材料分析与应用，本文观点不代表石墨烯网立场，转载请联系原作者。
