研究背景
由于具有各向异性、高强度以及在工程相关领域的实用性强等特点，具有层状结构的纳米复合材料受到了广泛关注。特别是在散热方面，层状结构促进了声子沿径向的良好传输，使平面内的热量快速扩散。与其他热导体相比，这种独特的结构特征在水平散热方面具有压倒性的优势，使其成为微型、薄型和平面设备的完美选择。尽管在提高面内热导率 (K//)以及柔韧性和延展性方面取得了许多突破，但这些因素对于与软电子器件的集成仍然至关重要。首先，几乎所有热导性人造纳米树脂都缺乏足够的粘附性。因此，它们不是自粘，而是依靠银浆或环氧树脂粘合剂作为热界面材料(TIM)来连接器件进行冷却，这不可避免地会导致界面不匹配、K//损失以及在长时间使用后胶水剥落。此外，大多数具有类珍珠层状结构的复合材料都具有很高的硬度，缺乏伸展性和弹性，无法与目前的柔性电子器件(如生物阻抗纹身和电子皮肤)结合。事实上，将具有内在韧性的类珍珠层状与高粘弹性结合在一种材料中似乎是矛盾的，这在自然界中是不存在的。不过，这也为新型类珍珠层状复合材料设计提供了一个机会使其可以规避通常的“硬/软”，从而成为此类应用中极具吸引力的选择。
此外，与隐藏在机器中的传统芯片或晶体管不同，平面电子器件中的电路和显示器通常暴露在人体表面，具有透明性和可视性。因此，智能技术，尤其是柔性设备，对现代热管理系统有很高的要求。除了高热导率、重量轻和可变形等传统特性外，先进的散热材料还具有自愈能力、热响应能力和温度传感能力等多种功能。然而，将这些特性结合到类似珍珠的复合材料中是一项艰巨的任务：内部的分层纹理阻碍了封装制剂的流动性，无法实现外在的自我修复；刚性填料与软聚合物基体的相容性较差，增加了界面热阻，限制了聚合物链的移动，无法实现快速的热响应。为了调解多种成分之间的分子内相互作用，现有研究通常会引入额外的分子，在填料和聚合物基质之间构建 H键网络或共扼体系。然而，在不影响复合材料其他功能的前提下提高导热性仍然是一项挑战。
研究成果
用于软性和平面电子器件的尖端散热器不仅需要高导热性和一定程度的柔韧性，还需要在没有热界面材料的情况下具有出色的自粘性、弹性、任意伸长率以及软性器件和热自修复、热变色等智能特性。具有出色平面散热性能的珍珠层状复合材料是薄型平面电子器件的理想散热器。然而，由于粘弹性(即粘附性和弹性)本身较差，因此无法与当前的柔性器件同时实现自粘附和任意伸长，并且会产生较高的界面热阻。在本文中，陕西科技大学安盟、澳洲迪肯大学刘丹、雷伟伟、四川大学赵长生&新加坡高性能计算研究所张刚教授等人提出了一种柔性热致变色复合膜 (STC)，它具有分层结构、可伸缩性强、平面内导热系数高 (约 30 W m-1K-1)、热接触电阻低(约 12 mm2 KW-1，比银浆低 4-5 倍)、附着力强且可持续(约 4607 J m-2，比环氧树脂浆高 2220 J m-2) 以及自修复效率高等特点。作为一种自粘散热器，它能有效冷却各种软电子器件，比聚酰亚胺外壳的温度降低 20℃。除了自修复功能外，STC 的变色龙般的行为还便于肉眼监测温度，从而实现智能热管理。相关研究以“A Thermochromic, Viscoelastic Nacre‑like Nanocomposite for the Smart Thermal Management of Planar Electronics”为题发表在Nano-Micro Letters期刊上。
研究两点
1. 通过超分子相互作用构建具有波纹状分层结构的粘弹性复合类珍珠层状。
2. 该复合材料表现出出色的自粘性、自愈和耐刮擦机械性能和热性能。
3. 作为集成散热器和TIMs，可对平面柔性电子器件进行“变色龙式“热管理。
图文导读
Fig. 1 a Photos and schematic images of the STC membrane composed of W-SPU, BNNS and TCMs via the VAF strategy and its corresponding application for planar electronics/circuits. The inset displays the flexibility and contact angle of the STC membrane. b Photo of the thermochromic STC inks. c Photos of the STC membranes with thermochromic properties. d Photo of the STC membrane showing the self-adhesive tensile stress. e Photos of STC membranes showing the self-healing property (the cut slices dyed red and blue). f Photos showing the stable col[1]our change of the STC-2 membrane during folding. g Photos showing the outstanding thermochromic performance of the STC membrane self[1]adhered to a soft substrate (top) and cut for self-healing (bottom). h SEM images of the cross-section of the TIM composite membrane.
Fig. 2 a Tensile stress of different STC membranes (I: Photo shows the elongation of STC-2.). b Tensile stresses and self-healing performances for STC-2. c Comparison of tensile stress between STC-2 and W-SPU/BNNS-2. d DMA of W-SPU and STC-2. e XPS of S in the STC after self[1]healing. f Optimized structure simulation and molecular adsorption energy calculation for STC and W-SPU/BNNS. g 2D COS synchronous and asynchronous spectra of STC from 3550 to 3100 cm−1. h 2D COS synchronous and asynchronous spectrum of STC from 1725 to 1500 cm−1. (The warm colour (red) represents positive intensities, while cold colours (blue) represent negative intensities). i SAXS images of STC-2 before and after uniaxial stretching to 300%. j Optical images of the scratch self-healing process of STC-2. k SEM images of the scratch after self-healing of STC-2. The magnified SEM image highlights the surface area of the intact nanosheet network.
Fig. 3 a Photos showing the excellent self-adhesiveness of the STC-2 membrane on various substrates. b Photos showing the repair of substrate by self-adhering STC-2 membrane. c Photos and SAXS images to demonstrate the excellent interfacial adhesiveness after stretching. d SEM image of the interface between the self-adhering STC-2 membrane and the substrate. e Adhesion energy of epoxy paste, STC-2, W-SPU and residues from the 3.rd peeling (I: Photo shows the peeling of STC-2 from the substrate.). f Adhesion force of STC-2 after 1000 cycles of contact and separation (I-III: photos of the test process). g Friction factors of different samples. h ҡ of different samples. i ҡ// of STC-2 after self-healing. j Temperature cyclability of ҡ// from 25° to 70°.
Fig. 4 a Comparison of ҡ and damping loss factor among different materials. b Comparison of ҡ among currently reported polymer composites. c Comparison of Rc and packing pressure of STC-2 with various TIMs.
Fig. 5 Molecular dynamics simulation systems of interfacial thermal resistances where a thin Al film is embedded in a epoxy adhesive (pink colour), b W-SPU/TCM (blue colour denotes W-SPU, yellow colour and mauve colour denote the TCM molecules), c STC-2 (cyan colour denotes the BNNS). d-f Temperature and energy evolutions of the Al thin film and three polymer systems. g Interfacial thermal resistances between the Al thin film and epoxy paste, W-SPU/TCM, STC-2. The overlap of the VPS of two materials at these two interfaces. h VPS of materials in three types of interface systems. i VPS of each component in the STC-2 system.
Fig. 6 Thermal management application for flexible planar electrodes. a Photos of a commercial Kirigami electrode on a PI substrate. b Photos of the Kirigami electrode self-adhered on the STC-2 membrane with excellent flexibility. c Photos of STC-2 membranes with different 3D-printed patterns and electronics (I: polyline-type pattern, II: coil-type pattern, III: embroidery-type pattern, IV: LED arrays). d Photos showing flexibility of various 3D-printed circuits on the STC-2 membrane. e Photos of thermochromic conversion by heat dissipation. f FE simulation (steady model) of the heat diffusion for various 3D-printed circuits on the PI film and STC-2 membrane. g Temperature profile with time. h Cycles of the temperature change of the Kirigami electrode on the STC-2 membrane. i Demonstration of the steady thermal management and thermochromic performances for patterned circuits under stretching and deformations.
总结与展望
这是首次报道了一种具有类珍珠层状结构的热致变色和粘弹性纳米复合材料，它集自粘性和自修复性于一体。由 W-SPU、BNNS 和 TCM 组成的 VAF 衍生膜具有出色的机械和热性能，即优异的拉伸性、相当大的粘弹性和显著的热导性。此外，TCM的引入能与 W-SPU和 BNNS 产生强烈的界面相互作用，因此不仅有助于提高热刺激灵敏度，还能促进强化。更重要的是，STC-2 与基材的抗刮擦能力、超强粘附力和自我修复能力使其能够弥补传统导热类珍珠层状复合材料作为热传播材料的不足。加上高 K//、低 Rc 和 CTE值、良好的可折叠性和热颜色可变性，该类珍珠层状复合材料展示了为不同的软电子器件(如Kirigami电极和 3D 打印电路)实现智能热管理的可能性。因此，预计这一设计理念将为未来一系列先进热应用的人工智能材料做出重大贡献。
文献链接
A Thermochromic, Viscoelastic Nacre‑like Nanocomposite for the Smart Thermal Management of Planar Electronics
https://doi.org/10.1007/s40820-023-01149-8
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