College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University , Chengdu 610065, China.
Guangdong Shengyi Technology Limited Corporation , Dongguan 523039, China.
ACS Appl Mater Interfaces. 2017 Sep 6;9(35):30035-30045. doi: 10.1021/acsami.7b08214. Epub 2017 Aug 24.
Boron nitride nanosheet (BNNS) films receive wide attention in both academia and industry because of their high thermal conductivity (TC) and good electrical insulation capability. However, the brittleness and low strength of the BNNS film largely limit its application. Herein, functionalized BNNSs (f-BNNSs) with a well-maintained in-plane crystalline structure were first prepared utilizing urea in the aqueous solution via ball-milling for the purpose of improving their stability in water and enhancing the interaction with the polymer matrix. Then, a biodegradable and highly thermally conductive film with an orderly oriented structure based on cellulose nanofibers (CNFs) and f-BNNSs was prepared just by simple vacuum-assisted filtration. The modification of the BNNS and the introduction of the CNF result in a better orientation of the f-BNNS, sufficient connection between f-BNNS themselves, and strong interaction between f-BNNS and CNF, which not only make the prepared composite film strong and tough but also possess higher in-plane TC. An increase of 70% in-plane TC, 63.2% tensile strength, and 77.8% elongation could be achieved for CNF/f-BNNS films, compared with that for CNF/BNNS films at the filler content of 70%. Although at such a high f-BNNS content, this composite film can be bended and folded. It is even more interesting to find that the in-plane TC could be greatly enhanced with the decrease of the thickness of the film, and a value of 30.25 W/m K can be achieved at the thickness of ∼30 μm for the film containing 70 wt % f-BNNS. We believe that this highly thermally conductive film with good strength and toughness could have potential applications in next-generation highly powerful and collapsible electronic devices.
氮化硼纳米片（BNNS）由于其高热导率（TC）和良好的电绝缘性能，在学术界和工业界受到广泛关注。然而，BNNS 薄膜的脆性和强度低在很大程度上限制了其应用。在此，我们首次利用尿素在水溶液中通过球磨制备了具有良好面内结晶结构的功能化 BNNS（f-BNNS），以提高其在水中的稳定性并增强与聚合物基体的相互作用。然后，通过简单的真空辅助过滤，制备了一种基于纤维素纳米纤维（CNF）和 f-BNNS 的具有有序取向结构的可生物降解且高热导率的薄膜。BNNS 的修饰和 CNF 的引入导致 f-BNNS 更好的取向、f-BNNS 之间的充分连接以及 f-BNNS 与 CNF 之间的强相互作用，这不仅使制备的复合膜具有高强度和韧性，而且具有更高的面内热导率。与 CNF/BNNS 薄膜相比，在填料含量为 70%时，CNF/f-BNNS 薄膜的面内热导率提高了 70%，拉伸强度提高了 63.2%，伸长率提高了 77.8%。尽管在如此高的 f-BNNS 含量下，这种复合膜可以弯曲和折叠。更有趣的是，随着薄膜厚度的减小，面内热导率可以大大提高，当薄膜中含有 70wt%f-BNNS 时，厚度约为 30μm 时，面内热导率可达到 30.25W/mK。我们相信，这种具有良好强度和韧性的高热导率薄膜在下一代高功率和可折叠电子设备中具有潜在的应用前景。
