Arapov Kirill, Abbel Robert, de With Gijsbertus, Friedrich Heiner
Laboratory of Materials and Interface Chemistry, Dept. of Chemical Engineering and Chemistry, Eindhoven University of Technology, Den Dolech 2, 5612AZ, Eindhoven, The Netherlands.
Faraday Discuss. 2014;173:323-36. doi: 10.1039/c4fd00067f.
The inkjet printing of graphene is a cost-effective, and versatile deposition technique for both transparent and non-transparent conductive films. Printing graphene on paper is aimed at low-end, high-volume applications, i.e., in electromagnetic shielding, photovoltaics or, e.g., as a replacement for the metal in antennas of radio-frequency identification devices, thereby improving their recyclability and biocompatibility. Here, we present a comparison of two graphene inks, one prepared by the solubilization of expanded graphite in the presence of a surface active polymer, and the other by covalent graphene functionalization followed by redispersion in a solvent but without a surfactant. The non-oxidative functionalization of graphite in the form of a donor-type graphite intercalation compound was carried out by a Birch-type alkylation, where graphene can be viewed as a macrocarbanion. To increase the amount of functionalization we employed a graphite precursor with a high edge to bulk carbon ratio, thus, allowing us to achieve up to six weight percent of functional groups. The functionalized graphene can be readily dispersed at concentrations of up to 3 mg ml(-1) in non-toxic organic solvents, and is colloidally stable for more than 2 months. The two inks are readily inkjet printable with good to satisfactory spreading. Analysis of the sheet resistance of the deposited films demonstrated that the inks based on expanded graphite outperform the functionalized graphene inks, possibly due to the significantly larger graphene sheet size in the former, which minimizes the number of sheet-to-sheet contacts along the conductive path. We found that the sheet resistance of printed large-area films decreased with an increase of the number of printed layers. Conductivity levels reached approximately 1-2 kΩ □(-1) for 15 printing passes, which roughly equals a film thickness of 800 nm for expanded graphite based inks, and 2 MΩ □(-1) for 15 printing passes of functionalized graphene, having a film thickness of 900 nm. Our results show that ink preparation and inkjet printing of graphene-based inks is simple and efficient, and therefore has a high potential to compete with other conductive ink formulations for large-area printing of conductive films.
石墨烯的喷墨打印是一种经济高效且通用的沉积技术，可用于制备透明和非透明导电薄膜。在纸张上打印石墨烯旨在用于低端、大批量应用，例如电磁屏蔽、光伏领域，或者作为射频识别设备天线中金属的替代品，从而提高其可回收性和生物相容性。在此，我们对两种石墨烯墨水进行了比较，一种是通过在表面活性聚合物存在下使膨胀石墨溶解制备而成，另一种是通过共价石墨烯功能化，随后在无表面活性剂的溶剂中重新分散制备而成。以供体型石墨插层化合物形式存在的石墨的非氧化功能化是通过Birch型烷基化进行的，其中石墨烯可被视为一种大碳负离子。为了增加功能化的量，我们使用了具有高边缘与体相碳比的石墨前驱体，因此能够实现高达6重量百分比的官能团。功能化石墨烯能够以高达3 mg ml(-1)的浓度轻松分散在无毒有机溶剂中，并且在胶体状态下稳定超过2个月。这两种墨水都易于进行喷墨打印，铺展性良好至令人满意。对沉积薄膜的表面电阻分析表明，基于膨胀石墨的墨水在性能上优于功能化石墨烯墨水，这可能是由于前者中石墨烯片尺寸明显更大，从而使导电路径上片与片之间的接触数量降至最低。我们发现，印刷大面积薄膜的表面电阻随着印刷层数的增加而降低。对于基于膨胀石墨的墨水，15次印刷道次后的电导率水平达到约1 - 2 kΩ □(-1)，这大致相当于薄膜厚度为800 nm；对于功能化石墨烯的15次印刷道次，电导率为2 MΩ □(-1)，薄膜厚度为900 nm。我们的结果表明，基于石墨烯的墨水的制备和喷墨打印简单高效，因此在与其他导电墨水配方竞争用于大面积导电薄膜印刷方面具有很大潜力。
