用于自立式三维打印的石墨烯环氧油墨的可逆触变流变特性

摘要：随着三维（3D）打印成为一种新的制造技术，对高性能 3D打印材料的需求也随之增加，以确保其广泛适用于各种承重结构。特别是，材料的触变性能使其在外力作用下流动，而在其他情况下则不流动。据报道，由于材料具有自立和易于加工的特性，因此可以实现快速和高分辨率打印。在这

1成果简介

随着三维（3D）打印成为一种新的制造技术，对高性能 3D打印材料的需求也随之增加，以确保其广泛适用于各种承重结构。特别是，材料的触变性能使其在外力作用下流动，而在其他情况下则不流动。据报道，由于材料具有自立和易于加工的特性，因此可以实现快速和高分辨率打印。在这种情况下，石墨烯纳米片在相邻片之间表现出独特的π-π堆叠相互作用，很可能赋予低粘度油墨自立能力。

本文，韩国成均馆大学In-Kyung Park、Jae-Do Nam等研究人员在《ACS Macro Letters》期刊发表名为“Reversible Thixotropic Rheological Properties of Graphene-Incorporated Epoxy Inks for Self-Standing 3D Printing”的论文，研究开发了一种热固化石墨烯掺杂环氧树脂油墨体系，由于其静态屈服应力高（约1,680 Pa），该体系具有剪切稀化特性和直立能力。

这种复合油墨的粘弹性能和动态屈服应力清楚地表明，原始环氧油墨中不存在从液态到固态的可逆相变。这种触变性复合油墨可实现 10 层叠加的连续长丝打印，且注射的长丝不会扩散。值得注意的是，热固化后的三维打印复合材料结构具有坚固的结构完整性，在堆叠界面上没有焊缝或空隙。我们的研究结果清楚地阐明了油墨系统的加工-结构-性能关系，从而凸显了其广泛的应用潜力。

2图文导读

图1、Schematic illustrations of (a) two-dimensional graphene nanosheets, showing their self-assembly driven by π–π stacking interactions, and (b) continuous filament 3D printing of graphene-incorporated epoxy ink, enabled by reversible thixotropic properties resulting from structural changes in the graphene filler. (c) Digital images of a square spiral structure during the continuous filament 3D printing process, composed of five stacked layers, and (d) stretching of the spiral structure after thermal curing. (e) Raman spectra of pristine graphene and graphite. (f) XPS C 1s and (g) O 1s core-level spectra of pristine graphene.

图2. Rheological properties of the EP and EP/Grph inks with varying graphene content: (a) Representative apparent viscosity and (b) shear stress as functions of shear rate, with solid lines representing the H–B model applied to the rheological data. (c) Viscoelastic behavior represented by storage modulus (G′) and loss modulus (G″) as a function of shear stress. (d) Tan δ (G″/G′) as a function of shear stress, quantifying relative contributions of the elastic and viscous components.

图3. G′ and G″ of the EP/Grph2 composite ink as a function of a three-step strain sequence (low–high–low: 0.01%–50%–0.01%) at a fixed frequency of 1 Hz, demonstrating the ink’s thixotropic behavior. The schematic illustrations show the corresponding dispersion states of graphene nanosheets at each strain step.

图4. (a) η*, G′, and G″ of the EP/Grph2 composite ink as a function of time at 110 °C under isothermal curing conditions, measured with a constant strain of 0.1% and a frequency of 1 Hz. (b) Schematic illustrations depicting the predominant structural upright forces: π–π stacking interactions of graphene nanosheets prior to gelation and the cross-linked epoxy–amine bonds following gelation.

图5. (a) Digital image of sequential 3D line printing using the EP/Grph2 composite ink with a 200 μm nozzle diameter. (b) Height and width of the printed structures as a function of the number of layers. (c) Polished cross-sectional SEM image of the printed structure with 10 layers.

图6. Comparison of the yield stress between the EP/Grph inks and previously reported epoxy composite inks containing carbon-based materials as a function of filler content; a detailed description of the data points is provided in Table S2 of the Supporting Information.

3小结

在本研究中，我们利用加入石墨烯的油墨的流变特性，证明了石墨烯纳米片可以诱发触变性--其特点是可逆相变和很强的直立能力。这种行为可归因于石墨烯网络在 π-π 堆垛相互作用的驱动下的分解和重组。我们清楚地识别了复合油墨的静态和动态屈服应力，并将其与直立能力和简易三维打印性联系起来。根据流变学参数（包括屈服应力和 tan δ）将石墨烯含量优化为 2 wt %，这些参数描述了复合油墨体系的触变性能。此外，化学流变特性表明，即使在凝胶化之前，油墨也具有很强的直立特性，这可能是由于油墨中存在石墨烯网络。总之，这种石墨烯融入墨水展示了连续长丝三维打印的巨大潜力，为设计和制造下一代先进应用提供了广泛的机会。

文献：https://doi.org/10.1021/acsmacrolett.4c00765