高濃度奈米碳管（Carbon nanotubes, CNTs）的3D列印不容易達成，因為這面臨著各種挑戰。首先，CNTs 在化學上和物理上是非常穩定的，無法熔化和聚合。其次，CNTs 在大多數溶劑中往往會聚集，導致難以製備高含量的CNTs 配方。此外，添加流變改性劑或分散劑可能會降低整體的導電性。迄今為止，已有一些研究報導了製備 3D 可列印的高濃度 CNTs 的方法。然而，這些方法僅限於微米級結構的3D列印。
在這項研究中，我們開發了一種環境友善且簡易的方法，利用直接書寫式(Direct ink writing, DIW)技術製備具有形狀重塑能力和焦耳加熱行為的CNTs 奈米複合材料。我們的可列印墨水由高濃度 CNTs 在聚乙烯醇（Polyvinyl alcohol, PVA）水溶液中分散而成，其中含有聚乙烯吡咯烷酮（Polyvinyl pyrrolidone, PVP）來協助 CNTs穩定分散在此系統中。墨水的流變性質通過CNTs和PVP的含量來調節。列印的物體經過冷凍-解凍(Freeze-thaw)過程形成水凝膠。該水凝膠的形成是由 PVA 的結晶所引起的。PVA 的物理交聯網絡作為支撐列印物體的聚合物支架，而CNTs嵌在聚合物網絡中。隨後，將奈米複合水凝膠浸泡在由氯化膽鹼和甘油所組成的深共熔溶劑（Deep eutectic solvent, DES）中。此步驟用DES取代水凝膠中的水。我們利用這奈米複合 DES 凝膠的優異機械性能，展示了其形狀重塑能力。這種能力使我們能夠實現一些很難單靠 DIW 來實現的更複雜幾何結構。最後，樣品在乙醇中進行溶劑交換，隨後進行乾燥，以固定其形狀並提高整體的 CNTs 含量。最終的產物在優化配方下，CNTs 含量超過 45 wt%，並具有 33.94 S/m的高電導率。此外，這奈米複合材料也表現出顯著的焦耳加熱表現。當其連接到 5 V電壓的 電路時，它可以在 4分鐘內達到 100 oC。
另外，我們通過將樣品選擇性部分浸泡在乙醇中的方式成功製造了一個多材料結構。該複合材料在其不同部位具有不同的物理特性，例如機械、導電和焦耳加熱特性。這成功地示範了一種新穎的方式來製作可客制化的多樣性質的材料。

The 3D printing of high-concentration carbon nanotubes (CNTs) presents various challenges. First, CNTs are chemically and physically stable, making them unable to be melted and polymerized. Second, CNTs tend to aggregate in most solvents, resulting in difficulty in formulating high-content CNTs. Additionally, adding rheological modifiers or dispersants can compromise the overall conductivity. To date, there are only a few studies that 3D print structures with high concentrations of CNTs. Moreover, these approaches are limited to 3D printing of micro-scale structures.
In this work, we developed an ecofriendly, green, and efficient approach to fabricate CNTs nanocomposite with shape reconfiguration ability and Joule heating behavior, incorporating the direct ink writing (DIW) technique. Our 3D printable ink consisted of a high concentration of CNTs stabilized by polyvinylpyrrolidone (PVP) in an aqueous polyvinyl alcohol (PVA) solution. The rheology of the ink was tuned by the amounts of CNTs and PVP. The printed object underwent the freeze-thaw process to form hydrogel induced by the crystallization of PVA. The physically crosslinked network of PVA served as the polymer scaffold to support the printed object, with the CNTs embedded within the polymer network. Subsequently, the nanocomposite hydrogel was immersed in a deep eutectic solvent (DES) bath consisting of choline chloride and glycerol. This step replaced the water within the hydrogel with DES. We utilized the promising mechanical properties of the nanocomposite DES gel to demonstrate its shape reconfiguration ability. This capability allowed us to achieve more complex geometries that would be challenging to accomplish solely with DIW. Finally, the sample underwent solvent exchange with ethanol, followed by drying, to retain the shape and increase the CNTs content. The final object, formulated with an optimized recipe, contained CNTs at a concentration exceeding 40 wt% and demonstrated a high electrical conductivity of 33.94 S/m. Moreover, the nanocomposite exhibited remarkable Joule heating performance, that it could reach 100 oC in 4 mins when connected to the circuit with an applied voltage of 5 V.
Additionally, we successfully fabricated a multi-material structure through selective immersion in an ethanol bath. The multi-material possessed distinct physical properties, such as mechanical, electrical conductivity, and Joule heating properties, in different parts of it. This achievement allowed us to 3D print structures with distinct properties.

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