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  近日，廣東工業大學劉曉暄教授高分子光化學團隊在3D打印自修復功能有機硅材料領域取得了階段性進展，研究成果以題為“Self-healing, reprocessing and 3D printing of transparent and hydrolysis resistant silicone elastomers”發表在《Chemical Engineering Journal》。論文的第一作者為廣東工業大學博士生劉珠，通訊作者為劉曉暄教授。

  在加工和使用過程中，有機硅材料會不可避免地遇到微裂紋、開裂等損傷，微裂紋通常很難檢測，持續使用會導致材料的性能下降甚至失效，帶來嚴重的安全隱患。實現快速高效固化的同時，實現自我修復并恢復原有各項性能指標，對提高有機硅材料的使用壽命及安全性，降低更換成本具有重要意義。目前市面工業化有機硅材料還無法實現光固化，這是因為極性光固化基團很難引入聚硅氧烷鏈，制備提純困難，相容性及儲存穩定性差。此外，可逆動態鍵一般也具有強極性較難引入聚硅氧烷鏈，而本征型自修復材料是通過構建可逆動態鍵實現的。為此，目前自修復有機硅彈性體較難同時實現光固化和自修復性能，一般采用熱固化方式且制備出的彈性體不透明、相容性差且抗水解性差。因此，基于優異抗水解性能的自修復透明光固化有機硅材料的研究在3D打印應用領域顯得很有意義。

  劉曉暄教授團隊通過PDMS–SH與端乙烯硅油的光誘導點擊反應及羧基硅油與氨基硅油的熱可逆動態離子交聯構建的可逆/不可逆雜化雙網絡，制備出一種可快速UV固化及優異自修復性的有機硅透明彈性體。并將其應用于3D打印上，打印出具有優異多重自修復性能的有機硅彈性體實體。制備的光-熱雙交聯有機硅彈性體的固化機理及交聯網絡示意圖（圖1）。

圖1 Schematic illustration of photo-thermal dual-curing and crosslinked networks of silicone elastomers.

  制備的雙交聯有機彈性體UV光輻射下，可3 s內凝膠，20 s內巰基-烯初網絡基本交聯完成形成初始強度，且離子交聯網絡不影響巰基-烯光固化網絡的形成，滿足SLA 3D打印的先決條件（圖2）。

圖2 (a) G'' and G'''' during in situ rheological test; (b) real-time infrared spectra (FTIR) of TE–IN samples

  通過變溫紅外（VT-IR）、動態熱機械分析（DMA）及應力松弛行為驗證了彈性體優異的動態可逆性（圖3）。通過彈性體中離子鍵的動態解離和重組，可將有機硅彈性體的斷裂面有效修復，修復效率可達97%以上，且多次修復后，修復效率仍可達92%以上（圖4和圖5）。此外，制備的雙交聯有機硅彈性體具有優異的回收性能，回收后彈性體拉伸強度可恢復90%以上，多次回收后拉伸強度仍可恢復85% 以上。回收后彈性體仍具有優異的自修復性能，多次修復后修復效率仍可達90%以上（圖6）。

圖3 VT-IR spectra of TE–IN10, (a) peak shift as heated from 40 to 120 °C by 10 °C/min, (b) peak shift during cooled from 120 to 40 °C by 10 °C/min. Variation of storage modulus E′ under various temperatures as a function of time, (c) IN samples, (d) TE–IN10 samples. Normalized stress-relaxation curves, (g) TE–IN10 samples under different temperatures and (h) elastomers containing various ionic bonds at 60 °C, (c) Linear fitting of relaxation time (τ) versus temperature according to the Arrhenius'' equation, (d) Stress relaxation activation energy (Ea) of samples with various ionic bonds.

圖4 Illustration of self-healing mechanism.

圖5 (a) Repeated macro-repairing of damaged TE–IN10 samples. Stress-strain curves of virgin and self-healed silicone elastomers, (b) epeatedly healed TE–IN10 samples, (c) TE–IN10, TE–IN20 and TE–IN30 samples healed at 100 °C for 12 h.

圖6 Photographs for the reprocessing of TE–IN10 samples. (b-c) Stress-strain curves of virgin and reprocessed silicone elastomers, (b) repeatedly reprocessed TE–IN10 samples from 80 meshes, (c) self-healing properties of repeated reprocessed TE–IN10 samples.

  制備的雙交聯有機硅彈性體具有優異的透明度。隨著離子網絡含量的增加，可見光透光率仍可達90%以上，多次高溫熱修復及回收后，可見光透光率仍可高達85%以上（圖7）。彈性體具有優異的抗水解性能，即使80 ℃熱水處理48h，彈性體的力學性能、E''和Tg均無明顯降低，此外，經80 ℃熱水處理48h，彈性體試樣仍具有高達90 %以上的修復效率（圖7）。

圖7 Transmittance of (a) silicone elastomers containing various ionic bonds, (b) TE–IN10 samples with different healing times, (c) stress-strain curves and (d) storage modulus E'' and tan δ of TE–IN10 samples after hydro-thermally treated.

  有機硅彈性體配方通過Form 2桌面式SLA 3D打印機，可打印出表面光滑和輪廓清晰的彈性體實體（如“GDUT”校名縮寫，“齒輪”和“幸運星”），且有機顏料加入后不會影響固化速率。此外，3D打印出彈性體實體具有優異的自修復性能，多次修復后，自修復效率仍可達99%以上。表明3D打印層狀堆疊不影響離子網絡的分布及可逆解離—重組過程。

圖8 (a) Schematic of SLA-based 3D printing. (b) 3D printed various geometries from TE–IN10 formula with different pigments, “GDUT” with 1.0 wt% RP–355, “Toothed Gears” in turn with 0.05 wt% BP–825, 0.05 wt% RP–355, and 1.0 wt.% BP–825, “Ascendant” with 0.05 wt% RP–355. (c) Photographs of self-healing 3D printed “Ascendant”. (d) Stress-strain curves of repeatedly self-healed 3D printed samples after 100 °C for 12 h.

  因此，通過巰基-烯快速光聚合及熱可逆離子交聯的光—熱雙交聯方式，成功地制備出優異透明度及抗水解性能的自修復可回收3D打印有機硅彈性體。對長時間打印出的復雜結構的彈性體功能件具有重要意義，節能環保，延長使用壽命、降低成本。為基于可逆動態離子締合誘導的快速固化自修復有機硅材料提供一種可行的方案。

  論文鏈接：https://doi.org/10.1016/j.cej.2020.124142

  作者所在課題組的主研方向為高分子光化學，包括巰基-烯光點擊化學、3D打印彈性體、3D打印自修復材料和多功能光引發劑，相關成果發表在《Progress in Polymer Science》、《Journal of Materials Chemistry C》《Polymer Chemistry》《Langmuir》、《Journal of Photochemistry & Photobiology A: Chemistry》、《ChemPhotoChem》（Angewandte Chemie International Edition, Chemistry - ChemPhotoChem）和《Progress in Organic Coatings》等該領域TOP國際主流期刊上。

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https://doi.org/10.1016/j.porgcoat. 2019.105372