由於具備高比表面積、可調整的孔洞尺寸、和孔洞內部聯通性的優勢，孔洞材料在近年來獲得許多的關注，然而在工業製程上，模具成型的高成本使孔洞材料非常困難去客製化複雜的結構。近期出現名為積層製造的革新技術，主要利用數位方式控制物件的層層堆疊而具備較高的設計自由度，目前已知有些文章利用高內相乳液作為墨水來3D列印出開放性的多孔材料，但是脆弱的機械性質和較大尺度的孔洞會使其應用受限。
　　在本篇研究中，我們結合中内相乳液和高剪切能量來形成細乳液，並以其作為列印墨水來列印具備尺度低於微米等級的多孔高分子材料。由於高剪切力作用，分散相液滴尺寸會下降並發生膠化作用，此時形成的細乳膠會具備剪切稀化的行為且其彈性模量能透過調整分散相體積占比來得到適當的數值。高剪切能量同時也使分散相液滴間的距離下降，因此在連續相經過光聚合後，我們能獲得尺度在微米等級以下且內部孔洞連通的多孔高分子材料。我們同時也對此多孔高分子材料進行性質分析，由高數值的凝膠分數能夠知道此材料具備高交聯比例與純度；機械性質和熱性質各自受到分散相體積占比和交聯劑的用量所影響。
　　基於流變、機械、和熱性質分析結果，我們最終選擇的配方為分散相占比60%和7.5%的交聯劑用量的細乳膠並利用直接墨水書寫式列印來列印具尺度低於微米等級的多孔高分子材料。網狀與蜂巢狀結構的列印顯示此墨水具備足夠的彈性模量和降伏應力來達成高精度和高解析度的列印；透過聚丙烯酸十八酯的結晶/融化行為，我們能利用直接墨水書寫式列印和熱引發塑形製造中空螺旋管和莫比烏斯環；由於機械性質的改善，使用此方式製備的機械手展現舉起重物的能力。本研究為製備具尺度微米等級以下孔洞和較佳機械強度的高分子材料創造一個新的可能性，那就是以細乳膠作為3D列印墨水在形狀記憶的輔助下達到客製化複雜結構的效果。

Porous monoliths have received various attentions in recent years due to their high specific surface area, tunable pore size, and interconnectivity between pores. For industrial methods of preparing porous materials, the high cost of the traditional molding process made it difficult to customize complex structures. Recently, additive manufacturing was an innovative technique that achieves high design freedom by depositing materials layer-by-layer with digital control. Some works have fabricated open-cellular porous materials by 3D printing with the ink of high internal phase emulsions (HIPE). However, the application of the monoliths from HIPE is limited by their poor mechanical performance and the large pore size.
　　In this work, we applied high shear energy to medium internal phase emulsion (MIPE) to prepare jammed miniemulsion inks that provide 3D printable porous polymeric monoliths with sub-micrometer pores. The jammed miniemulsion ink showed shear-thinning behavior and appropriate elastic modulus that could be tailored by the volume fraction of dispersed phase. After the photopolymerization of the continuous phase, we could acquire the interconnected sub-micro porous monoliths. The high gel fraction of the porous monoliths confirmed the successful photo-crosslinking. The mechanical and thermal properties of the porous monoliths were affected by the volume fraction of dispersed phase and amount of crosslinker, respectively.
　　On the basis of the rheological, mechanical, and thermal properties, we finally chose the jammed MIPE ink with 60 vol% dispersed phase and with 7.5% crosslinker to print the sub-micrometer porous monoliths with interconnected structures by direct ink writing (DIW). The mesh and honeycomb structure indicated the ink could achieve highly precise printing and high resolution because of its high elastic modulus and yield stress. A hollow helical tubing and a Mӧbius band were manufactured by DIW and the thermally induced shape-changing enabled by the crystallization/melting of poly(stearyl acrylate). The robot gripper fabricated by this method showed the ability to hold heavy objects because of the improvement of mechanical strength. This study created the new possibility for fabricating the sub-micrometer porous polymeric monoliths that could be customized into complex structures with high mechanical performance.

1. Zhang, N.; Zhong, S.; Chen, T.; Zhou, Y.; Jiang, W., Emulsion-derived hierarchically porous polystyrene solid foam for oil removal from aqueous environment. RSC Advances 2017, 7 (37), 22946-22953.
2. Ambekar R. S.; Kandasubramanian B., Progress in the advancement of porous biopolymer scaffold: tissue engineering application. Industrial & Engineering Chemistry Research 2019, 58 (16), 6163-6194.
3. Svec, F., Porous polymer monoliths: amazingly wide variety of techniques enabling their preparation. Journal of Chromatography A 2010, 1217 (6), 902-24.
4. Rouquerol, J.; Avnir D.; Fairbridge C. W.; Everett D. H.; Haynes J. H.; Pernicone N.; Ramsay J. D. F.; Sing K. S. W.; Unger K. K., Recommendations for the characterization of porous solids. Pure and Applied Chemistry 1994, 66 (8), 1739-1758.
5. Thompson, B. R.; Horozov, T. S.; Stoyanov, S. D.; Paunov, V. N., Hierarchically structured composites and porous materials from soft templates: fabrication and applications. Journal of Materials Chemistry A 2019, 7 (14), 8030-8049.
6. Yang, X. Y.; Chen, L. H.; Li, Y.; Rooke, J. C.; Sanchez, C.; Su, B. L., Hierarchically porous materials: synthesis strategies and structure design. Chemical Society Reviews 2017, 46 (2), 481-558.
7. Wegst, U. G.; Bai, H.; Saiz, E.; Tomsia, A. P.; Ritchie, R. O., Bioinspired structural materials. Nature Materials 2015, 14 (1), 23-36.
8. Yu, H.; Fisher, A.; Cheng, D.; Cao, D., Cu,N-codoped hierarchical porous carbons as electrocatalysts for oxygen reduction reaction. ACS Applied Materials & Interfaces 2016, 8 (33), 21431-9.
9. Nagarajan, R., Molecular theory for mixed micelles. Langmuir 1985, 1, 331-341.
10. Su, B. L.; Sanchez, C.;Yang, X. Y., Hierarchically structured porous materials by dually micellar templating approach. 2012; p 41-53.
11. Sylvain D.; Saiz E.; Antoni P. T., Ice-templated porous alumina structures. Acta materialia 2007, 55 (6), 1965-1974.
12. Feinle, A.; Elsaesser, M. S.; Husing, N., Sol-gel synthesis of monolithic materials with hierarchical porosity. Chemical Society Reviews 2016, 45 (12), 3377-99.
13. Hüsing N.; Schubert U., Aerogels–Airy Materials: Chemistry, Structure, and Properties. Angewandte Chemie International Edition 1998, 37, 22-45.
14. Style, R. W.; Tutika, R.; Kim, J. Y.; Bartlett, M. D., Solid–liquid composites for soft multifunctional materials. Advanced Functional Materials 2020, 31 (1).
15. Goodarzi, F.; Zendehboudi, S., A comprehensive review on emulsions and emulsion stability in chemical and energy industries. The Canadian Journal of Chemical Engineering 2018, 97 (1), 281-309.
16. Aldemir Dikici, B.; Claeyssens, F., Basic principles of emulsion templating and its use as an emerging manufacturing method of tissue engineering scaffolds. In Frontiers in Bioengineering and Biotechnology, 2020/09/10 ed.; 2020; Vol. 8, p 875.
17. McClements, D. J.; Jafari, S. M., Improving emulsion formation, stability and performance using mixed emulsifiers: a review. Advances in Colloid and Interface Science 2018, 251, 55-79.
18. Zhang, H.; Cooper, A. I., Synthesis and applications of emulsion-templated porous materials. Soft Matter 2005, 1 (2), 107-113.
19. Moon, S.; Kim, J. Q.; Kim, B. Q.; Chae, J.; Choi, S. Q., Processable composites with extreme material capacities: toward designer high internal phase emulsions and foams. Chemistry of Materials 2020, 32 (11), 4838-4854.
20. Lissant, K. J., The geometry of high-internal-phase-ratio emulsions. Journal of Colloid and Interface Science 1966, 22, 462-468.
21. Pal, R., Yield stress and viscoelastic properties of high internal phase ratio emulsions. Colloid and Polymer Science 1999, 277, 583-588.
22. Princen H. M.; Kiss A. D., Rheology of foams and highly concentrated emulsions: III. static shear modulus. Journal of Colloid and Interface Science 1985, 112 (2), 427-437.
23. Zhang, T.; Sanguramath, R. A.; Israel, S.; Silverstein, M. S., Emulsion templating: porous polymers and beyond. Macromolecules 2019, 52 (15), 5445-5479.
24. Luo, Y.; Wang, A. N.; Gao, X., Pushing the mechanical strength of polyHIPEs up to the theoretical limit through living radical polymerization. Soft Matter 2012, 8 (6), 1824-1830.
25. Ramsden W., Separation of solids in the surface-layers of solutions and ‘suspensions’ (observations on surface-membranes, bubbles, emulsions, and mechanical coagulation).—Preliminary account. Proceedings of the Royal Society of London 1904, 72, 156-164.
26. Spencer Umfreville Pickering, M. A., F.R.S., CXCVI.—emulsions. Journal of Chemical Society, Transactions 1907, 91, 2001-2021.
27. Chevalier, Y.; Bolzinger, M. A., Emulsions stabilized with solid nanoparticles: Pickering emulsions. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2013, 439, 23-34.
28. Glasing, J.; Jessop, P. G.; Champagne, P.; Cunningham, M. F., Graft-modified cellulose nanocrystals as CO2-switchable Pickering emulsifiers. Polymer Chemistry 2018, 9 (28), 3864-3872.
29. Jiang, H.; Sheng, Y.; Ngai, T., Pickering emulsions: versatility of colloidal particles and recent applications. Curr. Opin. Colloid Interface Sci. 2020, 49, 1-15.
30. Woodward, R. T.; Markoulidis, F.; De Luca, F.; Anthony, D. B.; Malko, D.; McDonald, T. O.; Shaffer, M. S. P.; Bismarck, A., Carbon foams from emulsion-templated reduced graphene oxide polymer composites: electrodes for supercapacitor devices. Journal of Materials Chemistry A 2018, 6 (4), 1840-1849.
31. Yang, T.; Hu, Y.; Wang, C.; Binks, B. P., Fabrication of hierarchical macroporous biocompatible scaffolds by combining Pickering high internal phase emulsion templates with three-dimensional printing. ACS Applied Materials & Interfaces 2017, 9 (27), 22950-22958.
32. Joseph Schork, F.; Luo, Y.; Smulders W.; Russum J. P.; Butté A.; Fontenot K., Miniemulsion polymerization. Advances in Polymer Science 2005, 175.
33. Fukui, Y.; Fujino, R.; Sugaya, Y.; Fujimoto, K., Creation of porous polymeric membranes by accumulation of water nanodroplets in a miniemulsion system. Polymer Journal 2020, 52 (9), 1077-1083.
34. Blin, J. L.; Stébé, M. J.; Lebeau, B., Hybrid/porous materials obtained from nano-emulsions. Curr. Opin. Colloid Interface Sci. 2016, 25, 75-82.
35. Crespy, D.; Landfester, K., Miniemulsion polymerization as a versatile tool for the synthesis of functionalized polymers. Beilstein Journal of Organic Chemistry 2010, 6, 1132-48.
36. Luo, Y.; Wang, A. N.; Gao, X., Miniemulsion template polymerization to prepare a sub-micrometer porous polymeric monolith with an inter-connected structure and very high mechanical strength. Soft Matter 2012, 8 (29).
37. González-Henríquez, C. M.; Sarabia-Vallejos, M. A.; Rodriguez-Hernandez, J., Polymers for additive manufacturing and 4D-printing: materials, methodologies, and biomedical applications. Progress in Polymer Science 2019, 94, 57-116.
38. Wang, X.; Jiang, M.; Zhou, Z.; Gou, J.; Hui, D., 3D printing of polymer matrix composites: a review and prospective. Composites Part B: Engineering 2017, 110, 442-458.
39. Sood, A. K.; Ohdar, R. K.; Mahapatra, S. S., Parametric appraisal of mechanical property of fused deposition modelling processed parts. Materials and Design 2010, 31 (1), 287-295.
40. Truby, R. L.; Lewis, J. A., Printing soft matter in three dimensions. Nature review 2016, 540 (7633), 371-378.
41. Kim, G. B.; Lee, S.; Kim, H.; Yang, D. H.; Kim, Y. H.; Kyung, Y. S.; Kim, C. S.; Choi, S. H.; Kim, B. J.; Ha, H.; Kwon, S. U.; Kim, N., Three-dimensional printing: basic principles and applications in medicine and radiology. Korean Journal of Radiology 2016, 17 (2), 182-97.
42. Mu, Q.; Wang, L.; Dunn, C. K.; Kuang, X.; Duan, F.; Zhang, Z.; Qi, H. J.; Wang, T., Digital light processing 3D printing of conductive complex structures. Additive Manufacturing 2017, 18, 74-83.
43. Wan, X.; Luo, L.; Liu, Y.; Leng, J., Direct ink writing based 4D printing of materials and their applications. Advanced Science 2020, 7 (16), 2001000.
44. Solís Pinargote, N. W.; Smirnov, A.; Peretyagin, N.; Seleznev, A.; Peretyagin, P., Direct ink writing technology (3D printing) of graphene-based ceramic nanocomposites: a review. Nanomaterials 2020, 10 (7), 1300.
45. Chen, Y.; Li, W.; Zhang, C.; Wu, Z.; Liu, J., Recent developments of biomaterials for additive manufacturing of bone scaffolds. Advanced Healthcare Materials 2020, e2000724.
46. Liu, J.; Wang, P.; He, Y.; Liu, K.; Miao, R.; Fang, Y., Polymerizable nonconventional gel emulsions and their utilization in the template preparation of low-density, high-strength polymeric monoliths and 3D printing. Macromolecules 2019, 52 (6), 2456-2463.
47. Minas, C.; Carnelli, D.; Tervoort, E.; Studart, A. R., 3D Printing of Emulsions and Foams into Hierarchical Porous Ceramics. Advanced Materials 2016, 28 (45), 9993-9999.
48. Lewis, J. A., Direct ink writing of 3D functional materials. Advanced Functional Materials 2006, 16 (17), 2193-2204.
49. Lai, C. W.; Yu, S. S., 3D printable strain sensors from deep eutectic solvents and cellulose nanocrystals. ACS Applied Materials & Interfaces 2020, 12 (30), 34235-34244.
50. Hu, Y.; Wang, J.; Li, X.; Hu, X.; Zhou, W.; Dong, X.; Wang, C.; Yang, Z.; Binks, B. P., Facile preparation of bioactive nanoparticle/poly(epsilon-caprolactone) hierarchical porous scaffolds via 3D printing of high internal phase Pickering emulsions. Journal of Colloid and Interface Science 2019, 545, 104-115.
51. Ordian G.; Bernstein B. S., Memory effects in irradiated polyethylene. Journal of Applied Polymer Science 1964, 8, 1853-1867.
52. Xia, Y.; He, Y.; Zhang, F.; Liu, Y.; Leng, J., A review of shape memory polymers and composites: mechanisms, materials, and applications. Advanced Materials 2020, 33 (6).
53. Zhang, F.; Xia, Y.; Liu, Y.; Leng, J., Nano/microstructures of shape memory polymers: from materials to applications. Nanoscale Horizons 2020, 5 (8), 1155-1173.
54. Lendlein, A.; Gould, O. E. C., Reprogrammable recovery and actuation behaviour of shape-memory polymers. Nature Reviews Materials 2019, 4 (2), 116-133.
55. Hearon, K.; Singhal, P.; Horn, J.; Small, W. t.; Olsovsky, C.; Maitland, K. C.; Wilson, T. S.; Maitland, D. J., Porous shape memory polymers. Polymer Reviews 2013, 53 (1), 41-75.
56. Hasan, S. M.; Nash, L. D.; Maitland, D. J., Porous shape memory polymers: Design and applications. Journal of Polymer Science Part B: Polymer Physics 2016, 54 (14), 1300-1318.
57. Nejad, H. B.; Baker, R. M.; Mather, P. T., Preparation and characterization of triple shape memory composite foams. Soft Matter 2014, 10 (40), 8066-74.
58. Hou, Y.; Fang, G.; Jiang, Y.; Song, H.; Zhang, Y.; Zhao, Q., Emulsion lyophilization as a facile pathway to fabricate stretchable polymer foams enabling multishape memory effect and clip application. ACS Applied Materials & Interfaces 2019, 11 (35), 32423-32430.
59. Livshin, S.; Silverstein, M. S., Cross-linker flexibility in porous crystalline polymers synthesized from long side-chain monomers through emulsion templating. Soft Matter 2008, 4 (8), 1630-1638.
60. Kagami Y., Kung J. P., Osada Y., Shape memory behaviors of crosslinked copolymers containing stearyl acrylate. Macromolecular Rapid Communications 1996, 17, 539-543.
61. Gurevitch, I.; Silverstein, M. S., Shape memory polymer foams from emulsion templating. Soft Matter 2012, 8 (40).