Sakuma Wataru, Yamasaki Shunsuke, Fujisawa Shuji, Kodama Takashi, Shiomi Junichiro, Kanamori Kazuyoshi, Saito Tsuguyuki
Department of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Department of Mechanical Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
ACS Nano. 2021 Jan 26;15(1):1436-1444. doi: 10.1021/acsnano.0c08769. Epub 2021 Jan 6.
Scalability is a common challenge in the structuring of nanoscale particle dispersions, particularly in the drying of these dispersions for producing functional, porous structures such as aerogels. Aerogel production relies on supercritical drying, which exhibits poor scalability. A solution to this scalability limitation is the use of evaporative drying under ambient pressure. However, the evaporative drying of wet gels comprising nanoscale particles is accompanied by a strong capillary force. Therefore, it is challenging to produce evaporative-dried gels or "xerogels" that possess the specific structural profiles of aerogels such as mesoscale pores, high porosity, and high specific surface area (SSA). Herein, we demonstrate a structure of mesoporous xerogels with high porosity (∼80%) and high SSA (>400 m g) achieved by exploiting cellulose nanofibers (CNFs) as the building blocks with tunable interparticle interactions. CNFs are sustainable, wood-derived materials with high strength. In this study, the few-nanometer-wide CNFs bearing carboxy groups were structured into a stable network via ionic inter-CNF interaction. The outline of the resulting xerogels was then tailored into a regular, millimeter-thick, board-like structure. Several characterization techniques highlighted the multifunctionality of the CNF xerogels combining outstanding strength (compression = 170 MPa, σ = 10 MPa; tension = 290 MPa, σ = 8 MPa), moderate light permeability, thermal insulation (0.06-0.07 W m K), and flame self-extinction. As a potential application of the xerogels, daylighting yet insulating, load-bearing wall members can be thus proposed.
可扩展性是纳米级颗粒分散体结构构建中的一个常见挑战，特别是在干燥这些分散体以生产功能性多孔结构（如气凝胶）时。气凝胶的生产依赖于超临界干燥，而超临界干燥的可扩展性较差。解决这种可扩展性限制的一个方法是在常压下使用蒸发干燥。然而，包含纳米级颗粒的湿凝胶的蒸发干燥伴随着强大的毛细作用力。因此，要制备具有气凝胶特定结构特征（如介观孔隙、高孔隙率和高比表面积（SSA））的蒸发干燥凝胶或“干凝胶”具有挑战性。在此，我们展示了一种介孔干凝胶结构，其孔隙率高（约80%）且比表面积大（>400 m²/g），这是通过利用纤维素纳米纤维（CNF）作为具有可调颗粒间相互作用的构建块实现的。CNF是可持续的、源自木材的高强度材料。在本研究中，带有羧基的几纳米宽的CNF通过CNF间的离子相互作用构建成稳定的网络。然后将所得干凝胶的外形加工成规则的、毫米厚的板状结构。几种表征技术突出了CNF干凝胶的多功能性，其兼具出色的强度（压缩强度 = 170 MPa，σ = 10 MPa；拉伸强度 = 290 MPa，σ = 8 MPa）、适度的透光性、隔热性（0.06 - 0.07 W/(m·K)）和火焰自熄性。作为干凝胶的潜在应用，可以提出采光且隔热的承重墙体构件。
