Huang Yintong, Kasuga Takaaki, Nogi Masaya, Koga Hirotaka
SANKEN (The Institute of Scientific and Industrial Research), Osaka University 8-1 Mihogaoka Ibaraki Osaka 567-0047 Japan
RSC Adv. 2023 Jul 17;13(31):21494-21501. doi: 10.1039/d3ra03840h. eCollection 2023 Jul 12.
Optically transparent materials that are air permeable have potentially numerous applications, including in wearable devices. From the perspective of sustainable development, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers with widths of 3-4 nm have attracted considerable attention as starting materials for the preparation of clearly transparent nanofiber paper (denoted as conventional nanopaper). However, conventional nanopaper that is prepared from a water dispersion of TEMPO-oxidized cellulose nanofibers by direct drying exhibits poor air permeability owing to its densely packed layered structure. In this study, we prepared a clearly transparent and air-permeable nanopaper by applying filtration-based solvent exchange from high-surface-tension water to low-surface-tension ethanol and hexane, followed by drying under continuous vacuum filtration. The resulting hexane-exchanged nanopaper had a porous structure with individually dispersed and thin nanofiber networks and interlayer pore spaces. Owing to the tailored porous structures, the hexane-exchanged nanopaper provides similar clear transparency (total light transmittance and haze at 600 nm: 92.9% and 7.22%, respectively) and 10 times higher air permeability (7.8 × 10 mL μm m day kPa) compared to the conventional nanopaper. This study will facilitate the development of clearly transparent and air-permeable nanopapers to extend their functional applications.
具有透气性能的光学透明材料具有潜在的众多应用，包括在可穿戴设备中。从可持续发展的角度来看，宽度为3-4纳米的2,2,6,6-四甲基哌啶-1-氧基（TEMPO）氧化纤维素纳米纤维作为制备透明纳米纤维纸（称为传统纳米纸）的起始材料引起了相当大的关注。然而，通过直接干燥由TEMPO氧化纤维素纳米纤维的水分散体制备的传统纳米纸由于其密集堆积的层状结构而表现出较差的透气性。在本研究中，我们通过应用基于过滤的溶剂交换，从高表面张力的水到低表面张力的乙醇和己烷，然后在连续真空过滤下干燥，制备了一种透明且透气的纳米纸。所得的己烷交换纳米纸具有多孔结构，其中纳米纤维网络单独分散且较薄，并且存在层间孔隙空间。由于定制的多孔结构，与传统纳米纸相比，己烷交换纳米纸具有相似的透明透明度（600nm处的总透光率和雾度分别为92.9%和7.22%）和高10倍的透气性（7.8×10 mL μm m day kPa）。这项研究将促进透明且透气纳米纸的开发，以扩展其功能应用。
