Acetylation of optically transparent cellulose nanopaper for high thermal and moisture resistance in a flexible device substrate

This is the Accepted Manuscript version of an article accepted for publication in Flex. Print. Electron.. IOP Publishing Ltd are not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/2058-8585/aa60f4

Checkered films of multiaxis oriented nanocelluloses by liquid-phase three-dimensional patterning

Uetani, K.; Koga, H.; Nogi, M. Checkered Films of Multiaxis Oriented Nanocelluloses by Liquid-Phase Three-Dimensional Patterning. Nanomaterials 2020, 10, 958. https://doi.org/10.3390/nano10050958

Hazy Transparent Cellulose Nanopaper

Hsieh, MC., Koga, H., Suganuma, K. et al. Hazy Transparent Cellulose Nanopaper. Sci Rep 7, 41590 (2017). https://doi.org/10.1038/srep41590

Wirelessly Powered Sensing Fertilizer for Precision and Sustainable Agriculture

Sensor networks comprising small wireless sensor devices facilitate the collection of environmental information and increase the efficiency of outdoor practices, including agriculture. However, the sensor-device installation density of a network is limited because conventional sensor devices must be removed after use. In this study, a sustainable dense sensing system that combines simplified degradable sensor devices, wireless power supply, and thermal-camera image-based information recognition is proposed. The proposed wireless-power-driven sensor device comprises a biodegradable nanopaper substrate, natural wax, and an eco-friendly tin conductive line. The sensor device emits a thermal signal based on the soil moisture content. The thermal camera simultaneously acquires the soil moisture-content data and sensor-device location. The majority of the sensor-device components are biodegradable, and the residual components have a minimal adverse impact on the environment. Additionally, the fertilizer component in the substrate promotes plant growth. The proposed sensing concept introduces a novel direction for realizing hyperdense sensor networks and contributes to the development of social systems that combine sustainability with meticulous environmental management.Kasuga T., Mizui A., Koga H., et al. Wirelessly Powered Sensing Fertilizer for Precision and Sustainable Agriculture. Advanced Sustainable Systems , (2023); https://doi.org/10.1002/adsu.202300314

Frequency-tunable and absorption/transmission-switchable microwave absorber based on a chitin-nanofiber-derived elastic carbon aerogel

The increasing use of microwaves in wireless communications has caused severe electromagnetic pollution. As the frequency range for wireless communication is expanding, it is highly desirable to develop a microwave absorber that can smartly and reversibly tune its absorption and transmission properties on demand to transmit required frequencies and absorb unwanted frequencies. Herein, an absorption-frequency-tunable and absorption/transmission-switchable microwave absorber is developed based on the controlled compression of a chitin-derived elastic carbon aerogel. The maximum absorption frequency is tuned from 10.4 to 11.0, 11.5, and 12.1 GHz by varying the compression strain from 0 to 20, 40, and 60%, respectively, while the maximum absorption intensity is maintained at approximately −40 dB. This frequency-tunable absorption is achieved by reducing the thickness of the carbon aerogel while retaining its moderate dielectric loss tangent. Further compression from 60 to 80% switches the carbon aerogel from being a microwave absorber to transmitter while causing impedance mismatch and changing its dielectric loss tangent from moderate to low levels. The frequency tunability and microwave absorption/transmission switching capability are reversible and repeatable for at least 60,000 cycles of compression and recovery. This study provides insights into the smart and reversible control of microwave absorbing properties and paves the way for multifunctional and robust absorbers.Li X., Zhu L., Kasuga T., et al. Frequency-tunable and absorption/transmission-switchable microwave absorber based on a chitin-nanofiber-derived elastic carbon aerogel. Chemical Engineering Journal 469, 144010 (2023); https://doi.org/10.1016/j.cej.2023.144010

Uniformly connected conductive networks on cellulose nanofiber paper for transparent paper electronics

We demonstrate the fabrication of highly transparent conductive networks on a cellulose nanofiber paper, called cellulose nanopaper. Uniform coating of the conductive nanomaterials, such as silver nanowires (AgNWs) and carbon nanotubes, is achieved by simple filtration of their aqueous dispersions through the cellulose nanopaper, which acts as both filter and transparent flexible substrate. The as-prepared AgNW networks on the nanopaper offer sheet resistance of 12Xsq.Ω1 with optical transparency of 88%, which is up to 75 times lower than the sheet resistance on a polyethylene terephthalate film prepared by conventional coating processes. These results indicate that the 'filtration coating' provides uniformly connected conductive networks because of drainage in the perpendicular direction through paper-specific nanopores, whereas conventional coating processes inevitably cause self-aggregation and uneven distribution of the conductive nanomaterials because of the hard-to-control drying process, as indicated by the well-known coffee-ring effect. Furthermore, the conductive networks are embedded in the surface layer of the nanopaper, showing strong adhesion to the nanopaper substrate and providing foldability with negligible changes in electrical conductivity. This filtration process is thus expected to offer an effective coating approach for various conductive materials, and the resulting transparent conductive nanopaper is a promising material for future paper electronics.Koga, H., Nogi, M., Komoda, N. et al. Uniformly connected conductive networks on cellulose nanofiber paper for transparent paper electronics. NPG Asia Mater 6, e93 (2014). https://doi.org/10.1038/am.2014.9

Nanocellulose Paper Semiconductor with a 3D Network Structure and Its Nano-Micro-Macro Trans-Scale Design

Semiconducting nanomaterials with 3D network structures exhibit various fascinating properties such as electrical conduction, high permeability, and large surface areas, which are beneficial for adsorption, separation, and sensing applications. However, research on these materials is substantially restricted by the limited trans-scalability of their structural design and tunability of electrical conductivity. To overcome this challenge, a pyrolyzed cellulose nanofiber paper (CNP) semiconductor with a 3D network structure is proposed. Its nano-micro-macro trans-scale structural design is achieved by a combination of iodine-mediated morphology-retaining pyrolysis with spatially controlled drying of a cellulose nanofiber dispersion and paper-crafting techniques, such as microembossing, origami, and kirigami. The electrical conduction of this semiconductor is widely and systematically tuned, via the temperature-controlled progressive pyrolysis of CNP, from insulating (1012 ω cm) to quasimetallic (10-2 ω cm), which considerably exceeds that attained in other previously reported nanomaterials with 3D networks. The pyrolyzed CNP semiconductor provides not only the tailorable functionality for applications ranging from water-vapor-selective sensors to enzymatic biofuel cell electrodes but also the designability of macroscopic device configurations for stretchable and wearable applications. This study provides a pathway to realize structurally and functionally designable semiconducting nanomaterials and all-nanocellulose semiconducting technology for diverse electronics.Koga H., Nagashima K., Suematsu K., et al. Nanocellulose Paper Semiconductor with a 3D Network Structure and Its Nano-Micro-Macro Trans-Scale Design. ACS Nano, 16(6), 8630-8640, 2022. https://doi.org/10.1021/acsnano.1c10728

Cellulose nanofiber paper as an ultra flexible nonvolatile memory

On the development of flexible electronics, a highly flexible nonvolatile memory, which is an important circuit component for the portability, is necessary. However, the flexibility of existing nonvolatile memory has been limited, e.g. the smallest radius into which can be bent has been millimeters range, due to the difficulty in maintaining memory properties while bending. Here we propose the ultra flexible resistive nonvolatile memory using Ag-decorated cellulose nanofiber paper (CNP). The Ag-decorated CNP devices showed the stable nonvolatile memory effects with 6 orders of ON/OFF resistance ratio and the small standard deviation of switching voltage distribution. The memory performance of CNP devices can be maintained without any degradation when being bent down to the radius of 350 μm, which is the smallest value compared to those of existing any flexible nonvolatile memories. Thus the present device using abundant and mechanically flexible CNP offers a highly flexible nonvolatile memory for portable flexible electronics.Nagashima, K., Koga, H., Celano, U. et al. Cellulose Nanofiber Paper as an Ultra Flexible Nonvolatile Memory. Sci Rep 4, 5532 (2014). https://doi.org/10.1038/srep05532

Optically transparent nanofiber sheets by deposition of transparent materials: A concept for a roll-to-roll processing

Deposition of transparent materials on cellulose nanofiber sheets enhanced the transparency of nanofiber sheets. The coated nanofiber sheets exhibited high transparency regardless of the wide distribution of refractive indexes of the coated resins, and the loss of transparency compared with the theoretical values was less than 2.5%. The low coefficient of thermal expansion of the nanofiber sheets (8.5 ppm/K) was maintained after the coating. The continuous coating of functional transparent materials on the nanofiber sheets is a promising approach toward accomplishing a simple roll-to-roll manufacturing process