Glass has well-suited low thermal expansion for use in electronic devices, but it is fragile, and the search for a stronger, more flexible optically clear medium has gone on for many years. Plastics have been widely studied; however, most of them have large coefficients of thermal expansion (CTE, approx. 50 ppm K À1 ), and foldable plastics in particular exhibit extremely large CTEs, in excess of 200 ppm K À1. Further, the functional materials deposited on plastic substrates are prone to be damaged by the temperatures involved in the assembly and mounting processes due to the mismatch between CTEs from different materials. This article reports on what might be best described as optically transparent paper. It is a foldable nanofiber material with low thermal expansion (CTE <8.5 ppm K À1 ) prepared using 15 nm cellulose nanofibers with the same chemical constituents as conventional paper and a production process also similar to that of conventional paper. The only difference is in the fiber width and the size of the interstitial cavities (Fig. 1). The foldable, low-CTE, and optically transparent nanofiber paper is the perfect candidate for substrates for continuous roll-to-roll processing in the future production of electronic devices, such as flexible displays, solar cells, e-papers, and a myriad of new flexible circuit technologies, and could replace the costly conventional batch processes based on glass substrates currently used. [1][2][3][4][5] We project that it will also replace conventional paper as an advanced information medium, which can still be produced using traditional paper-making equipment that is used in production today.Cellulose nanofibers are the main component of plant and wood pulp fibers. These tiny elements with diameters of 15-20 nm are composed of bundles of cellulose microfibrils smaller than 4 nm in width, which, in turn, are composed of long cellulose molecules laterally stabilized by hydrogen bonds forming highly crystalline domains. As such, cellulose nanofibers have a CTE of 0.1 ppm K À1 , [6] which is as low as that of quartz glass, and an estimated strength of 2-3 GPa, [7] rendering it five times stronger than mild steel. The nanofibers also exhibit good heat-transfer properties comparable to glass.[8] Another significant property of the nanofibers is that light scattering can be suppressed. [9,10] If the cellulose nanofibers are densely packed, and the interstices between the fibers are small enough to avoid light scattering, the cellulosic material becomes transparent while maintaining the high performance of the material described before.To obtain the nanofibers from plants and wood fibers, it is necessary to disassemble the fibers' original structure. The cell walls of the fibers are composed of several thin layers, in which the cellulose nanofibers are oriented in various directions and embedded in matrix substances. In order to extract uniform nanofibers from this complex structure, wood flour was used as a starting material. The wood flour was ground in a water-swollen cond...

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The elastic modulus of single microfibrils from tunicate (Halocynthia papillosa) cellulose was measured by atomic force microscopy (AFM). Microfibrils with cross-sectional dimensions 8 × 20 nm and several micrometers in length were obtained by oxidation of cellulose with 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) as a catalyst and subsequent mechanical disintegration in water and by sulfuric acid hydrolysis. The nanocellulosic materials were deposited on a specially designed silicon wafer with grooves 227 nm in width, and a three-point bending test was applied to determine the elastic modulus using an AFM cantilever. The elastic moduli of single microfibrils prepared by TEMPO-oxidation and acid hydrolysis were 145.2 ± 31.3 and 150.7 ± 28.8 GPa, respectively. The result showed that the experimentally determined modulus of the highly crystalline tunicate microfibrils was in agreement with the elastic modulus of native cellulose crystals.

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