Abstract
It is essential to build multiaxis oriented nanocellulose films in the plane for developing thermal or optical management films. However, using conventional orientation techniques, it is difficult to align nanocelluloses in multiple directions within the plane of single films rather than in the thickness direction like the chiral nematic structure. In this study, we developed the liquid-phase three-dimensional (3D) patterning technique by combining wet spinning and 3D printing. Using this technique, we produced a checkered film with multiaxis oriented nanocelluloses. This film showed similar retardation levels, but with orthogonal molecular axis orientations in each checkered domain as programmed. The thermal transport was enhanced in the domain with the oriented pattern parallel to the heat flow. This liquid-phase 3D patterning technique could pave the way for bottom-up design of differently aligned nanocellulose films to develop sophisticated optical and thermal materials.
Highlights
Nanocelluloses extracted from natural resources have large dimensional and functional anisotropy derived from their intrinsic extended chain crystal of cellulose I, so the various oriented structures of nanocelluloses have stunning properties in various materials including actuating plant cell walls [1], photonic structures with the chiral nematic phase [2,3], and fibers [4,5,6,7] or films [8,9] with high mechanical strength
Recent studies have revealed that unidirectionally oriented nanocellulose films anisotropically conduct heat [10] or control optical retardation [11]
To evaluate the orientational effect of liquid-phase 3D patterning, we programmed a unidirectional pattern with a programmed area of 18 mm × 50 mm for tunicate cellulose nanowhiskers (TNWs) and tunicate cellulose nanofibers (TNFs) suspensions with different concentrations, and produced films with various patterning conditions including the needle diameter and discharging and patterning speeds, as summarized in Table 1 and Figure S1
Summary
Nanocelluloses extracted from natural resources have large dimensional and functional anisotropy derived from their intrinsic extended chain crystal of cellulose I, so the various oriented structures of nanocelluloses have stunning properties in various materials including actuating plant cell walls [1], photonic structures with the chiral nematic phase [2,3], and fibers [4,5,6,7] or films [8,9] with high mechanical strength. With regard to the thermal conductivity and optical controllability of nanocelluloses, for future paper electronics, the development of sophisticated materials such as phonon management film elements or polarizing arrays is expected by constructing fine multidirectional alignment structures within the film planes, rather than in the thickness direction like the self-assembling chiral nematic structure. For these purposes, it remains a great challenge to develop a practical orientation technique to multiaxis arrange the various nanocellulose alignments within the single film plane. We need to combine the unidirectionally aligned nanocellulose parts to build multiaxis oriented nanocellulose films, but this is unrealistic because once dried, cellulose papers do not adhere to each other
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