Self-Alignment Sequence of Colloidal Cellulose Nanofibers Induced by Evaporation from Aqueous Suspensions

Abstract

Cellulose nanopapers fabricated by drying aqueous colloidal suspensions of cellulose nanofibers (CNFs) have characteristic hierarchic structures, which cause the problem that their optical properties, including their transparency or haze, vary due to the drying processes affecting CNF alignment. It is unclear when and how the colloidal CNFs align in the evaporation–condensation process from the randomly dispersed suspension to form the nanopaper. In this study, we found that the CNFs undergo a self-alignment sequence during the evaporation–condensation process to form chiral nematic nanopaper by observing the birefringence of the drying suspensions from both the top and side for two suspensions with different initial CNF concentrations. The layer structures of the CNFs first form on the surface by condensation of the suspension, owing to water evaporation from the surface. The thickness of the layered structure then increases and the CNFs begin to align within each layer plane, finally forming chiral nematic structures. A birefringence difference also occurs for dried nanopapers with similar transparency or haze because of the initial CNF concentration.

Alignment of Cellulose Nanofibers: Harnessing Nanoscale Properties to Macroscale Benefits

“…As mentioned earlier, this may be attributable to the longer diffusion times of long CNF particles. Other studies have shown that evaporation/condensation of CNFs can exhibit self-organizing behavior. , Uetani et al observed self-organization of a chiral nematic phase during evaporation and identified the concentration at which the onset of self-organization began at the surface where evaporation was occurring …”

“…91,92 Uetani et al observed selforganization of a chiral nematic phase during evaporation and identified the concentration at which the onset of selforganization began at the surface where evaporation was occurring. 91 Spinning-Induced Alignment. Fiber spinning comprises an array of fiber formation processes that produce continuous filaments.…”

Estimation of the Intrinsic Birefringence of Cellulose Using Bacterial Cellulose Nanofiber Films

“…Densely packed films made of cellulose nanofibers (CNFs) are promising materials for optoelectronics, such as flexible displays and electronic paper, owing to their flexibility and high dimensional stability against the temperature change of each single CNF. , For these optoelectronics, light compensation films, such as polarizers, phase difference films, and backlight films, with large optical anisotropy are essential to control the retardation (i.e., birefringence) owing to polymer chain alignment, , and they are also indispensable to improve the contrast or reduce the rainbow unevenness and light leakage . CNF films are known to show some birefringence when the constitutive CNFs anisotropically align, and CNFs consisting of an extended chain crystal of cellulose molecules are also considered to have large birefringence. , However, the intrinsic birefringence of cellulose, which is the origin to the birefringence of CNF films, greatly varies between cellulose samples, and its estimation represents a bottleneck for producing light compensation films with CNFs to develop high-performance next-generation optoelectronics.…”

Inherently Distinctive Potentialities and Uses of Nanocellulose Based on its Nanoarchitecture

“…However, cast-drying requires a very long drying time, and the casting method results in drying-induced local condensation. Therefore, the evaporation process affects the self-assembly modes of nanocellulose and determines the final film structure (Uetani et al 2018). To avoid lengthy drying and uncontrolled selfassembly, a new high-speed drying technique has recently been developed.…”