Abstract
Cellulose nanofibers (CNFs) are promising for various applications such as substrates of flexible devices and reinforcement materials. Most of these applications require control of the drying process of the aqueous CNF dispersions. However, the existing reports examine the surface of dried materials because scanning electron microscopy (SEM) and atomic force microscopy (AFM) are not compatible with either the wet conditions or structure inside the materials. We report the characterization of these aqueous dispersions by the use of optical microscopy although it cannot be used directly to observe CNFs. We add a small portion of colloidal particles into the samples and obtain their trajectory data. The trajectories of Brownian motion include information on the surrounding environments. We analyze the microscopy movie data from the viewpoint of statistical mechanics, and reveal the mesoscale characteristics beyond viscosity. In particular, the possible non-uniformity of the dispersion is quantitatively examined through the framework of the generalized diffusion.
Highlights
Today, cellulose nano bers (CNFs)[1] are well known as environmentally friendly materials, promising for various applications ranging from nanopapers to reinforcements.[2]
While optical coherence tomography (OCT) is mainly used for the ow of the sample and X-rays are used for the static structural properties such as anisotropy, we focus on the characteristics especially when the Cellulose nanofibers (CNFs) are combined with colloidal particles
In order to discuss the time evolution of mean squared displacements (MSDs), we evaluated the MSDs with different time spans Dt
Summary
Cellulose nano bers (CNFs)[1] are well known as environmentally friendly materials, promising for various applications ranging from nanopapers to reinforcements.[2]. Even if the drying is not performed in the state of droplets, the drying temperature and difference of composition can affect the nal dried-up state[36,37] and generally affects the morphology.[33,38,39] Even the initial concentration of CNFs can affect the transparency of the nanopaper.[12] Many hydrogen bonds between the laments of CNFs are formed during the drying of the aqueous dispersion This stage determines the nal structure of CNF-based materials such as nanopapers. The characterization of an aqueous CNF dispersion at the mesoscale between the single lament level and the overall continuum level is desired This is partly realized by optical coherence tomography (OCT)[42] and further by X-ray scattering,[43,44] but other visualization techniques of wet states are based on the macroscopic rheology.[45,46]. The particle dynamics itself is directly important in the development of nanocomposites made from mixtures of CNFs and colloidal particles
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