Graphical Abstract

Single particle/molecule tracking is widely used for the evaluation of diffusion coefficients using diverse tracking algorithms. Many of them require the subtle decision of displacement threshold parameter to enable the appropriate tracking, though it depends on both of the diffusion coefficient itself and the measurement system. A simple and highly transferable technique is proposed to overcome this difficulty based on the evaluation of diffusion coefficient from the peak position of the distribution of squared displacements in the logarithmic scale. In combination with its linear dependence on time, this protocol is remarkably robust against the too large value of the displacement threshold including that covers the whole image. Furthermore, the proposed technique is compatible with many of the existing algorithms by construction.

Industrial applications of cellulose nanofibres (CNFs) include the additive to a wide range of materials from display and cosmetic to pigment inks. Many of these expected applications are based on the mixture of colloidal particles and CNFs in aqueous dispersion. In particular, the mixed dispersion is typically processed in such a way that the droplet or shallow wide volume of dispersion is dried on the substrate or container. In this work, the basic physical properties that these diverse kinds of potential applications share in common are focused on. The colloidal films were fabricated consisting of polystyrene particles and CNFs under the condition of various concentration combinations through the drying of aqueous dispersion in polystyrene well plates. It has been found that the films fabricated from higher concentrations of CNF tend to peel-off spontaneously in the drying process. The basic mechanism of phenomenon is attributed to the contraction of CNFs during the drying by hydrogen bonding between the filaments.

Promising versatile applications of cellulose nanofibres (CNFs) include film structures for device substrates and surface coatings. Although there are various factors that affect the textures of such 'nanopapers', the drying from aqueous dispersion of CNF is the typical process to fabricate them. The basic property on this drying process is focused on, paying attention to the influence of temperature on the macroscopic uniformity. On the one hand, higher drying temperature is advantageous for the fast fabrication. On the other hand, too high temperature leads to significant nonuniformity, are focused on of the film. They propose that this drawback is suppressed by the multi-step coating process. The multi-step coating technique is simple without extra introduction of apparatus or chemical species. Therefore, it is a good option, e.g. when trying to fabricate relatively thin film structures where coffee-ring-like phenomena tend to take place.

We propose a technique to evaluate the field of diffusion coefficient for particle dispersion where the Brownian motion is heterogeneous in space and single particle tracking (SPT) analysis is hindered by high concentration of the particles and/or their small size. We realize this “particle image diffusometry” by the principle of the differential dynamic microscopy (DDM). We extend the DDM by introducing the automated objective decision of the scaling regime itself. Label-free evaluation of spatially non-uniform diffusion coefficients without SPT is useful in the diverse applications including crystal nucleation and glass transition where non-invasive observation is desired.