Emergent rheological nonuniformity of hydrogel from drying fiber suspension

In contrast to the densely packed solid structures of crystals or glasses, gels can take a wide range of concentrations for the suspended medium. The consequent structures are random networks that support the fluid. Therefore, structural characteristics are fundamentally diverse. Drying of a colloidal suspension in liquid can cause gelation by an increase in concentration. The nonequilibrium process of drying can be affected by the initial condition. In this article, we report the structural variation of the hydrogel triggered by the difference in initial concentration. We employ cellulose nanofibers to form hydrogels in the drying process of aqueous dispersion. The structural characteristics of hydrogel are rheologically evaluated by the dynamics of dispersed probe particles through optical microscopy movie data analysis based on the single particle tracking. In particular, we focus on the nonuniformity in the structure through multimodality of probe diffusion. The nonuniformity of the hydrogel structure emerges in the specific combination range of initial and transient concentrations, characteristic to the nonequilibrium nature in terms of path dependence of the process.