Rheo-impedance analysis enables simultaneous monitoring of viscoelastic and electrochemical evolution during drying. Mechanical and electrochemical percolation transitions occur at distinct residual solvent contents. Drying temperature governs the competition between network rigidification and conductive pathway disruption. The method provides process-relevant insight into transport-limited behavior in colloidal systems. Pigment-based inks are widely used for their superior durability, color quality, and reliability for inkjet printing. However, pigment particles tend to aggregate during drying, often causing nozzle clogging and film inhomogeneity. To address this issue, we applied rheo-impedance analysis—a dynamic and non-destructive technique capable of simultaneously measuring viscoelastic and electrochemical responses during solvent evaporation—to investigate the structural and electrochemical evolution of pigment-based inks under different drying temperatures. Using a commercial black pigment ink, we measured the time-dependent changes in the storage modulus (G’), impedance magnitude (|Z|), and electrical resistance (R, determined by an equivalent-circuit analysis) at controlled temperatures between 40°C and 60°C. The drying process proceeded through three distinct stages—constant-rate, falling-rate, and terminal—separated by transition points at approximately 60% and 28% evaporation residues. Mechanical percolation occurred at an evaporation residue of ∼60% (solid fraction ≈ 40%) regardless of temperature, whereas electrochemical percolation emerged earlier at higher temperatures due to fragmentation of the continuous water pathways. These findings demonstrate that mechanical and electrochemical percolation evolve on different spatial and temporal scales during drying, and that rheo-impedance analysis provides a quantitative means of visualizing this dual-percolation behavior. The insights obtained here offer a powerful framework for understanding and controlling drying-induced structural evolution in functional inks, with broader implications for colloidal drying, interfacial transport, and thin-film formation.
Yamagata et al. (Wed,) studied this question.