Dual rheological responses in Ag pastes

Highly concentrated suspensions have complex structures that complicate their characterization and study. Highly concentrated suspensions of Ag particles in ethyl cellulose solutions (Ag pastes) were thus studied and dual rheological responses were observed. Under rotational shear, the unpredicted enhancement of shear moduli occurred in the low frequency regime, showing that rheological responses of Ag pastes were strongly influenced by fillers. Under large-amplitude oscillation, the hydrodynamic-induced enhancement effect was observed over the whole frequency range, showing that rheological responses of Ag pastes were dominated by the binder solutions. Further studies showed that this dual behavior arose from the dual nature of structures in Ag pastes. The different shear types promoted the development of different structures in rheological experiments. Rotational shear promoted cluster formation, resulting in the unpredicted enhancement; while large-amplitude oscillation broke the clustering, leading to the hydrodynamic enhancement.