Viscoelastic behavior in rheological characterization of a coal-based colloidal composite binder

The rheological properties of a coal-based colloidal composite binder (3Co-binder) with emphasis on viscoelastic behavior were investigated. Dynamic oscillatory rheometry integrated with the time-temperature superposition (TTS) principle was employed to analyze the evolution of viscoelastic moduli (storage modulus and loss modulus) under varying temperatures, frequencies, and time, revealing the mechanistic link between microscopic network structures and macroscopic rheological responses. The 3Co-binder exhibits a wide linear viscoelastic region (up to 14.7% shear strain amplitude), indicating superior resistance to shear-induced structural damage. The viscoelastic moduli decrease significantly with rising temperature, accompanied by irreversible thermal hysteresis, necessitating the avoidance of thermal cycling applications. Frequency sweep tests demonstrate that high-viscosity binders exhibit enhanced resistance to shear-induced structural damage under high-frequency shear (80-100 rad s^-1). The generalized Maxwell model (four-order) successfully fitted the frequency-dependent viscoelastic response, uncovering characteristics of multiple relaxation time. The approximate value between the structural activation energy and viscous flow activation energy of the binder endows it with both exceptional shear-thinning properties and self-healing functionalities. As the apparent viscosity of the binder increases from 2411 to 8041 mPa s, the structural relaxation activation energy increases from 51.05 to 62.66 kJ/mol. Cryogenic scanning electron microscopy analysis further confirmed that high-viscosity binders form a dense three-dimensional network structure, enhancing mechanical strength at the expense of dispersibility.