Study on the Rheological Properties of MC-Based Thermosensitive Gel Foam for Coal Spontaneous Combustion Prevention

Abstract

To improve thermoresponsive gel foams for coal spontaneous combustion prevention, the effects of temperature, expansion ratio, and inorganic salts on their rheology, water retention, and film-forming properties were systematically investigated. The results demonstrated that the gel foam exhibited typical yield–pseudoplastic behavior governed by temperature-induced network formation and shear-induced structural disruption. At 60 °C, hydrophobic association promoted a three-dimensional gel network, significantly enhancing apparent viscosity and viscoelasticity and extending the linear viscoelastic region by approximately 11 percentage points compared with 40–55 °C. Under high shear, disruption of the gel network and bubble structure induced pronounced shear thinning, which was well described by the Herschel–Bulkley model. The expansion ratio exhibited a threshold effect: above 4, further increases in viscosity and flow resistance gradually approached saturation owing to the dynamic balance between bubble densification and liquid-film thinning. Inorganic salts regulated foam properties by modifying the gel network and water distribution. Ca2+ enhanced network compactness and water retention through a bridging-enhancement/shielding-disruption mechanism coupled with strong hydration, whereas Na+ acted mainly through electrostatic shielding. Salt-containing foams exhibited improved water retention but reduced film-forming ability, indicating that foam stability is jointly controlled by interfacial viscoelasticity, network cross-linking, water-state distribution, and gas diffusion. These findings elucidate the rheological regulation of thermoresponsive gel foams under coupled thermal–saline conditions and provide a theoretical basis for designing high-performance materials for coal-fire prevention.