Colloidal Stability and Transport Property Evolution in Functionalized Carbon Nanomaterial Suspensions at Ultra-Low Loadings

Carbon-based nanomaterial suspensions exhibit complex stability–property relationships that strongly influence their transport behavior. In this study, the colloidal stability and transport property evolution of multi-walled carbon nanotube (MWCNT) and Graphene Nanoplatelets (GNP) suspensions dispersed in a water/ethylene glycol (50:50 wt.%) mixture were systematically investigated at ultra-low loadings (0.005–0.05 wt.%). Surface functionalization using oleic acid was employed to assess its influence on dispersion quality and interfacial interactions. Stability was evaluated through UV–Vis spectrophotometry over time, revealing concentration-dependent sedimentation behavior and improved dispersion persistence in functionalized systems. Thermal conductivity, dynamic viscosity, density, and specific heat capacity were analyzed within the temperature range of 20–70 °C to examine the coupling between colloidal structure and transport properties. Results indicate that enhanced dispersion stability promotes measurable thermal conductivity gains while moderating viscosity penalties at ultra-dilute regimes. Functionalized MWCNT suspensions exhibited improved stability and more favorable thermophysical balance compared to non-functionalized counterparts. To generalize concentration-dependent trends, supervised regression techniques were employed to establish transferable predictive relationships between stability metrics and transport properties. The developed models demonstrated high predictive reliability (R 2 up to 0.999), enabling cross-concentration estimation and inverse identification of property evolution. Overall, this work advances the understanding of dilute nanofluids by linking stability evolution to transport behavior, providing a predictive framework for designing stable and functionally optimized colloidal systems.