Propriedades reológicas de nanofluidos com base newtoniana e não newtoniana

Abstract

This work presents a comparative investigation of the rheological properties of nanofluids formulated with silica (SiO₂) and graphene graphene nanoplatelets dispersed in Newtonian (mineral oil) and non-Newtonian (0.15% Carbopol®) bases, with the aim of elucidating how surface chemistry, particle morphology, and the physicochemical characteristics of the liquid matrix modulate microstructure and mechanical response under different shear regimes. The motivation stems from the growing relevance of nanofluids in industrial and energy applications, in which colloidal stability, viscosity, elasticity, and transient behavior are critical to performance. Four nanofluid systems were prepared: mineral oil + silica, mineral oil + graphene nanoplatelets (with and without carnauba wax), Carbopol® + silica, and Carbopol® graphene nanoplatelets, and characterized through steady and transient rheometry, oscillatory testing, FTIR spectroscopy, and zeta potential measurements. The results reveal markedly distinct microstructural behaviors across matrices: in mineral oil, silica promotes the gradual formation of interconnected structures capable of sustaining elasticity, accompanied by increases in viscosity, emergence of yield behavior, and shear-thickening at high shear rates; conversely, graphene nanoplatelets acts as a structural weakening agent within the semicrystalline carnauba-wax network, reducing rigidity and structural cohesion. In Carbopol® systems, both nanomaterials substantially affect the internal organization of the polymeric network: silica modifies connectivity among microgel domains in a concentration-dependent manner, whereas graphene nanoplatelets disrupts structural cohesion, leading to reductions in elasticity, viscosity, and yield stress. Transient tests reveal thixotropic or antithixotropic regimes depending on particle type and matrix, indicating structural rearrangements strongly dependent on deformation and time history. FTIR analyses corroborate the molecular mechanisms underlying particle–matrix and particle–particle interactions, providing insight into the observed rheological transitions. Overall, the findings show that the rheological response of nanofluids is governed by the interplay between medium polarity, nanoparticle morphology, and the intensity of interfacial interactions, offering a framework for the rational design of advanced systems for fluid engineering, energy applications, and multiphase processing.