RHEOLOGICAL BEHAVIOR OF A SILVER AQUEOUS NANOFLUID STABILIZED WITH AMINOSILANE-BASED SURFACTANT UNDER CONFINED FLOW

ABSTRACT The rheological behavior of an aqueous suspension of silver nanoparticles stabilized with aminosilane-based surfactant flowing under confinement was investigated. Three stability levels were defined based on the zeta potential: high (41.73 mV, pH 4.3), medium (10.44 mV, pH 7.4), and low (0.74 mV, pH 8.6). Furthermore, the preliminary investigation showed that the surface charge remained positive, and the formation of agglomerates was not observed. Due to the particle coating and the ionization of the amino groups of the surfactant an electrosteric stabilization was evidenced. Shear rates ranging from 50 to 1000 s-1 and shear stresses between 0.02 and 0.2 Pa, at the temperatures of 15, 25 and 35 ºC, were evaluated with the nanofluid flowing in microchannels with a gap of 100, 300 and 500 µm. A trend to dilatant behavior was observed at high shear rate and a slit size of 500 µm, while Newtonian behavior was predominant at lower slit sizes. A reduction of 47.3% was noticed at 25 ºC with the variation in the slit size from 500 to 300 µm. Furthermore, the viscosity of the nanofluid decreased as much as 60% when the slit size was reduced from 500 to 100 µm.