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.

摘要 本研究针对经氨基硅烷类表面活性剂稳定化的银纳米颗粒水悬浮液在受限流动下的流变行为展开了探究。基于Zeta电位（zeta potential）将悬浮液分为三个稳定等级：高稳定（41.73 mV，pH 4.3）、中稳定（10.44 mV，pH 7.4）与低稳定（0.74 mV，pH 8.6）。此外，初步研究表明体系表面电荷始终为正，且未观察到团聚体生成。由于颗粒包覆作用与表面活性剂氨基的电离作用，体系呈现出电空间位阻稳定效应。本研究在15、25与35 ℃的温度条件下，针对在间隙尺寸为100、300及500 µm的微通道中流动的纳米流体，测试了其50~1000 s⁻¹的剪切速率范围与0.02~0.2 Pa的剪切应力区间。当剪切速率较高且间隙尺寸为500 µm时，体系呈现出胀流行为趋势；而在较小的间隙尺寸下，体系主要表现为牛顿流体特性。在25 ℃条件下，当间隙尺寸从500 µm降至300 µm时，体系黏度降低了47.3%。此外，当间隙尺寸从500 µm降至100 µm时，纳米流体的黏度最高可降低60%。