Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune 411008, India; Academy of Scientific and Innovative Research (AcSIR), CSIR-National Chemical Laboratory, Pune 411008, India.
Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory, Pune 411008, India; Academy of Scientific and Innovative Research (AcSIR), CSIR-National Chemical Laboratory, Pune 411008, India.
J Colloid Interface Sci. 2017 Nov 15;506:162-168. doi: 10.1016/j.jcis.2017.07.038. Epub 2017 Jul 14.
To study the role of unsaturation in the surfactant molecule on the thermal conductivity of magnetite nanofluids, four different fatty acid (stearic, oleic, linoleic, and linolenic acids with different degree of unsaturation) coated magnetite nanoparticles of comparable size are prepared and dispersed in toluene. It is found that the nanofluid with the saturated fatty acid coated nanoparticles show larger viscosity than the fluid with the unsaturated fatty acid coated particles at all concentrations. Thermal conductivity studies show enhancement only above a critical concentration for all fluids. The critical concentration for thermal conductivity enhancement varies with the surfactant, possibly due to the difference in the degree of aggregation of the nanoparticles in the fluid, because of the difference in the conformation of the surfactant molecules on the nanoparticle's surface. The experimental thermal conductivity follows the Maxwell model at higher concentrations. From the overall studies, it is observed that the thermal conductivity of the fluids with aggregated or assembled nanoparticles shows slightly larger enhancement than that of the fluids with isolated particles. However, in the presence of a magnetic field, the fluids with isolated nanoparticles showed relatively larger enhancement, possibly due to the easy response of the isolated magnetite nanoparticles to the applied field.
为了研究表面活性剂分子中的不饱和度对磁铁矿纳米流体导热系数的影响，我们制备了四种不同不饱和度的脂肪酸（硬脂酸、油酸、亚油酸和亚麻酸）包覆的磁铁矿纳米粒子，并将它们分散在甲苯中。研究发现，在所有浓度下，饱和脂肪酸包覆的纳米粒子形成的纳米流体的粘度都比不饱和脂肪酸包覆的粒子形成的纳米流体大。导热系数研究表明，所有流体在超过临界浓度时才会增强。临界浓度的增强因表面活性剂的不同而不同，这可能是由于纳米粒子在流体中的聚集程度不同，因为表面活性剂分子在纳米粒子表面的构象不同。在较高浓度下，实验得到的导热系数符合 Maxwell 模型。从整体研究来看，与具有孤立粒子的流体相比，具有聚集或组装粒子的流体的导热系数增强略大。然而，在存在磁场的情况下，具有孤立纳米粒子的流体显示出相对较大的增强，这可能是由于孤立的磁铁矿纳米粒子对施加的磁场的响应较为容易。
