CNR-IENI, Corso Stati Uniti 4, I-35127 Padova, Italy.
Nanotechnology. 2013 Sep 13;24(36):365601. doi: 10.1088/0957-4484/24/36/365601. Epub 2013 Aug 13.
With the aim of preparing stable nanofluids for heat exchange applications and to study the effect of surfactant on the aggregation of nanoparticles and thermal diffusivity, stable silver colloids were synthesized in water by a green method, reducing AgNO₃ with fructose in the presence of poly-vinylpyrollidone (PVP) of various molecular weights. A silver nanopowder was precipitated from the colloids and re-dispersed at 4 vol% in deionized water. The Ag colloids were characterized by UV-visible spectroscopy, combined dynamic light scattering and ζ-potential measurements, and laser flash thermal diffusivity. The Ag nanopowders were characterized by scanning electron microscopy and thermal gravimetric analysis. It was found that the molecular weight of PVP strongly affects the ζ-potential and the aggregation of nanoparticles, thereby affecting the thermal diffusivity of the obtained colloids. In particular, it was observed that on increasing the molecular weight of PVP the absolute value of the ζ-potential is reduced, leading to increased aggregation of nanoparticles. A clear relation was identified between thermal diffusivity and aggregation, showing higher thermal diffusivity for nanofluids having higher aggregation. A maximum improvement of thermal diffusivity by about 12% was found for nanofluids prepared with PVP having higher molecular weight.
为了制备用于热交换应用的稳定纳米流体并研究表面活性剂对纳米粒子聚集和热扩散率的影响，我们采用绿色方法在水中合成了稳定的银胶体，在聚维酮（PVP）的存在下用果糖还原 AgNO₃，PVP 的分子量不同。从胶体中沉淀出银纳米粉末，并在去离子水中以 4 体积%重新分散。Ag 胶体通过紫外-可见光谱、动态光散射和 ζ-电位测量以及激光闪光热扩散率进行表征。Ag 纳米粉末通过扫描电子显微镜和热重分析进行了表征。研究发现，PVP 的分子量强烈影响 ζ-电位和纳米粒子的聚集，从而影响所得到的胶体的热扩散率。特别是，观察到随着 PVP 分子量的增加，ζ-电位的绝对值降低，导致纳米粒子聚集增加。发现热扩散率与聚集之间存在明显的关系，具有更高聚集度的纳米流体具有更高的热扩散率。对于用具有较高分子量的 PVP 制备的纳米流体，发现热扩散率最大提高了约 12%。
