Pournorouz Zahra, Mostafavi Amirhossein, Pinto Aditya, Bokka Apparao, Jeon Junha, Shin Donghyun
Mechanical and Aerospace Engineering, The University of Texas at Arlington, Arlington, TX, 76019-0023, USA.
Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, TX, 76019-0065, USA.
Nanoscale Res Lett. 2017 Dec;12(1):29. doi: 10.1186/s11671-016-1802-1. Epub 2017 Jan 11.
For the last few years, molten salt nanomaterials have attracted many scientists for their enhanced specific heat by doping a minute concentration of nanoparticles (up to 1% by weight). Likewise, enhancing the specific heat of liquid media is important in many aspects of engineering such as engine oil, coolant, and lubricant. However, such enhancement in specific heat was only observed for molten salts, yet other engineering fluids such as water, ethylene glycol, and oil have shown a decrease of specific heat with doped nanoparticles. Recent studies have shown that the observed specific heat enhancement resulted from unique nanostructures that were formed by molten salt molecules when interacting with nanoparticles. Thus, such enhancement in specific heat is only possible for molten salts because other fluids may not naturally form such nanostructures. In this study, we hypothesized such nanostructures can be mimicked through in situ formation of fabricated nano-additives, which are putative nanoparticles coated with useful organic materials (e.g., polar-group-ended organic molecules) leading to superstructures, and thus can be directly used for other engineering fluids. We first applied this approach to polyalphaolefin (PAO). A differential scanning calorimeter (DSC), a rheometer, and a customized setup were employed to characterize the heat capacity, viscosity, and thermal conductivity of PAO and PAO with fabricated nano-additives. Results showed 44.5% enhanced heat capacity and 19.8 and 22.98% enhancement for thermal conductivity and viscosity, respectively, by an addition of only 2% of fabricated nanostructures in comparison with pure PAO. Moreover, a partial melting of the polar-group-ended organic molecules was observed in the first thermal cycle and the peak disappeared in the following cycles. This indicates that the in situ formation of fabricated nano-additives spontaneously occurs in the thermal cycle to form nanostructures. Figure of merit analyses have been performed for the PAO superstructure to evaluate its performance for heat storage and transfer media.
在过去几年中，熔盐纳米材料因其通过掺杂微量纳米颗粒（重量百分比高达1%）而提高的比热吸引了众多科学家。同样，提高液体介质的比热在工程的许多方面都很重要，如发动机油、冷却液和润滑剂。然而，这种比热的提高仅在熔盐中观察到，而其他工程流体如水、乙二醇和油在掺杂纳米颗粒后比热却有所下降。最近的研究表明，观察到的比热提高是由于熔盐分子与纳米颗粒相互作用时形成的独特纳米结构所致。因此，这种比热的提高仅对熔盐是可能的，因为其他流体可能不会自然形成这种纳米结构。在本研究中，我们假设可以通过原位形成人造纳米添加剂来模拟这种纳米结构，这些人造纳米添加剂是涂覆有用有机材料（如极性基团末端有机分子）的假定纳米颗粒，从而形成超结构，因此可直接用于其他工程流体。我们首先将这种方法应用于聚α烯烃（PAO）。使用差示扫描量热仪（DSC）、流变仪和定制装置来表征PAO以及添加人造纳米添加剂的PAO的热容量、粘度和热导率。结果表明，与纯PAO相比，仅添加2%的人造纳米结构，热容量提高了44.5%，热导率提高了19.8%，粘度提高了22.98%。此外，在第一个热循环中观察到极性基团末端有机分子的部分熔化，且该峰在随后的循环中消失。这表明人造纳米添加剂的原位形成在热循环中自发发生以形成纳米结构。已对PAO超结构进行了品质因数分析，以评估其作为储热和传热介质的性能。
