Yang Ying, Grulke Eric A, Zhang Z George, Wu Gefei
Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506, USA.
J Nanosci Nanotechnol. 2005 Apr;5(4):571-9. doi: 10.1166/jnn.2005.079.
Dispersions containing nanoparticles (nanofluids) are mixtures with unique properties, and their transport properties depend on the three-dimensional network or microstructure of the nanoparticles, which can be affected by various factors including shear stress, particle loading, and temperature. In this research, we studied the rheological behaviors of dispersions containing two different carbon morphologies: multiwalled carbon nanotubes (rodlike nanoparticles with L/D = 30), and graphite particles (disklike nanoparticles with L/D = 0.025). All nanofluids showed shear thinning behavior in steady shear measurements and those containing nanotubes had lower power law indices than graphite dispersions. Shear stress broke down the microstructure network and oriented both rodlike and disklike nanoparticles in the dispersions. The presence of a modest amount of nanotubes in the graphite nanofluid affected the microstructure of the dispersion and caused a remarkable decrease in its power law index. Microstructures of nanofluids strongly depended on the dispersant chemistry used to stabilize the particles, and high temperature may cause dispersant failure. Mechanical methods for dispersing the particles affected the geometry of the nanoparticles and therefore the rheological properties of the nanofluids. In the creep recovery tests, the compliance of graphite nanofluids quickly returned to zero when the stress was removed, while nanotube dispersion with high nanotube loading showed an elastic response during recovery. These results suggest that the microstructure in the dispersions is affected by nanoparticle morphology, dispersant chemistry, and shear stress.
含有纳米颗粒的分散体（纳米流体）是具有独特性质的混合物，其传输性质取决于纳米颗粒的三维网络或微观结构，这会受到包括剪切应力、颗粒负载和温度等各种因素的影响。在本研究中，我们研究了含有两种不同碳形态的分散体的流变行为：多壁碳纳米管（长径比L/D = 30的棒状纳米颗粒）和石墨颗粒（长径比L/D = 0.025的盘状纳米颗粒）。在稳态剪切测量中，所有纳米流体均表现出剪切变稀行为，且含有纳米管的纳米流体的幂律指数低于石墨分散体。剪切应力破坏了微观结构网络，并使分散体中的棒状和盘状纳米颗粒定向排列。石墨纳米流体中存在适量的纳米管会影响分散体的微观结构，并导致其幂律指数显著降低。纳米流体的微观结构强烈依赖于用于稳定颗粒的分散剂化学性质，高温可能导致分散剂失效。分散颗粒的机械方法会影响纳米颗粒的几何形状，从而影响纳米流体的流变性质。在蠕变恢复测试中，去除应力后，石墨纳米流体的柔量迅速恢复到零，而高纳米管负载的纳米管分散体在恢复过程中表现出弹性响应。这些结果表明，分散体中的微观结构受纳米颗粒形态、分散剂化学性质和剪切应力的影响。
