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中文核心期刊

水滴在碳纳米管中的热泳特性研究

THERMOPHORESIS OF WATER DROPLETS IN CARBON NANOTUBES

  • 摘要: 基于分子动力学模拟方法,研究了温度梯度导致的碳纳米管中水滴的热泳驱动现象。当碳纳米管两端存在温差时,水滴总是沿着轴向由高温向低温方向运动。但是,水滴的布朗运动给热泳力的计算带来一定的困难,其热泳机制尚不明确。本文通过对水滴施加简谐回复力,提出基于管内水滴的受力平衡计算得到了水滴所受的热泳力。结果表明,随着组成水滴水分子数的增加,水滴与碳纳米管之间的相互作用能也逐渐增强,热泳力会增大;当碳纳米管的直径逐渐增大时,由于单位面积的水分子数增加,因而热泳力也会增大;当系统温度升高时,水分子更容易克服固-液界面的势垒而离开界面,界面疏水性增强,其热泳效应会减弱;对系统施加外加轴向电场,随着电场强度的增大,热泳效应显著增强,并且管内水分子偶极向量的方向会逐渐趋向与电场方向一致。揭示了水滴在碳纳米管中的热泳机理,有助于理解在纳米受限结构中固-液界面的热泳现象。

     

    Abstract: The thermophoresis of water droplets in carbon nanotubes is studied by using molecular dynamics (MD) simulations. Owing to the temperature gradient in the carbon nanotubes, the water droplets can move along the axial direction from high to low temperature. However, it is difficulty to calculate the thermophoretic forces on water droplets in carbon nanotubes owing to the Brownian motion of water droplets, and the mechanism of thermophoresis still unclear. In this paper, by imposing a harmonic force to the water droplet, the thermophoretic force acting on the water droplet can be obtained based on the balance between the thermophoretic force and the harmonic force. The results indicate that as the number of water molecules of the water droplets increases, the interaction energy between the water droplets and carbon nanotubes gradually strengthens, and the thermophoretic force increases. As the diameter of carbon nanotubes gradually increases, the thermophoretic force also increases due to the increase in the number of water molecules per unit area. As the system temperature increases, water molecules are more likely to overcome the potential barrier at the solid-liquid interface and detach from the interface, leading to enhanced interfacial hydrophobicity and a corresponding reduction in the thermophoretic effect. In addition, applying an external axial electric field to the system, as the electric field strength increases the thermophoretic effect significantly enhances, and the direction of the dipole vectors of the water molecules gradually be the same as the direction of electric field. This paper reveals the thermophoresis mechanism of water droplets in the carbon nanotubes, which helps to understand the thermophoresis phenomenon at the solid-liquid interface in nano-confined structures.

     

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