Daub Christopher D, Tafjord Joakim, Kjelstrup Signe, Bedeaux Dick, Bresme Fernando
Department of Chemistry, Norwegian University of Science and Technology (NTNU), Trondheim, NO-7491, Norway.
Department of Chemistry, Imperial College London, SW7 2AZ, London, UK and Department of Chemistry, Norwegian University of Science and Technology (NTNU), Trondheim, NO-7491, Norway.
Phys Chem Chem Phys. 2016 Apr 28;18(17):12213-20. doi: 10.1039/c6cp01231k.
We investigate, using non-equilibrium molecular dynamics simulations and theory, the response of molecular fluids confined in slit pores under the influence of a thermal gradient and/or an applied force. The applied force which has the same functional form as a gravitational force induces an inhomogeneous density in the confined fluid, which results in a net orientation of the molecules with respect to the direction of the force. The orientation is qualitatively similar to that induced by a thermal gradient. We find that the average degree of orientation is proportional to the density gradient of the fluid in the confined region and that the orientation increases with the magnitude of the force. The concurrent application of the external force and the thermal gradient allows us to disentangle the different mechanisms leading to the thermal orientation of molecular fluids. One mechanism is connected to the density variation of the fluid, while the second mechanism can be readily observed in molecular fluids consisting of molecules with mass or size asymmetry, even in the absence of a density gradient, hence it is connected to the application of the thermal gradient only.
我们运用非平衡分子动力学模拟和理论，研究了在热梯度和/或外力作用下，受限在狭缝孔隙中的分子流体的响应。与引力具有相同函数形式的外力会在受限流体中诱导出不均匀密度，这导致分子相对于力的方向产生净取向。这种取向在定性上与热梯度诱导的取向相似。我们发现，平均取向程度与受限区域内流体的密度梯度成正比，并且取向程度随力的大小增加而增大。外力和热梯度的同时施加使我们能够区分导致分子流体热取向的不同机制。一种机制与流体的密度变化有关，而第二种机制即使在没有密度梯度的情况下，也能在由具有质量或尺寸不对称性的分子组成的分子流体中轻易观察到，因此它仅与热梯度的作用有关。
