Thermophoresis of Janus particles at large Knudsen numbers
Thermophoresis of Janus particles at large Knudsen numbers
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DOI：
10.1103/physrevfluids.3.094202
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发表时间：
2018-09-12
影响因子：
2.7
通讯作者：
Hardt, Steffen
中科院分区：
文献类型：
--
作者：
Baier, Tobias;Tiwari, Sudarshan;Hardt, Steffen
计算了Janus球在有温度梯度的稀薄气体中运动时所受的力和力矩。考虑了大Knudsen数区域，在不同温度下，碰撞气体分子的动量由Chapman-Enskog分布或相对平行板之间的二元Maxwell分布获得。Janus粒子表面的反射特性由每个半球上具有恒定但不同值的调节系数来表征。结果表明，Janus粒子的择优取向使得容纳系数较大的半球指向较低的温度。计算了颗粒的热湿速度，研究了热湿运动对颗粒取向力矩大小的影响。分析计算得到了直接模拟蒙特卡罗结果的支持，从而将研究范围扩展到较小的克努森数。这一结果揭示了纳米颗粒从气相定向沉积到冷表面的效率。
The force and torque on a Janus sphere moving in a rarefied gas with a thermal gradient are calculated. The regime of large Knudsen number is considered, with the momenta of impinging gas molecules either obtained from a Chapman-Enskog distribution or from a binary Maxwellian distribution between two opposing parallel plates at different temperature. The reflection properties at the surface of the Janus particle are characterized by accommodation coefficients having constant but dissimilar values on each hemisphere. It is shown that the Janus particle preferentially orients such that the hemisphere with a larger accommodation coefficient points toward the lower temperature. The thermophoretic velocity of the particle is computed, and the influence of the thermophoretic motion on the magnitude of the torque responsible for the particle orientation is studied. The analytical calculations are supported by direct simulation Monte Carlo results, extending the scope of the study toward smaller Knudsen numbers. The results shed light on the efficiency of oriented deposition of nanoparticles from the gas phase onto a cold surface.