Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt, Petersenstrasse 22, D-64287 Darmstadt, Germany.
Langmuir. 2013 Aug 6;29(31):9770-82. doi: 10.1021/la401655h. Epub 2013 Jul 25.
Molecular dynamics simulations of Lennard-Jones particles have been performed to study the evaporation behavior of nanodroplets on heated substrates. The influence of the liquid-substrate interaction strength on the evaporation properties was addressed. Our results show that, during the temperature-raising evaporation, the gas is always hotter than the droplet. In contrast to the usual experimental conditions, the droplet sizes in our simulations are in the nanometer scale range and the substrates are ideally smooth and chemically homogeneous. As a result, no pinning was observed in our simulations for substrates denoted either hydrophilic (contact angle θ < 90°) or hydrophobic (contact angle θ > 90°). The evaporative mass flux is stronger with increasing hydrophilicity of the substrate because the heat transfer from the substrate to the droplet is more efficient for stronger attraction between the solid and the droplet. Evaporation and heat transfer to the gas phase occur preferentially in the vicinity of the three-phase contact line in the hydrophilic system. However, in the case of a hydrophobic substrate, there is no preferential location for mass and heat fluxes. During the whole evaporation process, no pure behavior according to either the constant-angle or the constant-radius model was found; both the contact angle and contact radius decrease for the droplets on hydrophilic and hydrophobic substrates alike.
已对 Lennard-Jones 粒子进行分子动力学模拟，以研究加热基底上纳米液滴的蒸发行为。研究了液体-基底相互作用强度对蒸发特性的影响。研究结果表明，在升温蒸发过程中，气体始终比液滴热。与通常的实验条件不同，我们模拟中的液滴尺寸在纳米尺度范围内，基底是理想的光滑且化学均匀的。因此，对于我们模拟中的亲水（接触角θ<90°）或疏水（接触角θ>90°）基底，没有观察到钉扎现象。由于固体和液滴之间的吸引力更强，基底的亲水性越强，从基底到液滴的热传递就越有效，蒸发的质量通量就越强。在亲水体系中，蒸发和向气相的传热优先发生在三相接触线附近。然而，在疏水基底的情况下，质量和热通量没有优先位置。在整个蒸发过程中，没有发现符合恒角或恒半径模型的纯行为；亲水和疏水基底上的液滴的接触角和接触半径都减小了。
