Electro-wetting of a nanoscale water droplet on a polar solid surface in electric field
Electro-wetting of a nanoscale water droplet on a polar solid surface in electric field
复制标题
电场中极性固体表面纳米级水滴的电润湿
DOI：
10.1039/c8cp00956b
复制
发表时间：
2018-05-07
影响因子：
3.3
通讯作者：
Li, Ben Q.
中科院分区：
文献类型：
--
作者：
Song, Fenhong;Ma, Long;Li, Ben Q.
采用分子动力学模拟方法研究了不同电场频率下纳米液滴在极性二氧化硅SAKI基片上的润湿特性。结果表明，外加电场对纳米液滴在极性SAKI衬底上的润湿有显著影响。在外加电场的作用下，液滴的扩散是不对称的，当电场为0.45V nm(-1)时，这种不对称达到最大值。对于1.0V nm(-1)的电场，即使在对称的平衡扩散态下，动态电润湿过程也经历了两个阶段。当前缘分子由于固体衬底的强烈吸引而落到固体表面时，A-B阶段突然发生。此外，在不同GHz频率范围的交变电场下，观察到随着电场频率的增加，扩散不对称性减弱，纳米水滴的形状在阈值频率以上变化很小。伴随着水滴形状的变化，由于电场诱导水分子重新排列，水分子的偶极取向发生了显著的变化，由无序分布变为有序分布。此外，与单个液滴相比，极性固体表面对水分子的重排有显著的影响。因此，水滴在二氧化硅固体表面的电润湿行为是由水、固体和电场之间的竞争分子间力决定的。
Molecular dynamics simulations were applied to study the wetting properties of nanoscale droplets on a polar silica saki substrate subjected to constant and alternative electric fields with various field frequencies. Results show that the external applied electric fields have significant effects on the wetting of the nanoscale droplet on a polar saki substrate. The droplet spreads asymmetrically under the effect of the external applied field, and this asymmetry culminates to the maximum when the electric field equals to 0.45 V nm(-1). For an electric field of 1.0 V nm(-1), the dynamic electro-wetting process undergoes two stages even with a symmetric equilibrium spreading state. The stage A-B transition happens suddenly when molecules on the leading edge drop onto the solid surface due to the strong attraction of the solid substrate. Furthermore, under the alternative electric field with a different GHz frequency range, it was observed that the spreading asymmetry was weakened by increasing the field frequency and the nanoscale water droplet shape changes very slightly above a threshold frequency. Accompanied by the shape variation of water droplets, the molecular dipole orientations of water molecules experience a remarkable change from a random disordered distribution to an ordered profile because of the realignment of water molecules induced by electric fields. In addition, the polar solid surface has significant effects on the rearrangement of water molecules compared with a single droplet. Thus, the electro-wetting behaviors of water droplets on a silica solid surface are determined by the competing intermolecular forces among water, solid and the electric field.