振动固着液滴定向运动的定量研究
Directional motion of vibrated sessile drops : a quantitative study
摘要：
基片的倾斜机械振动可以诱导固着液滴的定向运动。如前所述，\cite{Brunet07,Brunet09,Noblin09}证明，机械振动引起液滴变形，其结合了轴对称和反对称模式。在本文中，我们建立定量的趋势，从实验中进行的参数范围很大，即振幅$A$和频率$f$的强制，液体粘度$η$和基板和强制轴之间的角度$α$。这些实验是在弱钉扎衬底上进行的。对于大多数参数集，平均速度$<v>$随$A$线性增长。我们提取的流动性，定义为$s=\frac{Δ<v>}{ΔA}$。研究发现，$s$在第一轴对称模态$f_p$的共振频率附近有一个尖锐的极大值。$s$值在低于50 cSt时几乎不依赖于$η$，而$s$在$η$较高时显著降低。此外，它被发现，对于特殊的参数集，特别是与$f$足够远的$f_p$，液滴在相反的方向移动。最后，我们画出了$<v>$和一个振荡周期内液滴两侧动态接触角的平均值之间的关系。
英文摘要：
The directional motion of sessile drops can be induced by slanted mechanical vibrations of the substrate. As previously evidenced \cite{Brunet07,Brunet09,Noblin09}, the mechanical vibrations induce drop deformations which combine axisymmetric and antisymmetric modes. In this paper, we establish quantitative trends from experiments conducted within a large range of parameters, namely the amplitude $A$ and frequency $f$ of the forcing, the liquid viscosity $η$ and the angle between the substrate and the forcing axis $α$. These experiments are carried out on weak-pinning substrates. For most parameters sets, the averaged velocity $<v>$ grows linearly with $A$. We extract the mobility, defined as $s=\frac{Δ<v>}{ΔA}$. It is found that $s$ can show a sharp maximal value close to the resonance frequency of the first axisymmetric mode $f_p$. The value of $s$ tends to be almost independent on $η$ below 50 cSt, while $s$ decreases significantly for higher $η$. Also, it is found that for peculiar sets of parameters, particularly with $f$ far enough from $f_p$, the drop moves in the reverse direction. Finally, we draw a relationship between $<v>$ and the averaged values of the dynamical contact angles at both sides of the drop over one period of oscillation.
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