Daniel Susan, Sircar Sanjoy, Gliem Jill, Chaudhury Manoj K
Department of Chemical Engineering, Lehigh University, Bethlehem, Pennsylvania 18015, USA.
Langmuir. 2004 May 11;20(10):4085-92. doi: 10.1021/la036221a.
The motions of liquid drops of various surface tensions and viscosities were investigated on a solid substrate possessing a gradient of wettability. A drop of any size moves spontaneously on such a surface when the contact angle hysteresis is negligible; but it has to be larger than a critical size in order to move on a hysteretic surface. The hysteresis can, however, be reduced or eliminated with vibration that allows the drop to sample various metastable states, thereby setting it to the path of global energy minima. Significant amplification of velocity is observed with the frequency of forcing vibration matching the natural harmonics of drop oscillation. It is suggested that the main cause for velocity amplification is related to resonant shape fluctuation, which can be illustrated by periodically deforming and relaxing the drop at low frequencies.
在具有润湿性梯度的固体基底上，研究了具有不同表面张力和粘度的液滴的运动。当接触角滞后可忽略不计时，任何尺寸的液滴都会在这样的表面上自发移动；但在具有滞后性的表面上移动时，液滴必须大于临界尺寸。然而，通过振动可以减小或消除滞后现象，振动使液滴能够采样各种亚稳态，从而使其沿着全局能量最小值的路径移动。当强迫振动频率与液滴振荡的自然谐波相匹配时，观察到速度有显著放大。有人认为，速度放大的主要原因与共振形状波动有关，这可以通过在低频下使液滴周期性地变形和松弛来说明。
