Department of Applied Physics, University of Granada, Granada, Spain.
Langmuir. 2011 Jul 19;27(14):8748-52. doi: 10.1021/la2010858. Epub 2011 Jun 24.
Currently, there is no conclusive evidence regarding the global equilibrium condition of vibrated drops. However, it is well-known that vibration of sessile drops effectively reduces the contact angle hysteresis. In this work, applying a recent methodology for evaluating the most-stable contact angle, we examined the impact of the type of excitation signal (random signal versus periodical signal) on the values of the most-stable contact angle for polymer surfaces. Using harmonic signals, the oscillation frequency affected the postvibration contact angle. Instead, the white noise signal enabled sessile drops to relax regardless of their initial configuration. In spite of that, the values of most-stable contact angle obtained with different signals mostly agreed. We concluded that not only the amount of relaxation can be important for relaxing a sessile drop but also the rate of relaxation. Together with receding contact angle, most-stable contact angle, measured with the proposed methodology, was able to capture the thermodynamic changes of "wetted" polymer surfaces.
目前，关于振动液滴的全球平衡条件还没有确凿的证据。然而，众所周知，振动液滴可以有效地减少接触角滞后。在这项工作中，我们应用了一种评估最稳定接触角的新方法，研究了激励信号类型（随机信号与周期信号）对聚合物表面最稳定接触角值的影响。使用谐波信号时，振动频率会影响振动后的接触角。相反，白噪声信号可以使液滴松弛，而与初始状态无关。尽管如此，不同信号下获得的最稳定接触角值大多是一致的。我们得出结论，不仅松弛的量度对于松弛一个固着液滴很重要，而且松弛的速率也很重要。与后退接触角一样，用提出的方法测量的最稳定接触角能够捕捉到“润湿”聚合物表面的热力学变化。
