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中国物理学会期刊

超疏水表面液滴的振动特性及其与液滴体积的关系

CSTR: 32037.14.aps.70.20201771

Oscillation properties of water droplets on a superhydrophobic surface and their correlations with droplet volume

CSTR: 32037.14.aps.70.20201771
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  • 超疏水表面液滴的振动特性与接触线的移动、液滴体积、基底振幅等因素密切相关. 本文在基底振幅较小且恒定的条件下, 研究了超疏水表面液滴的共振振幅、模式区间、共振频率等振动特性及其与液滴体积(20—500 μL)的关系. 此外, 将基于一般性疏水表面建立的Noblin共振频率计算模型应用于超疏水表面, 并提出“虚驻点”的概念, 借此对模型进行了误差分析和修正. 研究表明: 1)共振时, 液滴高度变化率即比振幅随体积增大而增大, 随阶数增大而减小; 2)各模式区间的起止频率首尾相接, 其范围随体积增大而减小; 3)液滴体积越大, 共振频率越小, 随着阶数增大, 共振频率f与体积V的关系趋于f -V–0.4, 不同于一般性疏水表面上的f -V–0.5; 4)直接应用Noblin模型计算共振频率会产生较大误差, 主要原因在于液滴表面波波段数量统计存在较大偏差, 而修正后的模型可以准确计算超疏水表面大体积液滴的共振频率.

     

    In-depth understanding is limited to the oscillation properties of a droplet on a superhydrophobic surface, which are closely related to the contact line movement, droplet volume, and substrate amplitude, to name only a few factors. In the present work, we investigate the characteristics of droplet resonance amplitude, mode range, and resonance frequency, as well as their correlations with droplet volume (from 20 to 500 μL). In particular, the theoretical resonance frequency is mainly concerned and addressed. To this end, a model based on general hydrophobic surfaces proposed by Noblin et al. is employed, with its applicability to superhydrophobic surfaces examined. We propose a concept “virtual stationary point” for analyzing the errors from this model, with which we modify the model through using the correction coefficients. The main results are concluded as follows. 1) Under resonance, the change rate in droplet height rises with the increase of droplet volume and reduces with the increase of oscillation mode number. 2) Each number of oscillation mode corresponds to a frequency range, and the ends of adjacent mode ranges are connected to each other. These frequency ranges decrease with the increase of droplet volume. 3) Resonance frequency, f, decreases with the increase of droplet volume, V, and they are related approximated by f -V–0.4 under high mode numbers, which is different from f -V–0.5 as found on general hydrophobic surfaces. 4) Direct application of Noblin model to a superhydrophobic surface results in nonnegligible errors, because geometric characteristics in this case are different from those on a general hydrophobic surface, which leads to inaccuracy in counting the number of surface wave segments. In contrast, results from modified Noblin model accord well with experimental results.

     

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