水滴与聚氧化乙烯液滴撞击荷叶表面的实验对比分析

为探究荷叶表面的液滴撞击行为规律，本文利用高速摄像机以14000帧/秒的帧率分别记录水滴和4种不同相对分子质量的聚氧化乙烯（polyethylene oxide，PEO）水溶液液滴竖直撞击荷叶表面的动力过程，其撞击速度为0.3~3m/s。实验结果表明，水滴与低相对分子质量（5×10⁴）的PEO液滴撞击荷叶表面的行为现象相似，两者随撞击速度增加依次有规则反弹、向上发射卫星液滴、不规则反弹（或部分反弹）、液滴破碎和液指断裂分离小液滴等现象发生，但水滴的接触时间更短，最大铺展系数也更小。中等相对分子质量（3×10⁵）PEO液滴在低速和高速撞击时分别为振荡弹起模态和振荡模态，临界速度为1.13m/s。高相对分子质量（1×10⁶、4×10⁶）的PEO液滴，其高分子长链与表面交互作用显著增强，表现出很强的黏性，撞击后反弹完全被抑制，均黏附沉积于荷叶表面；液滴发生沉积的临界Oh数为0.0544，且Oh数越大，液滴越难发生反弹。速度一定时，相对分子质量3×10⁵以上的3种PEO液滴的最大铺展系数均小于水滴；三者的上升系数随速度增加先减小后保持基本稳定或略微增加。

Comparative experiments and analysis of water droplet and PEO droplet impacting on the surface of lotus leaf

In order to investigate the law of behavior that liquid droplets impact on the surface of the lotus leaf, a high-speed camera was used to record water droplets and four kinds of polyethylene oxide (PEO) aqueous solution with different molecular weights vertically hitting the surface of the lotus leaf at a frame rate of 14000fps. During the dynamic process, the impact velocity ranged from 0.3m/s to 3m/s. The experimental results showed that the behavior of water droplets and PEO droplets with low molecular weight (50000) impacting the surface of the lotus leaf was similar. The two kinds of droplets both successively rebounded regularly, launched satellite droplets upward, rebounded irregularly (or partial rebounded), droplet breakage and liquid finger breakage to separate small droplets as the impact speed increased, but the contact time of water droplets was shorter and the maximum spreading coefficient was also smaller. The PEO droplets with medium relative molecular weights (300000) had an oscillating bounce mode and an oscillating mode when respectively impacted at low and high speeds, and its critical velocity was at 1.13m/s. The interaction between long polymer chains in PEO droplets with high molecular weight (1million, 4million) having strong viscosity and the surface was significantly enhanced. The rebound after impact was completely inhibited and all adhered and deposited on the surface of the lotus leaf. The critical Oh number for droplet deposition was 0.0544, and the larger the Oh number, the harder the droplet rebounded. When the speed was constant, the maximum spreading coefficients of the three kinds of PEO droplets with a relative molecular weight of more than 300000 were smaller than that of water droplets. The rising coefficients of the three kinds of PEO droplets first decreased with the increase of speed and then remained basically stable or slightly increase.