Nam Youngsuk, Seo Donghyun, Lee Choongyeop, Shin Seungwon
Kyung Hee University, Yongin, 446-701, Korea.
Soft Matter. 2015 Jan 7;11(1):154-60. doi: 10.1039/c4sm01647e.
We report our hydrodynamic and energy analyses of droplet coalescence on water repellent surfaces including hydrophobic, superhydrophobic and oil-infused superhydrophobic surfaces. The receding contact angle has significant effects on the contact line dynamics since the contact line dissipation was more significant during the receding mode than advancing. The contact line dynamics is modeled by the damped harmonic oscillation equation, which shows that the damping ratio and angular frequency of merged droplets decrease as the receding contact angle increases. The fast contact line relaxation and the resulting decrease in base area during coalescence were crucial to enhance the mobility of coalescing sessile droplets by releasing more surface energy with reducing dissipation loss. The superhydrophobic surface converts ∼42% of the released surface energy to the kinetic energy via coalescence before the merged droplet jumps away from the surface, while oil-infused superhydrophobic and hydrophobic surfaces convert ∼30% and ∼22%, respectively, for the corresponding time. This work clarifies the mechanisms of the contact line relaxation and energy conversion during the droplet coalescence on water repellent surfaces, and helps develop water repellent condensers.
我们报告了对疏水性表面（包括疏水、超疏水和注油超疏水表面）上液滴聚并的流体动力学和能量分析。后退接触角对接触线动力学有显著影响，因为在后退模式下接触线耗散比前进时更为显著。接触线动力学由阻尼简谐振动方程建模，该方程表明合并液滴的阻尼比和角频率随着后退接触角的增加而降低。快速的接触线松弛以及聚并过程中基底面积的减小对于通过减少耗散损失释放更多表面能来提高聚并静止液滴的流动性至关重要。在合并液滴从表面跳离之前，超疏水表面通过聚并将约42%的释放表面能转化为动能，而注油超疏水和疏水表面在相应时间分别转化约30%和22%。这项工作阐明了疏水性表面上液滴聚并过程中接触线松弛和能量转换的机制，并有助于开发疏水冷凝器。
