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arXiv 1608.08286cond-mat.soft
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线张力作用下球形空穴填充的自由能垒:对球形空穴超疏水表面Cassie态和Wenzel态间能垒的启示

Free-energy barrier of filling a spherical cavity in the presence of line tension: Implication to the energy barrier between the Cassie and Wenzel state on a superhydrophobic surface with spherical cavities

Masao Iwamatsu

摘要:

本文研究了具有不同润湿性内壁的球形空腔的自由能垒。透镜状液滴的形态和自由能由自由能的最小值确定。研究了线张力对自由能的影响。然后,从广义杨氏方程确定液滴的平衡接触角。通过增加球形腔内的液滴体积,液滴形态从具有$180^{\circ}$的平衡接触角的球形变为具有凸弯月面的透镜,其中发生形态完全干燥转变。通过进一步增加液滴体积,弯月面从凸形变为凹形。然后,具有凹弯月面的透镜状液滴在整个内壁上扩散,导致$0^{\circ}$的平衡接触角,从而留下球形气泡,在此发生形态学上的完全润湿转变。最后,整个空腔充满液体。自由能显示了从完全干燥到完全润湿的屏障作为液滴体积的函数,其对应于具有球形空腔的超疏水表面的Cassie和Wenzel状态之间的能量屏障。自由能最大值出现在液滴弯月面变平时,并由解析公式给出。线张力的影响由缩放的线张力表示,并且该影响在自由能最大值处最大。正的线张力增加了自由能最大值,从而增加了Cassie超疏水状态的稳定性,而负的线张力使超疏水状态不稳定。

英文摘要:

The free-energy barrier of filling a spherical cavity having an inner wall of various wettabiities is studied. The morphology and free energy of a lens-shaped droplet are determined from the minimum of the free energy. The effect of line tension on the free energy is also studied. Then, the equilibrium contact angle of the droplet is determined from the generalized Young's equation. By increasing the droplet volume within the spherical cavity, the droplet morphology changes from spherical with an equilibrium contact angle of $180^{\circ}$ to a lens with a convex meniscus, where the morphological complete drying transition occurs. By further increasing the droplet volume, the meniscus changes from convex to concave. Then, the lens-shaped droplet with concave meniscus spreads over the whole inner wall resulting in an equilibrium contact angle of $0^{\circ}$ to leave a spherical bubble, where the morphological complete wetting transition occurs. Finally, the whole cavity is filled with liquid. The free energy shows a barrier from complete drying to complete wetting as a function of droplet volume, which corresponds to the energy barrier between the Cassie and Wenzel state of the superhydrophobic surface with spherical cavities. The free-energy maximum occurs when the meniscus of the droplet becomes flat and it is given by an analytic formula. The effect of line tension is expressed by the scaled line tension, and this effect is largest at the free-energy maximum. The positive line tension increases the free-energy maximum, which thus, increases the stability of the Cassie superhydrophobic state, whereas the negative line tension destabilizes the superhydrophobic state.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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