Laboratory for Optics and Applied Mechanics, Department of Mechanical & Aerospace Engineering, Monash University , Clayton, Victoria 3800, Australia.
Langmuir. 2013 Sep 17;29(37):11615-22. doi: 10.1021/la402020q. Epub 2013 Aug 30.
The rupture of a liquid bridge has many applications while the rupture of a gaseous bridge is gaining importance in the use of bubbles to affect the speed of liquid flow over surfaces. Here, comparative experiments were conducted for liquid and gaseous bridges dispensed at fixed volumes of 6 μL on silicone (hydrophobic) and silane coated glass (hydrophilic) surfaces and with the dispensing tip retracted at different speeds. With the liquid bridge, increasing the retracting speed left behind lower volumes on the substrate. The pinch off position and the contact line radius were factors that determined the volume. The bridge first entered into a receding state before being able to restore toward equilibrium in a relaxation process closer to rupture. On silicone the contact angle was able to undergo higher degrees of hysteresis with faster tip retraction speeds due to the lower free surface energy. With gaseous bridges, only a very small volume was left behind on the silane coated glass while the volume deposited on silicone could be tuned from almost none at low retraction speeds to virtually the entire gaseous volume bridge at high retraction speeds. The tip and neck distances from the substrate increased with tip speed until 0.5 mm/s on the silicone surface, but, beyond that, the position remained invariant until rupture. With the progress toward rupture for the gaseous bridge, the contact angle advanced rather than receded and there was no relaxation stage that brought the contact angle back toward equilibrium before rupture. Overall the gaseous bridges responded very differently to tip retraction than the liquid bridges.
液体桥的破裂有许多应用，而在利用气泡来影响液体在表面上的流动速度方面，气态桥的破裂正变得越来越重要。在这里，对在固定体积为 6 μL 的情况下分配在硅酮（疏水性）和硅烷涂层玻璃（亲水性）表面上的液体和气体桥进行了比较实验，并以不同速度缩回分配尖端。对于液体桥，增加缩回速度会在基板上留下较低的体积。夹断位置和接触线半径是决定体积的因素。桥首先进入后退状态，然后才能在更接近破裂的松弛过程中恢复到平衡状态。在硅酮上，由于较低的自由表面能，接触角能够在更快的尖端缩回速度下经历更高程度的滞后。对于气态桥，在硅烷涂层玻璃上只留下非常小的体积，而在硅酮上沉积的体积可以从低缩回速度下几乎没有到高缩回速度下几乎整个气态体积桥进行调节。尖端和颈部与基板的距离随尖端速度增加，直到硅酮表面上的 0.5 mm/s，但超过该速度后，位置保持不变，直到破裂。对于气态桥的破裂过程，接触角前进而不是后退，并且在破裂之前没有使接触角回到平衡的松弛阶段。总体而言，气态桥对尖端缩回的响应与液体桥非常不同。
