Department of Crop and Soil Sciences, Washington State University, Pullman, Washington 99164, United States.
Langmuir. 2011 Aug 16;27(16):9985-93. doi: 10.1021/la201840q. Epub 2011 Jul 15.
Moving air-water interfaces can detach colloidal particles from stationary surfaces. The objective of this study was to quantify the effects of advancing and receding air-water interfaces on colloid detachment as a function of interface velocity. We deposited fluorescent, negatively charged, carboxylate-modified polystyrene colloids (diameter of 1 μm) into a cylindrical glass channel. The colloids were hydrophilic with an advancing air-water contact angle of 60° and a receding contact angle of 40°. After colloid deposition, two air bubbles were sequentially introduced into the glass channel and passed through the channel at different velocities (0.5, 7.7, 72, 982, and 10,800 cm/h). The passage of the bubbles represented a sequence of receding and advancing air-water interfaces. Colloids remaining in the glass channel after each interface passage were visualized with confocal microscopy and quantified by image analysis. The advancing air-water interface was significantly more effective in detaching colloids from the glass surface than the receding interface. Most of the colloids were detached during the first passage of the advancing air-water interface, while the subsequent interface passages did not remove significant amounts of colloids. Forces acting on the colloids calculated from theory corroborate our experimental results, and confirm that the detachment forces (surface tension forces) during the advancing air-water interface movement were stronger than during the receding movement. Theory indicates that, for hydrophilic colloids, the advancing interface movement generally exerts a stronger detachment force than the receding, except when the hysteresis of the colloid-air-water contact angle is small and that of the channel-air-water contact angle is large.
运动的气-水界面能够使胶体颗粒从静止表面脱离。本研究的目的是定量研究作为界面速度函数的前进和后退气-水界面对胶体脱离的影响。我们将带负电荷的羧基化修饰的荧光聚苯乙烯胶体（直径 1μm）沉积到圆柱形玻璃通道中。胶体具有亲水性，前进气-水接触角为 60°，后退接触角为 40°。胶体沉积后，两个气泡依次被引入玻璃通道，并以不同的速度（0.5、7.7、72、982 和 10800cm/h）通过通道。气泡的通过代表了后退和前进气-水界面的连续序列。通过共聚焦显微镜观察每个界面通过后留在玻璃通道中的胶体，并通过图像分析进行量化。前进气-水界面从玻璃表面脱离胶体的效果明显优于后退界面。大多数胶体在前进气-水界面的第一次通过中就被脱离，而随后的界面通过不会去除大量的胶体。从理论上计算的作用在胶体上的力证实了我们的实验结果，并确认在前进气-水界面运动过程中，脱离力（表面张力力）比后退运动过程中的更强。理论表明，对于亲水胶体，前进界面运动通常会产生比后退运动更强的脱离力，除非胶体-气-水接触角的滞后很小而通道-气-水接触角的滞后很大。
