颗粒气泡黏附科学:基于AFM和DWFA的颗粒气泡间疏水作用力研究

Bubble-particle attachment science:study on hydrophobic force between bubble and particle based on AFM and DWFA

为探索颗粒气泡体系疏水力的长程及短程来源机制,分别采用原子力显微镜(AFM)和浮选动态润湿膜分析仪(DWFA)对气泡与同一疏水玻璃基板间的疏水力进行测试。AFM发现气泡与亲水性玻璃基板间的相互作用力为单调斥力作用,体系不存在诱发液膜失稳的引力作用项。疏水性颗粒气泡间的液膜是不稳定的,当AFM负载力到达19.3nN时,力曲线中观察到了明显的跳入黏附现象。疏水玻璃与气泡间的疏水力以3.50nm的衰减长度按单指数模型衰减,液膜在32.96nm临界破裂厚度处破裂。该疏水力倾向于一种短程力(<50nm),其源自界面的水分子重排熵效应。DWFA法同样发现亲水性玻璃基板与气泡间的液膜是稳定的,当总分离压力与气泡内部拉普拉斯压力相等时,液膜到达133nm的平衡膜厚度。疏水性玻璃基板与气泡间的液膜是不稳定的,液膜发生快速薄化并分别在185nm临界膜厚处破裂。对疏水力进行定量求解发现该力以47.30nm的衰减长度衰减,所获得的疏水力为一种长程作用力,该力源于固液界面纳米气泡空化效应。AFM和DWFA排液试验中所用的气泡尺寸分别为微米级及毫米级,疏水力受气泡本身的尺寸影响,与气泡表面的毛细波传播有关,在吸引力作用下大气泡表面会形成更强烈的毛细波震荡。由于疏水界面水分子的热力学不稳定性,这种界面波动会诱发疏水固液界面空化气泡的析出,增加了引力作用程。

To explore the origin mechanism of long-ranged and short-ranged hydrophobic force in bub-ble-particle system,atomic force microscopy (AFM) and flotation dynamic wetting film apparatus (DWFA) were used to measure the hydrophobic force between air bubble and the same hydrophobic glass substrate.AFM results showed that the force between hydrophilic glass substrate and bubble was always repulsive since the both van der Waals force and double layer force were repulsive.There was no attractive force triggering film rupture in the system.The film between hydrophobic glass and bubble was unstable.When 19.3 nN loading force was reached,a significant jump-into contact was observed in the force curves.The hydrophobic force was attenuated by a single exponential model with 3.50 nm decay length.Film ruptured at 32.96 nm critical thickness.This kind of hydrophobic force tented to be a short-ranged force,originated from the entropy effect due to the re-arrangement of interface water molecules.DWFA results also showed that the film between hydrophilic glass and bubble was thermostatically stable.133 nm equilibrium film thickness was reached when the total disjoining pressure was equal to the Laplace pressure inside air bubble.Also,the film between hydrophobic glass and bubble was unstable.The liquid film thinned rapidly and ruptured at the critical thickness of 185 nm.The decay length of hydrophobic force was 47.30 nm and was a kind of long-ranged force,originated from the nanobubble cavitation effect on solid-liquid interface.The bubble used in AFM and DWFA experiments was micro-meter and millimeter,respectively.The hydrophobic force was influenced by the bubble size and related with the capillary wave on bubble surface.Under the attraction force,more intensive interface wave was formed on the big bubble surface.Due to the thermodynamic instability of water molecules at hydrophobic interfaces,this kind of interface wave induced the precipitation of cavitation bubble on the hydrophobic interface and increased the range of hydrophobic force.