Department of Chemical and Materials Engineering, University of Alberta , Edmonton, Alberta, T6G 1H9, Canada.
Langmuir. 2018 Jan 23;34(3):729-738. doi: 10.1021/acs.langmuir.7b02693. Epub 2017 Oct 31.
Surface interactions involving deformable air bubbles have attracted tremendous interest in a wide range of engineering applications, such as mineral flotation and bitumen extraction. In this work, for the first time, the interaction forces between air bubbles and bitumen surfaces in complex aqueous media of varying pH, salinity, and salts were directly measured using a bubble probe atomic force microscope (AFM) technique. The AFM topographic imaging reveals that bitumen surface tends to be rougher and form distinct domains at high NaCl concentration or under strongly alkaline environment. The force measurements demonstrate the critical role of ionic strength and solution pH in bubble-bitumen interaction and attachment, which could be well described by a theoretical model based on Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. In 1 mM NaCl, the electrical double layer (EDL) repulsion inhibited bubble-bitumen attachment, and such a repulsive effect could be further strengthened with increasing solution pH. In 500 mM NaCl, the hydrophobic attraction could lead to bubble-bitumen attachment, while a high solution pH could weaken the hydrophobic interaction. The addition of calcium ion in 500 mM NaCl could enhance the hydrophobic interaction and facilitate the bubble-bitumen attachment, most likely attributed to the bridging effect between calcium ions and the functional groups (e.g., carboxyl group) of interface-active molecules on bitumen surfaces, thus leading to higher surface roughness and hydrophobic moieties/aggregates on bitumen as confirmed by AFM imaging. Our results provide quantitative information on the interaction mechanism between air bubbles and bitumen surfaces in complex aqueous solutions at the nanoscale, which has useful implications to many related interfacial interactions in industrial processes such as oil production, oil-water separation, and wastewater treatment.
在广泛的工程应用中，如矿物浮选和沥青提取，涉及可变形气泡的表面相互作用引起了极大的关注。在这项工作中，首次使用气泡探针原子力显微镜（AFM）技术直接测量了复杂水介质中气泡与沥青表面之间的相互作用力，该水介质的 pH 值、盐度和盐的变化。AFM 形貌成像表明，在高 NaCl 浓度或强碱性环境下，沥青表面趋于更粗糙并形成明显的畴。力测量表明离子强度和溶液 pH 值在气泡-沥青相互作用和附着中起着关键作用，这可以通过基于雷诺润滑理论和包括非定域压力影响的增强 Young-Laplace 方程的理论模型很好地描述。在 1 mM NaCl 中，双电层（EDL）排斥抑制了气泡-沥青附着，并且这种排斥效应可以随着溶液 pH 值的增加而进一步增强。在 500 mM NaCl 中，疏水力可导致气泡-沥青附着，而高溶液 pH 值可削弱疏水力。在 500 mM NaCl 中添加钙离子可以增强疏水力并促进气泡-沥青附着，这很可能归因于钙离子与界面活性分子在沥青表面上的官能团（例如羧基）之间的桥接效应，从而导致沥青表面的更高表面粗糙度和疏水性部分/聚集体，这通过 AFM 成像得到证实。我们的结果提供了在纳米尺度下复杂水溶液中气泡与沥青表面之间相互作用机制的定量信息，这对许多相关的界面相互作用在工业过程中具有有用的意义，如采油、油水分离和废水处理。
