Probing the Interaction Mechanism between Air Bubbles and Bitumen Surfaces in Aqueous Media Using Bubble Probe Atomic Force Microscopy

Abstract

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.

Anisotropic Polymer Adsorption on Molybdenite Basal and Edge Surfaces and Interaction Mechanism With Air Bubbles

“…The bubble-mineral attachment is governed by the combined influence of hydrodynamic and surface interactions (Xie et al, 2015, 2017a). The particle size can affect the hydrodynamic force, which will influence the bubble-mineral attachment.…”

“…Apparently, the exploit of polymer coated AFM probe can provide the comparable information on the polymer adsorption on different surfaces, but the adsorption capability of polymers cannot be directly and quantitatively provided. The bubble/drop probe AFM technique has also been developed and applied to study the interaction mechanisms involving deformable gas bubbles and emulsion drops, enabling the precise quantification of surface forces at air/water and oil/water interfaces with sub-nN resolution (Manor et al, 2008; Chan et al, 2011; Tabor et al, 2011; Shi et al, 2014a,b, 2016a,b, 2017; Xie et al, 2015, 2017a,b,d; Cui et al, 2016, 2017; Rocha et al, 2016). Very recently, the effect of aqueous conditions (e.g., pH, salinity and salts) on the interaction forces between air bubble and bitumen surface was quantitatively measured, and the evolution of confined thin water film drainage process was successfully analyzed using the theoretical model based on the Reynolds lubrication theory and augmented Young-Laplace equation (Xie et al, 2017d).…”

“…Very recently, the effect of aqueous conditions (e.g., pH, salinity and salts) on the interaction forces between air bubble and bitumen surface was quantitatively measured, and the evolution of confined thin water film drainage process was successfully analyzed using the theoretical model based on the Reynolds lubrication theory and augmented Young-Laplace equation (Xie et al, 2017d). It was found that the complex aqueous media effectively affected the bubble-surface attachment behaviors by mediating the electrical double layer (EDL) repulsion and hydrophobic attraction (Xie et al, 2017a). The bubble probe AFM technique coupled with other complementary surface analytic tools enables the investigation of the anisotropic adsorption and associated interaction mechanisms on MoS 2 basal and edge planes.…”

Investigation of the Stability of Liquid and Air Films by Synchronized Tri-Wavelength Reflection Interferometry Microscope

“…For interactions between two bubbles, the air bubble on the upper plate was created using a droplet transfer method. 54 In using this method, an air bubble was transferred from a mildly hydrophobized quartz plate to the upper hydrophobic quartz plate in water. The three-phase contact line for the air bubbles was assumed to be fixed with an unperturbed contact angle of 90 o .…”

“…Likewise, Ducker et al changed the relative positions of the air bubble and the solid surface and also were able to measure the interaction in the air bubble-mineral system 53 . Figure 2.9 Schematic of the AFM to investigate the bubble-particle attachment 54 , reprinted with permission.…”