Homo- and hetero-interactions between air bubbles and oil droplets measured by atomic force microscopy

Mapping coalescence of micron-sized drops and bubbles

“…In this study, we examine equilibrium and dynamic interactions of both bubble and drop pairs. We initially focus on systems exhibiting DLVO forces, which have are prevalent in nature and have been well characterised in the literature for bubbles [28,68] and drops [25,33,35]. We also consider drops exhibiting (repulsive) steric forces [37] and also drops with (attractive) depletion forces [36,40].…”

“…There have also been more recent developments, including the integration of interferometry with AFM to probe a single bubble with a flat surface [29], larger length-scale systems that utilise bimorph cantilevers and a single drop or bubble in the integrated thin film drainage apparatus (ITFDA) [30], and cantilevered capillaries to examine the interaction of two drops [31]. The range of surface forces examined in these experiments include Derjaguin-Landau-Verwey-Overbeek (DLVO) forces (the addition of electrical double layer and van der Waals) [25,32,33], repulsive van der Waals forces [34,35], steric [36,37], structural [36,38,39], depletion [36,40], protein interactions [36,41] and hydrophobic forces [42]. Common surface forces and their corresponding pressure and energy definitions are given in Tables S1 & S2 in the Supplementary Information (SI).…”

Rate of Bubble Coalescence following Quasi-Static Approach: Screening and Neutralization of the Electric Double Layer

“…Air-bubble coalescence is frequently encountered in nature as well as in industry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 . In some cases, rapid coalescence is preferred, e.g.…”

“…Relatively slow bubble coalescence (seconds or minutes) in aqueous solutions containing certain concentrations of electrolytes, was apparently first observed in 1929 10 . This phenomenon has been widely discussed 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 , since it appears to be in qualitative contradiction to the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory 38 , which describes the stability of colloidal particles in a medium, by calculating the combined effects of van der Waals (vdW) attraction and electric double layer (EDL) repulsion between the particles. It predicts accelerated bubble coalescence in aqueous solutions of electrolytes compared with purified water.…”

“…Various electrolytes have been investigated over the years, using a variety of methods to study bubble coalescence behavior. Since bubble coalescence is actually a process of thin film rupture, it has been studied by methods that apply to either whole bubbles or isolated thin films: a bubble column 11 12 13 14 15 16 17 18 19 20 , pairs of bubbles 12 19 21 22 23 24 25 26 , bubbles rising to the interface 27 28 29 30 , a liquid thin-film between two gas-phases 31 32 33 , and two bubbles in Atomic Force Microscopy (AFM) 34 35 36 . These studies have revealed the effect of electrolyte type and concentration on the rate of bubble coalescence, mostly when the approach of the coalescing bubbles is dynamic (approach velocity higher than 10 μm/sec).…”