Formation and influence of the dynamic adsorption layer on kinetics of the rising bubble collisions with solution/gas and solution/solid interfaces

Ultraviolet-Driven Janus Foams with Wetting Gradients: Unidirectional Penetration Control for Underwater Bubbles

Understanding the behavior of underwater bubbles and enabling their effective manipulation is important for bubble capture, collection, and transport. Here, to discuss the underwater permeation behavior of bubbles and critical influencing parameters in this process, the copper foams with tunable wettability were fabricated by utilizing the light-stimulated wettability response of TiO₂. The Janus copper foams had different wettability gradients from superhydrophobic/hydrophobic to superhydrophobic/hydrophilic after UV irradiation at different times, and the bubbles on the surfaces showed distinctly diverse penetration behaviors. In particular, the constructed superhydrophobic/hydrophilic surfaces showed more difficult to achieve bubble penetration than the fully superhydrophobic, superhydrophobic/hydrophobic surface. It was found that the wetting states of the foams exposed to different irradiation times underwater plays a crucial role in the bubble penetration behavior. In other words, the difficulty of bubble penetration depends on the difficulty of bubble transition from gas-liquid contact to gas-solid contact. This facile and low-cost fabrication approach for Janus foams provided a valuable approach to understand the penetration behaviors of underwater bubbles, which is significant for expanding potential applications in bubble capture, bubble transport, and control of unstable gas reactions in underwater conditions.

Stacking polymer microspheres matrix: a facile, practical, and energy-saving strategy for suppression of acid mist

The electroplating, electrolysis, and pickling industrial processes would generate numerous gas pollutes, acid mist, which could not be essentially diminished due to its synthesis mechanism and cause gaseous environmental pollution, equipment corrosion, and endanger workers' health. In this study, a facile, practical, and energy-saving acid mist suppression system was constructed by introducing a stacking microsphere matrix as a floating porous phase on the acid solution and not causing secondary pollution. The mechanism of this green acid mist suppression strategy mainly focused on size-selective blocking of acid mist droplets by dense stacking microsphere layer and dissipation of floating kinetic energy of bubbles in the acid mist. The factors relating to the matrix's microstructure, the particle size of microspheres, the combination of the complex particles with a wide range of particle sizes, and the thickness of the matrix on the acid mist suppression were explored. It found that the matrix constituted of a medium-sized polymer sphere (1.075 ± 0.175 mm) presents a better appearance in the acid mist suppression. When the thickness of this matrix reached 15 mm, its acid mist efficiency also came up to 100%, totally blocking the acid mist. Meanwhile, complex particles with different particle sizes and PMMA porous blocks are beneficial for suppressing acid mist. Herein, this research opened up a green and effective strategy for regulating this hazardous gas pollute, acid mist.

Comparison and Mechanism Analysis of Three-Phase Contact Formation onto Hydrophilic/Hydrophobic Mineral Surfaces in the Presence of Cationic/Anionic Surfactants during Flotation Process

This article presents the dynamic process of the three-phase contact (TPC) formation by colliding bubbles onto muscovite and talc surfaces in water and two types of solutions including cationic CTAC surfactant (cetyltrimethyl ammoniumchloride) and anionic NaOL surfactant (sodium oleate). The TPC formation process was observed through the high-speed camera between bubbles and layered silicate minerals (hydrophilic muscovite and hydrophobic talc). It was found that the rupture of the liquid film between the bubbles and the mineral surface is a prerequisite for TPC formation. In the case of muscovite, TPC was formed only with cationic CTAC, and as the surfactant concentration increased, the time needed for TPC formation was shortened. Due to electrostatic repulsion, TPC did not occur in water and NaOL. However, for talc, TPC occurred both in water and in surfactant solutions. In contrast to muscovite, the time of TPC formation on the talc surface was prolonged with the increase in the surfactant concentration. It was concluded that hydrophobic attraction and electrostatic attraction between mineral surfaces and bubbles can significantly promote the localized foam film rupture, which was the main reason for the TPC appearance in water and surfactants. For the hydrophilic muscovite, CTAC adsorption improved the surface hydrophobicity; I3/I1 in fluorescence spectroscopy increased, and the micro-polarity faded, making TPC formation need more time. However, for the natural hydrophobic talc, the increasing surfactant adsorption decreased I3/I1 values and enhanced the local micro-polarity, causing the extension of time for TPC. Therefore, TPC formation for different minerals resulted from different reasons.

β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 4. Impact on the Stability of Foam Films and Foams

The complexity and high sensitivity of proteins to environmental factors give rise to a multitude of variables, which affect the stabilization mechanisms in protein foams. Interfacial and foaming properties of proteins have been widely studied, but the reported unique effect of pH, which can be of great interest to applications, has been investigated to a lesser extent. In this paper, we focus on the impact of pH on the stability of black foam films and corresponding foams obtained from solutions of a model globular protein—the whey β-lactoglobulin (BLG). Foam stability was analyzed utilizing three characteristic parameters (deviation time, transition time and half-lifetime) for monitoring the foam decay, while foam film stability was measured in terms of the critical disjoining pressure of film rupture. We attempt to explain correlations between the macroscopic properties of a foam system and those of its major building blocks (foam films and interfaces), and thus, to identify structure-property relationships in foam. Good correlations were found between the stabilities of black foam films and foams, while relations to the properties of adsorption layers appeared to be intricate. That is because pH-dependent interfacial properties of proteins usually exhibit an extremum around the isoelectric point (pI), but the stability of BLG foam films increases with increasing pH (3–7), which is well reflected in the foam stability. We discuss the possible reasons behind these intriguingly different behaviors on the basis of pH-induced changes in the molecular properties of BLG, which seem to be determining the mechanism of film rupture at the critical disjoining pressure.

On importance of external conditions and properties of the interacting phases in formation and stability of symmetrical and unsymmetrical liquid films

Importance of external conditions and properties of phases creating liquid films, in outcome of the air bubble collisions with liquid/air and liquid/solids interfaces in clean water and in liquid solutions, is critically reviewed. The review is focussed on initial stages of the liquid films formation by bubbles colliding with interfaces, as well as, on analysis of the most important factors responsible for the collision's outcome, that is, either the rapid bubble bouncing or formation of the symmetrical or unsymmetrical liquid films and their thinning to the critical rupture thicknesses. Data on formation of liquid films under dynamic conditions, both in pure liquids and solutions of electrolytes and various surface-active substances, are reviewed and importance of hydrodynamic boundary conditions at interacting interfaces for energy balance in the system is discussed. It is shown that the liquid films stability, which in stagnant systems are directly determined by properties of the liquid/gas and liquid/solid interfaces, can be quite different in dynamic environment. A mechanism of the bubble bouncing from various interfaces in terms of interplay between energy exchange and kinetics of liquid film drainage is analyzed. It is shown that this mechanism is universal and irrelevant on the nature of interacting phases. Moreover, mechanisms responsible for wetting (unsymmetrical) film stability under dynamic conditions are discussed in light of the most recent studies, showing a crucial role of electrolyte, kind and concentration of surface-active substances, electrical surface charge, hydrophilic/hydrophobic properties of solids and presence of air entrapped (nano- and/or micro-bubbles) at surfaces of highly hydrophobic solids in the liquid films rupture.

Initial degree of detaching bubble adsorption coverage and the kinetics of dynamic adsorption layer formation

We show, for the first time, the influence of the initial adsorption coverage over a bubble on the kinetics of dynamic adsorption layer formation.

"Bubble-on-demand" generator with precise adsorption time control

The paper presents the principles of our new single bubble generator, which allows a precise control of bubble formation in pure liquids and surfactant solutions, i.e., their detachment frequency and the adsorption time at their motionless surface. We show that the bubbles with equilibrium size can be produced at the capillaries of various orifice diameters (0.022-0.128 mm) on demand and with outstanding reproducibility. Moreover, it is shown that a fully automatized and programmable bubble trap, synchronized with bubble detachment frequency, can be used to (i) control the radius of the released bubble and (ii) precisely adjust the initial adsorption coverage over the surface of detaching bubble, and hence to study the influence of adsorption coverage degree on kinetics of dynamic adsorption layer formation at the rising bubble surface.

Variation of Local Surface Properties of an Air Bubble in Water Caused by Its Interaction with Another Surface

Surface and hydrodynamic forces acting between an air bubble and a flat mica surface in surfactant-free water and in 1 mM KCl solution have been investigated by observing film drainage using a modified surface force apparatus (SFA). The bubble shapes observed with the SFA are compared to theoretical profiles computed from a model that considers hydrodynamic interactions, surface curvature, and disjoining pressure arising from electrical double layer and van der Waals interactions. It is shown that the bubble experiences double-layer forces, and a final equilibrium wetting film between the bubble and mica surfaces is formed by van der Waals repulsion. However, comparison with the theoretical model reveals that the double-layer forces are not simply a function of surface separation. Rather, they appear to be changed by one of more of the following: the bubble's dynamic deformation, its proximity to another surface, and/or hydrodynamic flow in the aqueous film that separate them. The same comments apply to the hydrodynamic mobility or immobility of the air-water interface. Together the results show that the bubble's surface is "soft" in two senses: in addition to its well-known deformability, its local properties are affected by weak external forces, in this case the electrical double-layer interactions with a nearby surface and hydrodynamic flow in the neighboring aqueous phase.