Stability of Liquid Films Formed by a Single Bubble and Droplet at Liquid/Gas and Liquid/Liquid Interfaces in Bovine Serum Albumin Solutions.

Dorota Gawel,Jan Zawala

doi:10.1021/acsomega.1c02188

Abstract

The properties of thin liquid films are usually investigated under static conditions, isolated from external disturbances. Such studies provide vital information about the drainage mechanism of the thin liquid film, but the conditions of these measurements are vastly different from those that occur when a real dispersed system is created. In this paper, we present elaborated methodologies that allow qualitative and quantitative measurements of the stability of both the emulsion and foam films formed by a single bubble and droplet at liquid/gas and liquid/liquid interfaces, where the hydrodynamic factors are of crucial importance. The experiments were performed in a bovine serum albumin (BSA) solution at different pH values. The adsorption behavior of BSA under different pH conditions at the liquid/gas and liquid/liquid interface is described, and its implication for the single bubble/droplet motion and liquid film drainage is analyzed. The mechanism of thin-liquid-film stabilization by the BSA molecules is shown to be significantly different for the foam and emulsion films and depends significantly on the bubble history as well as the pH of the BSA solution. Additionally, the results obtained for BSA were compared to those acquired for a typical surface-active substance, sodium lauryl sulfate. The similarities and differences in the rising bubble/droplet dynamics (caused by different dynamic adsorption layer architectures) and foam and emulsion film stabilization by these two types of stabilizers under dynamic conditions are shown and discussed.

Highlights

Emulsions and foams represent a group of dispersed systems widely encountered in industry, technology, separation processes, and everyday products
The majority of studies on the properties of liquid films have been performed at a plane liquid/liquid interface under static conditions, where the liquid film was isolated from any external disturbances.[4−8] Studies conducted under such a regime are extremely important as they allow for the determination of the drainage kinetics of the thin liquid film and the characterization of intermolecular forces
In the case of surface-active substances, the terminal velocities presented in Figure 7 were averaged for all the aging times studied during the experiments

Summary

Introduction

Emulsions and foams represent a group of dispersed systems widely encountered in industry, technology, separation processes, and everyday products. There are many motions, disturbances, and various dynamic processes that lead to bubble/droplet collisions, bouncing, and energy dissipation Such dynamic conditions directly influence the drainage kinetics of the formed liquid films, which can be governed by motion-induced dynamic effects occurring at interacting interfaces (e.g., surface tension gradients). These dynamic effects act as “brakes” that slow down the process of liquid drainage to the critical thickness of rupture and prevent the process of coalescence of interacting droplets/ bubbles.[9] Under dynamic conditions, hydrodynamic factors such as dynamic adsorption layer and interface area changes determine the ability of thin liquid films to prevent initial disturbances and survive until static conditions are established, in which equilibrium thickness is reached and a liquid film can exist for a long period of time.[10−13]

Methods

Results

Conclusion