Hydrophobicity of Benzene-Based Surfactants and Its Effect on Bubble Coalescence Inhibition.

Bubble coalescence plays a critical role in optimizing biological and industrial processes, impacting efficiency in areas such as fermentation, wastewater treatment, and foaming control. While the relationship between chemical structure and bubble coalescence has been thoroughly explored for inorganic ions, limited data exist on organic ions and surfactants, despite their widespread use in these industries. This study addresses this gap by investigating the effects of surfactant hydrophobicity and bubble size on coalescence behavior at a flat air-liquid interface and within a bubble column.

Model for Investigating Relationships between Surfactant Micropollutant Properties and Their Separation from Liquid in a Bubble Column.

The removal of surfactant micropollutants, such as dyes, pharmaceuticals, and proteins, through foam is very important in biotechnology and wastewater treatment. The literature shows that previous models consider mass balances within the foam but not the adsorption dynamics of micropollutant surfactants on bubble surfaces in the liquid solution. Thus, the main objective of this work is to examine the removal of surfactant micropollutants in a bubble column considering both mass balance and adsorption dynamics to calculate surfactant transport from the liquid bulk to the bubble surface.

Structures similar to lipid emulsions and liposomes. Dipalmitoylphosphatidylcholine, cholesterol, Tween 20-Span 20 or Tween 80-Span 80 in aqueous media.

In the present work, we show that we obtained nanometric structures made of water, 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), cholesterol (Chol), and a mixture of ethoxylated and non-ethoxylated sorbitan fatty acid esters (Tween 20, Span 20, Tween 80, and Span 80) by mixing all of them near the cloud point temperature (cp) of the ethoxylated surfactant. The influence that the constituents had on the size of the particle was determined by a pseudo-ternary phase diagram of water/Tween-Span/DPPC-Chol; the colloidal particles obtained were studied by differential scanning calorimetry, confocal fluorescence microscopy, scanning electron microscopy, and atomic force microscopy. These studies were made for all the systems with at least 23 d of colloidal stability.

STAND: Surface Tension for Aggregation Number Determination.

Taking advantage of the extremely high dependence of surface tension on the concentration of amphiphilic molecules in aqueous solution, a new model based on the double equilibrium between free and aggregated molecules in the liquid phase and between free molecules in the liquid phase and those adsorbed at the air/liquid interface is presented and validated using literature data and fluorescence measurements. A key point of the model is the use of both the Langmuir isotherm and the Gibbs adsorption equation in terms of free molecules instead of the nominal concentration of the solute. The application of the model should be limited to non ionic compounds since it does not consider the presence of counterions.

Phase Segregation at the Liquid-Air Interface Prior to Liquid-Liquid Equilibrium.

Binary systems with partial miscibility segregate into two liquid phases when their overall composition lies within the interval defined by the saturation points; out of this interval, there is one single phase, either solvent-rich or solute-rich. In most systems, in the one-phase regions, surface tension decreases with increasing solute concentration due to solute adsorption at the liquid-air interface. Therefore, the solute concentration at the surface is higher than in the bulk, leading to the hypothesis that phase segregation starts at the liquid-air interface with the formation of two surface phases, before the liquid-liquid equilibrium.

Gibbs excess and the calculation of the absolute surface composition of liquid binary mixtures.

Adsorption at the liquid-vapor interphase of a liquid binary mixture is traditionally quantified by means of the Gibbs solute excess. Despite several theoretical reviews on the meaning of Gibbs excess defined by the Gibbs dividing surface, it is still misinterpreted as the excess concentration under Guggenheim's finite-depth surface layer approach. In this work, both concepts are clarified in a practical way, aided by a graphical representation without loss of generality.

Analysis of Gibbs adsorption equation and thermodynamic relation between Gibbs standard energies of adsorption and micellization through a surface equation of state.

The calculation of surface molecular areas through Gibbs adsorption equation has been questioned in some early works on the belief that these areas have been obtained from the apparently constant slope of the surface tension vs. logarithm of concentration curve along the entire region at which surface tension declines rapidly as the concentration increases. This premise leads to consider that Gibbs equation predicts that surface saturation is reached at the beginning of this region.