Forces between oil drops in polymer-surfactant systems: Linking direct force measurements to microfluidic observations

Abstract

Both microfluidics and atomic force microscopy have been used to quantify the forces between oil drops in the presence of complexes formed with anionic surfactant, sodium dodecyl sulphate, and neutral, water soluble polymer, poly(vinylpyrrolidone). Measurement and modelling of the interaction forces between both rigid and deformable surfaces demonstrated that the attraction between the drops is due to depletion forces, whereas the repulsive force is a combination of electrical double layer and steric forces, indicating complexes exist both in the bulk and at the drop interface. We developed a new microfluidic device to first form and then break-up chains of drops, where the drop break-up is sensitive to the underlying surface forces between the drops, not hydrodynamic drainage forces. The interaction behaviour between the force measurements and the microfluidic observations showed a strong correlation, where the observed adhesion between drops in the microfluidics is sensitive to the drop deformation and Laplace pressure. Correlation between the two techniques provides insight into the surface forces between drops in flowing systems. This work opens the possibility of developing high-throughput measurements of adhesive interactions between drops and has the potential utility in the formulation of emulsions.

Influences of Polymer–Surfactant Interaction on the Drop Formation Process: An Experimental Study

“…Therefore, it could be stated that by adding surfactants to the solution, they are attracted by hydrophobic parts of polymer chains, whereas electrostatic forces resist polymer–surfactant interaction. As the surfactant concentration exceeds the critical association concentration (CAC), hydrophobic effects are strong enough to overweigh repulsive forces, and SDS particles interact with the hydrophobic parts of CMC molecules and adsorb on them, which results in the expansion of molecular networks . Since these networks are rodlike structures, they interconnect with nearby molecular aggregates, − which results in the enhancement of solution viscosity. − With a further increase in the surfactant concentration below cmc, micelle structures form on the CMC molecules’ backbone.…”

Experimental Investigation on Microscopic Force Measurement of Foam and Heavy Oil

“…From the obtained curve, we found that the force decrease in the second half of the stretch was sharpened and the fluid displacement range changed less. In addition, combined with reference documents, − it is found that compared to liquid fluids, foams have more diverse interactions with crude oil because of the characteristics of a gas–liquid two-phase mixed system. The form of force between the two is also more complicated, except that the analysis of the factors mentioned in this article, as well as the influence of many factors such as fluid wettability, particle size, additive concentration, etc., needs to be studied, which has a large research space.…”

“…However, some researchers have conducted research on the interfacial forces of other microfluids. Dagastine et al − discussed the interaction between SiO 2 particles and oil-phase droplets in the water-phase environment and used microfluidic technology with microscopic measurement experiments to study the microforce between the oil droplets under the environmental conditions of the surfactant–polymer hybrid system and the pseudostatic aqueous system. They described the attraction between oil droplets in the poly­(vinylpyrrolidone) (PVP)/SDS system from multiple angles, summarized the action mechanism of the phase environment, fluid wettability, and other factors, and provided valuable experience for the study of the microscopic force between foam and heavy oil.…”

An overview of nanoemulsion characterization via atomic force microscopy

“…This approach allowed us to directly visualize and determine the position and absolute separation of the contacting oil droplets within 50 nm and also to quantify the deformation in the interfacial region during the interactions. In addition, through arbitrary estimation of the absolute separation between two oil droplet surfaces, based on theoretical models, the quantitative interpretation of the dynamic forces between micrometer-sized deformable oil droplets was reported (Aveyard et al 1996;Dagastine et al 2004;Gunning et al 2004;Dagastine et al 2006;Gromer et al 2010;Tabor et al 2011;Jamieson et al 2019).…”