• Use Case

Published on October 31, 2022 by rheocube

Looking at specific products (e.g. cleaning products), surfactants help deliver key functions of the product and surfactants are there to help delivery. However, surfactants can be troublesome with stability, or interactions between surfactants. RheoCube can play a role in helping understand the stability of the chemical properties.

Alignment of surfactants at fluid interfaces plays an important role in stabilisation of emulsions. Emulsion stability is a hot topic in many industries, including food, cosmetics, paints and coatings. The chemical structure and geometry of the surfactant have a direct effect on the size of the droplets and the surfactants performance in stabilising the emulsion. In this use case, we investigate the effect of different surfactants on the stability and size of the droplets in an oil in water emulsion.

Finding the right surfactant to stabilise emulsions at a certain droplet size in a wet lab is often time-consuming and complicated. Trial-and-error is a common practice in industry, mainly due to the many factors influencing droplet size distribution and stability. One such factor is the role of the surfactant and how it behaves at the oil-water interface. Simulations at the molecular scale can help to better understand this behaviour. In RheoCube, molecular dynamics simulations are used to perform easily accessible molecular-scale virtual experiments. Through powerful 3D visualisations, the alignment of the surfactants at the oil/water interface can be studied.

Snapshots of the simulations of oil in water emulsions with Span 80, Tween 80, a combination of Span 80 and Tween 80 (1:1) and POE20 respectively.

In this industry use case, we investigate the effect of the commercially available Tween 80 and Span 80 surfactants, and a polyoxyethylene oleyl ether surfactant with a long hydrophilic chain (POE20) on the stability of an emulsion of isopropyl myristate (oil) in water. All virtual experiments were performed with (1:1) ratio of oil and water and a total concentration of 20% in volume of surfactants.

The results show that Tween 80 and Span 80 align well at the oil/water interface. POE20 forms a very rough interface which points to low performance in stabilising emulsions. As the coverage is not optimal, droplets have a higher tendency to merge. Furthermore, both Tween 80 and Span 80 systems exhibit a large curvature at the interface, while the combination of both does not introduce curvature. Large curvatures are indicative of a surfactant's ability to stabilise small droplets.

Optimization of emulsions in industry is mainly achieved by trial-and-error. One of the challenges is finding the right surfactant. RheoCube can help understand how surfactant structure influences emulsion stability by capturing the behaviour at the oil-water interface. These insights are hard to obtain experimentally and can help reduce wet-lab experimentation.