Scientists at MIT have developed a way to combine oil and water, creating a substance that can remain stable for long periods and does not require shaking. The new process may find applications in processed foods as well as pharmaceuticals, cosmetics and other sectors.

 

Less energy-intensive

 

For many uses, including new drug-delivery systems and food processing methods, it is important to be able to get oil in water (or water in oil) to form tiny droplets – only a few hundred nanometres across, too small to see with the naked eye – and to have them stay tiny rather than merging into larger droplets and eventually separating from the other liquid.

 

In industrial settings, such emulsions tend to be made by either mechanically shaking the mix or using sound waves to initiate intense vibrations within the liquid – a process known as sonicating. However, both of these processes are energy-intensive, requiring more energy to create finer drops, while the newly discovered method is very energy-inexpensive.

 

The new process involves cooling a bath of oil containing a small amount of a surfactant that can bind to both oil and water molecules, and then allowing water vapour from the surrounding air to condense onto the oil surface. Experiments have shown that this can produce tiny, uniform water droplets on the surface that then spread through the oil, and their size can be controlled by adjusting the proportion of surfactant used.

 

Nanoscale emulsions

 

The findings of MIT graduate student Ingrid Guha, associate professor Kripa Varanasi, and former postdoc Sushant Anand, who is now an assistant professor at the University of Illinois, are reported in the journal Nature Communications. In their experiments, the team produced nanoscale emulsions that remained stable over periods of several months, compared to the few minutes it takes for the same mixture of oil and water to separate without the added surfactant.

 

“Our bottom-up approach of creating nanoscale emulsions is highly scalable owing to the simplicity of the process,” Anand said. “We have uncovered many new phenomena during this work. We have found how the presence of surfactant can change the oil and water interactions under such conditions, promoting oil spreading on water droplets and stabilising them at the nanoscale.”

 

“It’s such an important thing,” added Varanasi, due to the fact that “foods and pharmaceuticals always have an expiration date” that often relates to the instability of the emulsions they contain. 

 

“We envision that you could use multiple liquids and make much more complex emulsions,” revealed Guha, stating that besides being used in food, cosmetics and drugs, the method could have other applications, such as in the oil & gas industry, where the drilling fluids sent down wells are also emulsions.

 

The work was supported by the MIT Energy Initiative, the National Science Foundation, and a Society in Science fellowship.