In tune with your emulsions
Our ChemSci Pick of the Week describes a new method to predictably tune emulsions – which could lead to new methods of drug delivery, cosmetic manufacture, or power generation.
An emulsion is a blend of materials which do not normally mix, such as oil and water. Various types of emulsions have different textures, behaviour and properties, which make them useful for food, pharmaceutical, cosmetic and agricultural products.
For the first time, researchers have been able to controllably split water and oil emulsions through osmosis – the same process that moves water between cells in your body, or from soils into the roots of plants.
To explain their work, published in Chemical Science, scientists from Tsinghua University in China used the example of making a salad dressing: "When you make a dressing, the oil and vinegar never mix," said corresponding author Professor Guangtao Li. "However, imagine a drop of oil in vinegar which contains a lot of salt inside.
"The presence of the salt draws vinegar into the oil droplet. When the vinegar goes into the droplet, it forms a series of patterns depending on the amount of salt inside the oil. Then you can enjoy a unique and beautiful salad!"
The researchers’ breakthrough was possible by using inorganic salts to draw water into oil from surrounding ionic liquids by generating an osmotic pressure – just like in the salad dressing. They found that one mixture in particular – organic salt LiTf2N and ionic liquid 1-alkyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide – showed unique properties.
The separation process could be controlled with unprecedented flexibility and range, resulting in the one-step fabrication of diverse, complex emulsion structures.
This was possible due to the extent of the inorganic salt’s solubility in the ionic liquid, and also the easily-tailorable molecular structure of the ionic liquid. Fine-tuning and control of separation direction could then be achieved by adding further salt into the liquid. Interestingly, this process was reversible, by re-drawing water molecules taken up.
The method was the result of curiosity-driven research by the chemists, who had noticed the phenomenon during other experiments, and were keen to understand the background mechanism. They hope that it can lead to the separation of a wide range of substances.
"This work could be used to fabricate porous materials and complex emulsions which are widely used in the drug-delivery, cosmetic, agricultural industries, and so on," Professor Gao said. "In a longer-term period, our research could shed light on the purification of seawater and seawater power generation. This could help to resolve the increasing freshwater and energy shortage problems."
This article is free to read in our open access, flagship journal Chemical Science: Ning Gao, Jiecheng Cui et al., Chem. Sci., 2019, Advance Article. DOI: 10.1039/C9SC01649J. You can access our 2019 ChemSci Picks in this article collection.