More to droplets than meets the eye. Salads, shampoos and mining to benefit from theoretical research into droplets

But the result could be the improvement of the design and production of everyday products worth hundreds of millions of dollars.

They have developed a technique to measure the tiny forces between droplets in liquids. For the first time, the researchers can measure the attraction between oil droplets in water—and this has application for products ranging from milk and ice-cream to shampoos, drugs, and even mineral processing.

All these instances involve emulsions, the dispersion of droplets of oil through water.

“This was a truly multi-disciplinary effort,” says team member Dr Raymond Dagastine from the Particulate Fluids Processing Centre in the Department of Chemical and Biomolecular Engineering at the University of Melbourne.

“We had chemists, chemical engineers and mathematicians all working together because, not only did we have to figure out how to hold and push two tiny droplets together, and how to measure their interaction, but we also needed to interpret the information we collected.”

Raymond is one of sixteen early-career scientists selected from across Australia for the national competition Fresh Science. One of the Fresh Scientists will win a study tour to the UK where they will have the opportunity to present their work at the Royal Institution.

An experimental tool known as an Atomic Force Microscope was used to drive two oil droplets together in water very carefully at different speeds. The researchers developed a theoretical analysis to describe the collisions. In the end they were able to measure, understand and even predict how emulsion droplets interact with each other.

Emulsions are made of droplets of one liquid colliding with each other in another liquid.

Some droplets collide and bounce away, while others can collide and stick together or coalesce. It may seem simple, but the physics behind controlling whether the oil and water remain dispersed or how fast they separate is a key variable in the purification steps in pharmaceutical and minerals processing.

In addition, the separation that happens in salad dressing can be prevented from happening in products such as shampoo, milk and even ice cream. “It all could lead to improvements such as shampoos that clean better and mineral processing equipment that is smaller and more efficient,” Raymond says.

This work was recently published in Science the weekly journal of the American Association for the Advancement of Science.