Chemists have used an electron microscope to explore the mystery behind the ‘ouzo’ effect, whereby water is added to a clear alcohol spirit, and the drink turns milky-white. The team behind this work hopes it will improve emulsions for paints, drugs, and plastics.

Scientists have known for many years that the ouzo effects – also seen in spirits like pastis or sambuca- are caused by three transparent components of the drink: water, anise extract, and ethanol, forming an emulsion that scatters light instead of mixing. The resulting emulsion, however, still needs to be fully understood. It’s also highly stable without the need for a surfactant. It’s a natural process of the assembly of molecules, says Nathan Gianneschi, professor of chemistry at Northwestern University in the US.

Gianneschi and his colleagues investigated the ouzo effects 1 using a liquid-phase transmission electron microscope 2. This device can image hermetically sealed slides containing liquid samples. The researchers found that droplets of hydrophobic oil and ethanol did not grow more significantly than a few nanometres but formed a more defined ‘bubble-like structure with a darker ring around the exterior and a paler inner surface.

Gianneschi explains that the droplets don’t continue to grow and become destabilized. Gianneschi explains that the droplets do not continue to grow or become destabilized. This is the first time an LPTEM was used to study the ouzo effects. It shows that the instrument can image liquids in a way that cannot be done otherwise. Gianneschi says that there has been a flurry in the last eight years of using the technique to photograph soft matter. It’s been a time when technology has enabled science.

He hopes that by better understanding the ouzo effects, he can create highly stable emulsions for other applications such as paints, adhesives, and plastics. He says that a better understanding of emulsions could be helpful in the oil industry and help reduce environmental damage from oil spills.

Pernod, a physical chemist at AgroParisTech, also studied the Ouzo effect. He claims that some previous studies had reached similar conclusions. He says, ‘I love the experimental setting and how they validated the results with this method.’

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