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Chemists at Sheffield University have demonstrated a 10–12-fold mechanical expansion in their porphyrin film material upon exposure to acid vapour.

Porphyrins are intensely coloured compounds — naturally found in the haem of blood cells and chlorophyll of plants — that have the ability to readily form complexes.

The team has been investigating the use of synthetically created porphyrin as thin layers floating on a water surface — referred to as Languier films.

‘When you expose them to an acid vapour you protonate the porphyrin rings, they go from a neutral state to [being] charged,’ project lead Dr Tim Richardson of Sheffield told The Engineer.

‘Imagine a load of two pennies stacked close together and suddenly they repel to become facedown and flat on the surface.’

Furthermore, this expansion can be reversed through deprotonation allowing contraction to recur, Richardson added.

The group has now verified the phenomenon in the lab using ammonia gas as the anylate to create a 10–12-fold mechanical expansion, validated with a reflectometer at the ISIS facility at the Rutherford Appleton Laboratory.