Understanding structure and dynamic behaviour of surfactants

What is it about?

Studies of molecules with polar 'head' groups and hydrophobic 'tails' with hydrocarbon chains of different length have been made over a wide range of temperatures. The structures have been determined and phases with rotational motion of the tails identified. For the surfactants that have been studied, the coordination of the ionic groups with the counter-ions causes packing with the tails strongly interdigitated. Calorimetry confirms the similarities and differences in phase behaviour in this series of surfactants.

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Photo by The Honest Company on Unsplash

Photo by The Honest Company on Unsplash

Why is it important?

The understanding that interdigitated layers of molecules are stabilised by ionic co-ordination provides an explanation for the thin bilayers that have been observed for alkyltrimethylammonium bromide surfactants adsorbed at various interfaces. The structures and phase changes are broadly similar for molecules with alkyl chain lengths from 10 to 18 but some transition temperatures vary. The different onset of rotational motion may explain some observed differences in bactericidal behaviour. The detailed information about structure and molecular volume as a function of temperature will be useful in modelling behaviour of various surfactants.