Unexpected Order-Disorder Transition in Diacetylene Alcohol Langmuir Films

The phase diagram of the Langmuir film of diacetylene alcohol-henicosa-5,7-diyn-1-ol-is investigated by means of surface pressure versus surface area isotherms, Brewster angle microscopy, X-ray reflectivity, and grazing incident Xray diffraction. Among the usual phases described in the generic phase diagram of small head group molecules, one observes an unexpected reversible transition from an ordered condensed phase to a disordered one upon increasing the surface pressure. We postulate that the origin of this unusual, unprecedented transition results from the competition between the interactions between the diacetylene blocks in the hydrophobic chain and the hydrogen bonds between head groups and water.

Automated summary

The phase diagram of a Langmuir film was studied, revealing an unexpected reversible transition from an ordered condensed phase to a disordered one, possibly due to the competition between interactions within the hydrophobic chain and hydrogen bonds between head groups and water.