First Observation of a Thermal Contraction-Type Phase Transition in A-T Isobars of Monolayers at the Air/Water Interface with Temperature Increase

A-T isobars of octadecylurea monolayers were measured. This is the first direct observation that the monolayers exhibited a first-order phase transition accompanying discontinuous molecular area contraction with increasing temperature. This may be due to the “fusion” of a hydrogen bonded bulky structure of urea head groups in the monolayers at the water surface.