  The behavior at the air/water interface of multilamellar tubes made of the
ethanolamine salt of the 12-hydroxy stearic acid as a function of the
temperature has been investigated using Neutron Reflectivity. Those tubes are
known to exhibit a temperature tunable diameter in the bulk. We have observed
multilamellar tubes adsorbed at the air/water interface by specular neutron
reflectivity. Interestingly, at the interface, the adsorbed tubes exhibit the
same behavior than in the bulk upon heating. There is however a peculiar
behavior at around 50\degree for which the increase of the diameter of the
tubes at the interface yields an unfolding of those tubes into a multilamellar
layer. Upon further heating, the tubes re-fold and their diameter re-decrease
after what they melt as observed in the bulk. All structural transitions at the
interface are nevertheless shown to be quasi-completely reversible. This
provides to the system a high interest for its interfacial properties because
the structure at the air/water interface can be tuned easily by the
temperature.

Soft Condensed Matter