Hysteresis of Mixed Monolayers of 2-[(Octadecylimino)methyl] phenol and Octadecylamine

Surface pressure-area isotherms and hysteresis of Langmuir films of 2-[(Octadecylimino) methyl]phenol (ODIMP) alone and mixed with octadecylamine (ODA) are described. Mixed surface films of ODIMP and ODA behave differently depending on whether the components are spread on the surface individually or what is spread instead is a previously mixed bulk solution. Hysteresis curves for pure ODIMP and both types of mixed films show that irreversible changes take place during the first compression, as isotherms obtained during the subsequent cycles have entirely different characteristics. A pure ODIMP monolayer irreversibly forms a bilayer during the first compression. Separately spread mixed films retain characteristics of the individual components, indicating non-homogeneity in the monolayer. Calculated areas per molecule of the film are consistent with the ODIMP part of the film collapsing and forming a bilayer as in its pure film. On the other hand, when a premixed solution is spread, there is no indication of a bilayer being formed. Instead, ODIMP is squeezed out of the film as it is being compressed.