2014 Monolayers of synthetic lecithins as well as phosphatidic acid at different stages of ionization were studied with the film balance technique at pressures above the lateral vapour pressure. Pressure (03C0) versus area (a) curves (isotherms) and, by application of a special technique, area (a) versus temperature (T) curves (isobars) were recorded. From these data, plots of the lateral compressibility, ~, as a function of lateral lipid density (a-1) and of the thermal expansion coefficient, 03B1, as a function of temperature (T) were obtained. The well known transition (at T = TM) between the expanded (fluid) and the condensed (crystalline) states of the films, called the main transition, is characterized by a non-horizontal deflection of the isotherms (and isobars) in the coexistence region. A pronounced hysteresis shows that it is a first order transition. Two additional phase transitions, one at T > TM (fluid region) and one at T TM (crystalline region), were revealed by breaks in the slopes of the isotherms and the isobars. Discontinuities in the compressibilities and in the expansion coefficients show that these transitions are of second order. A flow experiment showed : that the fluid ~ fluid transition is also characterized by a pronounced discontinuity in viscosity. In fatty acid monolayers the transition (at T TM) between two crystalline states is of weak first order ( 2014 10 J./Mole). LE JOURNAL DE PHYSIQUE TOME 39, MARS 1978,

Polymorphism of phospholipid monolayers

Using ultrahigh vacuum scanning tunneling microscopy, we have characterized the structural phases of decanethiol on Au(111) at coverages below saturation. As coverage increases, the monolayer seque...

Coverage-Dependent Phases and Phase Stability of Decanethiol on Au(111)

Layer silicates and some other layer compounds can take up organic compounds such as long-chain alkanols and alkylammonium ions with formation of ordered bimolecular films This system enables new ideas to be developed concerning the structure of monomolecular and bimolecular films: the films form reversible kink-block and gauche-block structures Conclusions can be derived about the structure of the lipid layers in membranes

Kink‐Block and Gauche‐Block Structures of Bimolecular Films

The collapse of surfactant monolayers at the air—water interface

The Langmuir-Blodgett technique is a way of making ultrathin organic films with a controlled layer structure, which have many possible applications in technology for signal processing and transformation. Recent research has shown that their characteristics are strongly influenced by the highly anisotropic, essentially two-dimensional organisation of their constituent molecules. Novel effects in charge transport at the molecular scale ( approximately 1 nm) appear to be connected with very strong electron-phonon interactions, but are still not understood.

https://iopscience.iop.org/article/10.1088/0022-3727/23/4/001/pdf

Langmuir-Blodgett films

The gaseous, liquid, mesomorphous and solid states in monolayers are defined and their close connection with the corresponding states in three dimensions rigorously established. This involves a new treatment of the two‐dimensional liquid and of its transformation to the mesomorphous state. The properties of the three‐dimensional vitreous state of fatty substances are shown to be particularly important in connection with the behavior of monolayers. The different critical and transformation temperatures are also defined and their significance explained. From this is derived a systematic classification of the different types of isotherms observed. By determining the variations of the compressibility, viscosity and apparent dipole moment with change of area, higher order transformations are detected in monolayers. These transformations occur at the same areas as those at which ordinary phase transformations occur at lower temperatures.

D. G. Dervichian

Papers

Changes of Phase and Transformations of Higher Order in Monolayers