The phase transitions that occur in these systems involve The phase transitions observed in the surface pressure -moa liquid expanded-to-liquid condensed (LE/LC) state. Some lecular area ( p -A ) isotherms of monolayers of the dicarboxylic theories and mathematical models developed to describe compound octadecylmalonic acid ( OMA ) at the air / water interthese monolayer systems yield a first-order phase transition face were investigated using molecular dynamics simulation in (9)(10)(11)(12). Experimental evidence for a zero slope associated the molecular area ranging from 20 to 50 A 2 /molecule in a with this first-order transition has been obtained recently for triangular lattice. Potential energy, torsion angles, and hydralipid and fatty acid monolayers (13).
tion of the head groups under periodic boundary conditions
In this regard, the investigation of structural changes of a have been used for the study. Hydration was done by a stacked dicarboxylic lipid molecule in a Langmuir monolayer at the array of water molecules relaxing under these boundary conditions. Twelve simulations were performed at T ร
300 K to study air/water interface is of great interest. Normally these dicarthe conformation of the packed molecular system. Bonded and boxylic molecules when spread at the air/water interface may nonbonded interaction potentials were taken from Biosym force form a monolayer with two polar interfaces after compresfields. The transitions seen in the p -A curves are explained sion. Such monolayers find applications as spacers in electron from the breaks in the plots of potential energy at various contransfer experiments in complex multilayer systems (14, 15) centrations, related to a liquid expanded-to-liquid condensed or for the incorporation of a reactive group in or at the end ( LE / LC ) transition, and classified under the first order type. of a hydrocarbon chain for chemical reactions (16). In this Electron diffraction patterns of these films transferred onto study, a model dicarboxylic molecule octadecylmalonic acid transmission electron microscopy ( TEM ) grids were studied by (OMA, (CH 3 (CH 2 ) 17 CH(COOH) 2 ) was selected for the high-resolution imaging and showed a clear transition from the study of surface behaviour of the dicarboxylic amphiphiles. LE to the LC phase.