MOLECULAR-DYNAMICS STUDY OF THE THERMODYNAMIC AND STRUCTURAL-PROPERTIES OF METHANOL AND POLARIZABLE NON-POLARIZABLE CARBON-TETRACHLORIDE MIXTURES

Molecular dynamics simulations have been performed for methanol/carbon tetrachloride mixtures over the whole composition range at 323 K and zero pressure, The OPLS (optimized potentials for liquid simulation) p otential energy parameters by Jorgensen were used to model the methano l potential. Both a non-polarizable carbon tetrachloride model taken f rom McDonald, Bounds, and Klein [Mel. Phys, 45, 521 (1982)] as well as a polarizable model were used. The latter model was devised by combin ing the model of McDonald, Bounds, and Klein with the atomic polarizab ilities proposed by Applequist, Carl, and Fung [J. Am. Chem. Sec. 94, 2952 (1972)], We show that the role of the methanol-carbon tetrachlori de interactions are very important in discussing the thermodynamic mix ing properties, In order to reproduce the asymmetric behavior of the e xcess enthalpies with respect to composition it is necessary to includ e the non-additive polarization interaction. The structure and especia lly hydrogen bonding properties are discussed, Radial distribution fun ctions show a strong tendency of methanol to preserve the local order similar to the one in the pure fluid. The deviations from random mixin g are more pronounced at the lower mole fractions. This is explained b y a frustration model. At low methanol concentrations the molecules ge t more freedom to align themselves in energetically favorable (hydroge n bonded) configurations. Throughout the composition range, the majori ty of the methanol molecules,is found to be engaged in two hydrogen bo nd, As in the pure fluid, this leads tc, the pattern of hydrogen bende d winding chains. Upon dilution the degree of cross-linking between th e chains diminishes whereas the free monomer fraction rises. Furthermo re a significant number of the remaining chains close to form. cyclic polymers. (C) 1996 American Institute of Physics.