Indexed on: 11 Jun '11Published on: 11 Jun '11Published in: Journal of Physical Chemistry B
The unusual properties of poly(ethyleneoxide) + alcohol mixtures were analyzed using a poly(ethylene oxide) monomer (1,2-dimethoxyethane) in ethanol solutions as a model. A collection of thermophysical measurements and computational studies, using density functional theory and classical molecular dynamics approaches, provide valuable information about the molecular-level structure of this mixture and on the interaction between 1,2-dimethoxyethane and ethanol molecules. Thermophysical measurements show remarkable deviations from ideality, which are related to the development of intermolecular hydrogen bonding between both molecules upon mixing and to the balance of homo- and heteroassociations. Density functional theory allows better characterization from energetic and structural viewpoints. In this work, the characteristics for the different 1,2-dimethoxyethane/ethanol hydrogen-bonding complexes are analyzed via atoms in a molecule and natural bond orbital methods. Classical molecular dynamics simulations are carried out for pure 1,2-dimethoxyethane and for mixtures in the whole composition range. Force field validation is done by comparison of predicted thermophysical properties with measured ones and through the analysis of 1,2-dimethoxyethane conformers. Structural features are inferred from the analysis of radial and distribution functions and their evolution with composition, together with the study of molecular distribution in the mixed fluids (microheterogeneities). Dynamic aspects of the mixtures' behavior are inferred from the calculated self-diffusion constants and mean square displacements. The whole study points to a highly structured fluid, whose structure is determined by the balance of the 1,2-dimethoxyethane disrupting effect on the ethanol hydrogen-bonding network and the appearance of microheterogeneities.