Low-frequency Raman studies of various concentrations of aqueous n-propanol at room temperature indicate that both water and n-propanol form single-component aggregates in solution. Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) studies also provide evidence of this tendency toward aggregation. Molecular dynamics simulations of 16% aqueous n-propanol, a concentration for which maximum segregation of n-propanol and water is observed, have been carried out in an attempt to elucidate the structure of these aggregates. Kirkwood-Buff integrals calculated from the radial distribution functions of the components show excellent agreement with experimentally derived values. Analysis of the atomic coordinates from the simulations reveal that approximately 50% of the n-propanol molecules are members of homogeneous hydrogen-bonded chains of up to 16 members in length, the majority of which are dimers. The g(r) data also indicate that a strong hydrophobic association exists between the hydrocarbon tails. This hydrophobic association is independent of hydrogen-bonding state, and results in the formation of an approximately 10-member micelle structure centered around the n-propanol chains. Water is excluded from the regions occupied by the n-propanol micelles. The water structure is largely unaffected except for a small amount of disruption at the interface between the bulk solvent and the n-propanol clusters, and the formation of small water clusters at the interface with the bulklike solvent that interact with hydroxyl groups at the ends of the propanol chains.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry