Study of Mesoscale Structure and Dynamics of Associated Liquid 2-propanol by Neutron Scattering and Molecular Dynamics Simulations

Monohydroxy alcohols are good model systems for studying the impact of hydrogen bonding on the structure and dynamics of liquids and on the macroscopic transport properties such as viscosity. We investigated 2-propanol by static and quasielastic neutron scattering experiments on a series of partially and fully deuterated samples at temperatures ranging from the liquid, the deeply supercooled, to the glassy state. Corresponding Molecular Dynamics (MD) simulations are performed to further understanding the collective dynamics of the system. We focus on the mesoscale structures associated to the structure factor pre-peak at wavevector Q ~ 0.8 Å^-1. The dynamics of these molecular associates is at least one order of magnitude slower than the dynamics at the structure factor peak, at Q ~ 1.4 Å^-1. MD simulations show that 2-propanol molecules prefer to form chain-like structures with approximately 10% of the rings although the hydroxyl group is located in a non-terminal position. The emergence of multiple relaxation processes as the system is cooled towards the melting temperature and below is observed, which could be related to the non-Arrhenius increase of the viscosity.