Dynamical and structural properties of monohydroxy alcohols exhibiting a Debye process

We perform molecular dynamics simulations to study dynamical and structural properties of various primary monohydroxy alcohols. Comparing rotational correlation functions for the individual dipole moment of the molecules and the total dipole moment of the system, it is shown that the studied models exhibit a Debye process, which is slower than the a process, in harmony with experimental results. Performing cluster analysis, it is found that hydroxyl groups tend to form hydrogen-bonded aggregates, in particular, chain structures, which are transient in nature. To ascertain a possible relation between the Debye process and aggregate fluctuations, we devise an algorithm allowing us to follow the time evolution of transient chains. It is observed that the life times of transient chains are substantially shorter than the correlation times of the Debye process, indicating that the latter relaxation is not a direct consequence of the chain reorganization in the studied models. We assure that this conclusion is not affected when hydrogen-bond cooperativity is mimicked in the simulations or when the polarity of the molecules and the size of the systems are varied. On the other hand, we find that orientational correlations of molecular dipole moments are not limited to hydrogen-bonded chains, but they also exist in more globular regions around these objects, implying that the neighboring molecules are polarized in the dipole field exerted by the hydrogen-bonded chains. Further evidence for a relevance of dipole fields comes from the observation that some correlation between the initial orientation of the total dipole moment and the instantaneous orientations of the molecular dipole moments is retained up to the time scale of the Debye process. The simulation results are discussed in terms of a La-Ola wave model with diffusive propagation. (C) 2014 AIP Publishing LLC.