Structure and Dynamics of Hydrogen Bonded Liquids – StruDynaL

Hydrogen bonded liquids, such as water and alcohols, are literally vital components of all biological systems, and essential in pharmaceuticals, food products, cryo-protection agents, microwave chemistry, and many technologically relevant materials. Many important features are linked to their strong polarity that stems from the -OH dipole. Therefore, understanding the function of hydrogen bonded liquids requires knowledge of the structure and dynamics of both the molecules and the dipoles. It has been established for mono-alcohols, similar associated liquids, and possibly water, that the dipoles do not share the relaxation behavior or structure of the molecules: the prominent dielectric signal is a pure Debye type peak and slower than the relaxation of the remaining structure. This implies that the rationales for basic features of these hydrogen bonding liquids remain elusive to date.
Our approach to understanding the behavior of these liquids is based on merging the expertise of the US and French groups on dielectric relaxation, solvation dynamics, and calorimetric experiments, fabrication of nano-scale confinement, measurements in nano-porous structures, neutron and x-ray scattering, and MD computer simulations. The synergy of these techniques will allow us to probe the structure and dynamics of the -OH and -OR moieties on a wide range of length and time scales. Our hypothesis is that hydrogen-bonded clusters frustrate the -OH dynamics, while the calorimetric and mechanical behavior remains governed by the -OR mobility. Occurrence and size of preferred structures are assessed by sample confinement to spatial scales as small as 2 nm, while monitoring calorimetric and dielectric relaxation behavior. Variation of pore size and alkyl chain length will establish the volume required to sustain the relevant structures. The results will be correlated with pre-peaks observed in structure factor data of X-ray and neutron scattering and with effects of cluster separation by diluting with isoviscous alkanes. Significant support will come from MD simulations where structures and dynamics as well as shear stress and dipole moment correlators will be analyzed. Complimentary to the macroscopic dielectric and calorimetric techniques, dipolar, mechanical, and electron solvation dynamics experiments are targeted at probing the dynamics on a microscopic level. The goal is to provide a microscopic rationale for the origin of the slow Debye type polarization fluctuation and the role of hydrogen bonds regarding structure and dynamics in associated liquids.

An understanding of the structure/dynamics relation in hydrogen bonding liquids will clarify the great time scale separation of dielectric from mechanical and calorimetric modes, and thus capture the role of the hydrogen bond and its impact of the function and properties of these important liquids. This will include the interaction of such materials with electrical fields, e.g. the chemistry of hydrogen bonded solvents while heated by microwaves, and assessing damage to tissue originating from microwave exposure. Results will be broadly disseminated by publications, reviews, and conference presentations.