Isomeric effects in structure formation and dielectric dynamics of different octanols

International audience; The understanding of the microstructure of associated liquids promoted by hydrogen-bonding andconstrained by steric hindrance is highly relevant in chemistry physics, biology and for many aspects ofdaily life. In this study we use a combination of X-ray diffraction, dielectric spectroscopy and moleculardynamics simulations to reveal temperature induced changes in the microstructure of different octanolisomers, i.e., linear 1-octanol and branched 2-, 3- and 4-octanol. In all octanols, the hydroxyl groupsform the bases of chain-, cyclic- or loop-like bonded structures that are separated by outwardlydirected alkyl chains. This clustering is analyzed through the scattering pre-peaks observed from X-rayscattering and simulations. The charge ordering which pilots OH aggregation can be linked to thestrength of the Debye process observed in dielectric spectroscopy. Interestingly, all methods used hereconverge to the same interpretation: as one moves from 1-octanol to the branched octanols, thecluster structure evolves from loose large aggregates to a larger number of smaller, tighter aggregates.All alcohols exhibit a peculiar temperature dependence of both the pre-peak and Debye process, whichcan be understood as a change in microstructure promoted by chain association with increased chainlength possibly assisted by ring-opening effects. All these results tend to support the intuitive picture ofthe entropic constraint provided by branching through the alkyl tails and highlight its capital entropicrole in supramolecular assembly.