engleski

Clustering versus fluctuations in monohydroxy alcohols

It is well known that monohydroxy alcohols, such as methanol or octanol, tend to form chain-like clusters, principally due to the charge ordering induced by the OH hydroxyl groups, the oxygen being negatively charged, and the hydrogen positively charged. This local order can be detected by radiation scattering. What is less known is how the alkyl tails influence this local ordering. This topic can be studied by increasing the alkyl tails of the monohydroxy alcohols, from methanol all the way to undecanol, and the variation of the pre-peak monitored through computer simulations. By calculating the various atom-atom correlations and rebuilding the X-ray scattering spectra, we demonstrate that the flexibility of the alkyl tails with increasing sizes play a predominant role in determining the variation of the scattering pre-peak. The influence of branching in the alkyl tail is equally studied for the case of octanol. It is shown that the flexibility produces a transition in the pattern of chain ordering, which is related to the fluctuation of the methyl/methylene “field” surrounding the chained hydroxyl groups, and which occurs around 1-pentanol. This is an illustration of the hardness/softness change of meta-particles which are formed by the clustered entities within pure monomeric liquids.

alcohols ; scattering-experiments ; pre-peak ; computer-simulations

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