Modeling of supramolecular structure and dielectric properties of butanols from melting point to supercritical state.

The supramolecular structure and dielectric properties of pure fluid butanols have been modeled in the temperature range from the melting point to the vicinity of the critical point using the quasichemical model of nonideal associated solution (QCNAS). The model of supramolecular structure takes into account both chain-like and cyclic aggregates. Dielectric permittivity and dipole correlation factor of n-, sec-, and tert-butanol are calculated in the temperature intervals 191-553, 166-533, and 298-503 K, respectively, using parameters obtained earlier for ambient conditions. The thermodynamic and structural parameters of supramolecular aggregation are reported. Size and structure distribution functions of aggregates are evaluated in the entire temperature range. Mean degree of aggregation of n-butanol decreases from hundreds at low temperatures to about 1.3 around critical point. The structure of n-butanol and s-butanol is characterized mainly by chain-like aggregation. tert-Butanol's degree of aggregation is about 4 at ambient conditions and falls to 1.4 approaching the critical point. The fractions of molecules in chain-like and cyclic aggregates are comparable for tert-butanol. This conclusion refutes the frequently expressed opinion that tert-butanol consists mostly of cyclic species.