Dielectric and refractive index measurements for the systems 1-pentanol + 2,5,8,11,14-pentaoxapentadecane, or for 2,5,8,11,14-pentaoxapentadecane + octane at (293.15–303.15) K

Relative permittivities, ɛr, and refractive indices, nD, have been measured at (293.15–303.15) K, for the mixtures 1-pentanol + 2,5,8,11,14-pentaoxapentadecane (TEGDME) or TEGDME + octane. These data have been used, together with density measurements available in the literature, to calculate the correlation factors, gK, according to the Kirkwood–Fröhlich equations. The curves of the deviations of ɛr from the ideal behaviour, Δɛr, of the 1-pentanol + TEGDME system are shifted to high mole fractions of the alcohol, and show a rather large minimum. The shape of the Δɛr curves of methanol + TEGDME or +polyethylene glycol dimethyl ether 250 (PEG-250) mixtures is similar. This reveals that polyethers can break the alcohol self-association even at high alkanol concentrations. The higher Δɛr values of the methanol solutions are ascribed to large self-association of this alcohol. The Δɛr curves of the 1-pentanol + dibutyl ether (DBE) system are nearly symmetrical, and the Δɛr values are higher than those of the corresponding TEGDME mixture. This indicates that effects related to the alcohol self-association are much more relevant in the DBE system. These findings are supported by gK and molar polarization data. Values of molar refraction of 1-pentanol systems reveal that dispersion forces become more important in the sequence: octane < DBE < TEGDME. Such forces are also more relevant in the 1-pentanol + TEGDME system than in the methanol + TEGDME solution. The comparison of ɛr and gK data for TEGDME or DBE + octane mixtures shows than the polyether is a more structured liquid.

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► ɛr and nD have been measured at (293.15–303.15) K for 1-pentanol + TEGDME or TEGDME + n-C8.
► Correlation factors have been calculated according to the Kirkwood–Fröhlich equations.
► Polyethers can break alcohol self-association at high alkanol concentrations.
► Effects due to alcohol self-association are much relevant in systems with monoethers.
► Conclusions are supported by gK and molar polarization data.