Temperature dependence of interfacial tension of 2‐butoxyethanol/water mixtures near the lower critical point

Abstract

AbstractThe pendant drop method and the capillary rise method are used to measure the interfacial tension σ of 2‐butoxyethanol (2‐C4E1)/water mixtures near the lower critical point (critical composition, mass fraction of 2‐C4E1, yc = 0.2945; critical temperature Tc(visual) = 49.41°C) as function of temperature (0.6 K ≤ (T  Tc) ≤ 18.0 K). It is found that at temperatures 0.6 K ≤ (T  Tc) ≤ 7.0 K the temperature dependence of σ is represented by a power law of the form σ = σ0ϵμ (≤ = (T  Tc(visual))/Tc) with μ = (1.26 ± 0.02) and σ0 = (8.8 ± 0.2) mN m−1. The value of μ is consistent with the theoretically expected universal value of μ = 1.26. The amplitude ratio Rσ,ζ+ = σ0(ξ0ζ+)2/kBTc calculated from the system specific values of the critical amplitude σ0 and the critical amplitude ξ0 of the correlation length of local concentration fluctuations (ξ0ζ+ = (0.44 ± 0.04) nm) leads to a value of Rσ,ξ+ = (0.383 ± 0.070). It is close to the median value of Rσ,ξ+ calculated for several one‐ and two‐component fluids from experimental data taken from the literature (Moldover, Phys. Rev. A 31, 1022 (1985); median value Rσ,ξ+ = 0.386). – The ratio of [νT/R̄(∂T/∂z)] (νT, thermophoretic velocity (Marangoni convection); (∂T/∂z, temperature gradient) for droplets of radius R̄ of a 2‐C4E1) rich phase suspended in its coexisting H2O rich phase is calculated from the data.Values of [νT/R̄(∂T/∂z)] refering conditions along the liquid/liquid coexistence curve are given.