TEMPERATURE-DEPENDENCE OF INTERFACIAL-TENSION OF 2-BUTOXYETHANOL WATER MIXTURES NEAR THE LOWER CRITICAL-POINT

The pendant drop method and the capillary rise method are used to measure the interfacial tension sigma of 2-butoxyethanol (2-C4E1)/water mixtures near the lower critical point (critical composition, mass fraction of 2-C4E1, y(c), = 0.2945; critical temperature T(c)(visual) = 49.41-degrees-C) as function of temperature (0.6 K less-than-or-equal-to (T - T(c)) less-than-or-equal-to 18.0 K). It is found that at temperatures 0.6 K less-than-or-equal-to (T - T(c)) less-than-or-equal-to 7.0 K the temperature dependence of sigma is represented by a power law of the form sigma = sigma0epsilon(mu) (epsilon = (T - T(c)(visual))/T(c)) with mu = (1.26 +/- 0.02) and sigma0 = (8.8 +/- 0.2) mN m-1. The value of mu is consistent with the theoretically expected universal value of mu = 1.26. The amplitude ratio R(sigma,xi)+ = sigma0(xi0+)2/k(B)T(c) calculated from the system specific values of the critical amplitude sigma0 and the critical amplitude xi0 of the correlation length of local concentration fluctuations (xi0+ = (0.44 +/- 0.04) nm) leads to a value of R(sigma,xi)+ = (0.383 +/- 0.070). It is close to the median value of R(sigma,xi)+ calculated for several one- and two-component fluids from experimental data taken from the literature (Moldover, Phys. Rev. A 31, 1022 (1985); median value R(sigma,xi)+ = 0.386). - The ratio of [upsilon(T)/RBAR(partial derivative T/partial derivative z)] (upsilon(T), thermophoretic velocity (Marangoni convection); (partial derivative T/partial derivative z, temperature gradient) for droplets of radius RBAR of a 2-C4E1 rich phase suspended in its coexisting H2O rich phase is calculated from the data. Values of [upsilon(T)/RBAR(partial derivative T/partial derivative z)] referring conditions along the liquid/liquid coexistence curve are given.