Coexistence curve and turbidity of aqueous solutions of oligooxyethylene alkyl ether with the addition of urea near the critical point

Abstract

Coexistence curves and turbidity of aqueous solutions of tetraoxyethylene mono-n-octyl ether C8E4 without and with the addition of urea were examined focusing on the critical behavior. The critical exponent β, which characterizes the shape of coexistence curve, for aqueous C8E4 solution was determined as 0.329±0.003 in agreement with 3D Ising model. Turbidity measurement for aqueous C8E4 solution also yielded Ising values γ=1.26±0.05 and ν=0.63±0.02 for the critical exponents of the isothermal compressibility and correlation length, respectively. Addition of urea up to 7 M concentration did not modify the critical exponents, although the critical temperature increased by about 20 °C with the addition of urea. Coexistence curves of oxyethylene mono-isobutyl ether C4E1 with the addition of 7 M urea also yielded β=0.326±0.002 in agreement with 3D Ising model. These are in contrast to our recent results that the critical exponents for heptaoxyethylene mono-n-tetradecyl ether C14E7 in an aqueous salt solution were modified to Fisher’s renormalized Ising values by the addition of salt [J. Chem. Phys. 109, 711 (1998)]. The difference in the critical behavior for the nonionic surfactant solutions might be attributed to the solution structure, structure of micellar aggregation of surfactant.

Conjectures on the exact solution of three-dimensional (3D) simple orthorhombic Ising lattices

“…154,[283][284][285][286][287][288][289][290][291][292][293] Again, we emphasize here that the difference between the logarithmic behavior and the character of the non-zero critical exponent α in range of 0.077 -0.12 cannot be distinguished by experiments, specially, in case of preseting the existence of the non-zero critical exponent α. The putative exact critical exponent γ is in very good agreement with the experimental data, 154,[284][285][286]288,290,291,[294][295][296] specially, which is exactly the same as what was determined in various references. 283,287,292,293 Most of the experimental data for β, η and ν have somewhat larger deviations with the exact values, remaindering us the fact that only is the critical exponent γ the most reliable one for the high -accurate determination of the critical exponents since it depends most insensitively on the accurate location of the critical point.…”

Thermal Diffusion of Dextran in Aqueous Solutions in the Absence and the Presence of Urea

“…The sign inversion behavior of S T is diminished by the addition of urea. Although the role of urea for destroying the local water structure is still controversial, ,,, it indicates that the thermal diffusion behavior considerably depends on the modification of local structures of water; that is, a modification of short-range interactions has a dominant role for the sign inversion of Soret coefficient of aqueous solutions of dextran.…”

Near-critical dynamical behavior of an ionic micellar solution

“…Such an increase of the critical exponent has been ascertained for various ternary systems. [21][22][23][24][25][26][27] Moreover, it has been suggested that the critical exponents of the systems associated with the polydisperse polymer could be described by Fisher's renormalization. 28,29 II.…”