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Diffusivity in a non-ionic surfactant/water mixture of critical composition (1995)

Lesemann, M. ; Zielesny, A. ; Belkoura, L. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 102 (1995), S. 414-418

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Results of measurements of the temperature dependence of the mutual diffusion coefficient D of a tetraethyleneglycoloctylether (abbreviated C8E4) /water mixture of critical composition are reported (lower critical point, visually determined critical temperature Tc(vis)=40.587 °C; critical composition, mass fraction yc(C8E4)=0.071). The critical micelle concentration of C8E4 is smaller than the critical concentration, so that micelles are expected to be present in the mixture of critical composition. The reduced diffusion coefficients D*(=6πηξ/(kBT)⋅D) calculated from static and dynamic light scattering and viscosity data scale when plotted as function of the scaling variable x (=qξ) (η, shear viscosity; ξ, correlation length; D, diffusion coefficient; q, absolute value of scattering vector; kB, Boltzmann constant; T, temperature). They can be represented by the approximant of the dynamic scaling function proposed by Burstyn et al. [Phys. Rev. A 28, 1567 (1983)] assuming that the measured diffusion coefficient can be identified with the singular contribution (i.e., D=Dc). The influence of micelles on the critical properties of the system does not show up in the D* versus x plot. © 1995 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.469417

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Viscosity and diffusivity of a binary liquid mixture of critical composition: Study of the system 2-butoxyethanol/water (1994)

Zielesny, A. ; Schmitz, J. ; Limberg, S. ; [et al.]

Springer

International journal of thermophysics 15 (1994), S. 67-94

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ISSN: 1572-9567

Keywords: critical phenomena ; shear viscosity ; diffusivity ; dynamic scaling

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract Results of measurements of the temperature dependence of the shear viscosity and the mutual diffusion coefficient of a 2-butoxyethanol/water mixture of critical composition are reported. The shear viscosities are measured with a capillary viscometer, and the diffusion coefficients by dynamic light scattering. The viscosity data are used to determine the regular (background) and the singular (critical) part of the viscosity $$[\eta _b ;\eta = \eta _b (Q_0 \xi )^{z_\eta } ]$$ and to analyze the crossover regime.Q 0 has a value ofQ o = (1.54 ± 0.60) × 106 cm−1, which is small for a binary mixture of components of small molar mass. The viscosity is dominated by singular contributions in a narrow temperature range (T c − T) ≤ 1.2 K. The singular contributions can be neglected for temperatures (Tc−T) ≥ 11 K. The function η=ηb expz η H, given in the literature, represents the viscosity data in the temperature range 3 mK ≤ (T c − T) ≤ 25 K using the asymptotic form of the functionH for (q d/q c) → 0 (q d,q c, parameter of the theory). This limit corresponds to the case in which the background diffusion coefficient Lib can be neglected. The reduced diffusion coefficient D* calculated from the light-scattering data as a function of the scaling variable x(=qζ) is represented by the approximation of the dynamic scaling function proposed in the literature.