Comment on “Self-diffusion near the liquid–vapor critical point” [J. Chem. Phys. 114, 4912 (2001)]

Abstract

Drozdov and Tucker [J. Chem. Phys. 114, 4912 (2001)] have computed the self-diffusion coefficient along a near-critical isotherm showing anomalous slowing of molecular motion near the critical density and cite some experiments in support. A considered examination of the best literature data shows no such anomaly near neat liquid critical or mixture consolute points.

Critical Dynamics in a Binary Fluid: Simulations and Finite-Size Scaling

“…No anomalous critical behavior is detected and the linear behavior is consistent with previous simulation studies [6,15]. An MD calculation [16] has suggested a weak singularity in the self-diffusion near vapor-liquid criticality but no corresponding anomaly has yet been detected experimentally [17].…”

Dynamics of fluids near the consolute critical point: A molecular-dynamics study of the Widom–Rowlinson mixture

“…The key idea in finite-size scaling 78 is that the correlation length, , scales as the finite system's linear dimension, l, when grows beyond l, i.e., ϳ l when Ͼ Ͼ l. Ratios of the critical exponents can be obtained by computing the specific quantity at the critical point as a function of l. For example, at the critical point, ϳ ⑀ −␥ and ϳ ⑀ − , where ⑀ ϵ͉͑ − c ͒ / c ͉. 67,68 The shear viscosity and thermal conductivity increase as the density is increased and there is a critical enhancement. The ratio ␥ / can therefore be determined from the slope of a logarithmic plot of versus l. The static behavior of the model is consistent with what is expected from the Ising universality class.…”

A mode-coupling theory of diffusion in supercritical fluids

“…2 the MCT results for *ϭ s 2 /ͱm s ⑀ s together with the MD data of Heyes 79 ͓the MD values at T*ϭ1.41 were obtained by interpolating between the published values of * at T*ϭ1. 35 and T* ϭ1.456; the collision integrals ⍀ (2,2) *(T) required to compute E have been tabulated for the LJ potential 74 ͔. The Enskog contribution to the solvent shear viscosity coefficient, E * , is plotted separately in the middle panel of Fig.…”

“…As such, molecular diffusion coefficients in supercritical media have been actively studied via experiment, [9][10][11][12][13][14][15][16][17][18][19][20][21] molecular dynamics ͑MD͒ simulation, [22][23][24][25][26][27][28][29][30][31] and statistical mechanical theory. 26 -28,32-34 Due to the difficulties associated with measurements of diffusion coefficients at supercritical conditions, some of the experimental findings remain controversial, 33,35,36 which underscores the need for advancing theoretical treatments of SCF transport properties.…”