Dynamic equivalence between atomic and colloidal liquids

¹ Facultad de Ciencias Fisico-Matemáticas, Benemérita Universidad Autónoma de Puebla Apartado Postal 1152, 72000 Puebla, Pue., México
² Instituto de Física “Manuel Sandoval Vallarta”, Universidad Autónoma de San Luis Potosí Álvaro Obregón 64, 78000 San Luis Potosí, SLP, México
³ Departamento de Física, Universidad de Sonora - Boulevard Luis Encinas y Rosales, 83000 Hermosillo, Son., México
⁴ Unidad Académica de Física, Universidad Autónoma de Zacatecas - Paseo la Bufa y Calzada Solidaridad, 98600 Zacatecas, Zac., México
⁵ Departamento de Física Aplicada CINVESTAV-IPN Unidad Mérida - Apartado Postal 73 Cordemex, 97310 Mérida, Yuc., México

Received: 18 May 2012
Accepted: 17 July 2012

Abstract

We show that the kinetic-theoretical self-diffusion coefficient of an atomic fluid plays the same role as the short-time self-diffusion coefficient D_S in a colloidal liquid, in the sense that the dynamic properties of the former, at times much longer than the mean free time, and properly scaled with D_S, will be indistinguishable from those of a colloidal liquid with the same interaction potential. One important consequence of such dynamic equivalence is that the ratio D_L/D_S of the long-time to the short-time self-diffusion coefficients must then be the same for both an atomic and a colloidal system characterized by the same inter-particle interactions. This naturally extends to atomic fluids a well-known dynamic criterion for freezing of colloidal liquids (Löwen H. et al., Phys. Rev. Lett., 70 (1993) 1557). We corroborate these predictions by comparing molecular and Brownian dynamics simulations on the hard-sphere system and on other soft-sphere model systems, representative of the “hard-sphere” dynamic universality class.