Test of the Universal Scaling Law of Diffusion in Colloidal Monolayers

Abstract

Using the techniques of optical microscopy and particle tracking, we measure the pair correlation function and Brownian diffusion in monolayers of strongly interacting colloidal particles suspended at or near three different interfaces and test the universal scaling law of the normalized diffusion coefficient, D[over ˜]≃e(αΔS), as a function of the excess entropy ΔS for a wide range of particle concentrations. It is found that the universal scaling law with α=1 holds well for highly charged polystyrene spheres suspended at an air-water interface, where the strong electrostatic interactions play a dominant role. For monolayer suspensions of hard-sphere-like particles, where hydrodynamic interactions become important, deviations from the universal scaling law are observed. The experiment indicates that the hydrodynamic corrections could be incorporated into the universal scaling law of diffusion with an exponent α<1.

Pair potentials for warm dense matter and their application to x-ray Thomson scattering in aluminum and beryllium

“…From inelastic data for shock-compressed Al (hereafter Al-II), Ma et al [12] determined the experimental conditions in the target to be ρ/ρ 0 = 3.0 and T e = 10 eV. This density corresponds to r ws = 2.07 a.u.…”

“…Recent laser experiments on solid simple metals have reached WDM conditions through e.g., (i) ultrafast isochoric heating (ρ = ρ 0 , where ρ 0 ρ are the initial and final densities, respectively) [7][8][9], and (ii) shock-compression (ρ > ρ 0 ) [10][11][12][13][14]. In situation (i) the optical laser directly interacts with a metallic target and couples to the free electrons causing their temperature T e to reach many eV, while ions remain approximately at their initial temperature T i .…”

“…In particular, the need for a simple potential has led to the use of an intuitive model that has come into vogue with WDM studies, viz. the "Yukawa + short-ranged repulsive (YSRR) potential" [10,12,26],…”

“…The utility of the NPA-HNC and the possibility of two-temperature systems in laser-generated WDM is illustrated below by re-analyzing experiments on Al and Be. For Al, we examine shock-compressed systems by (i) Fletcher et al [10] at ρ/ρ 0 = 2.32 and T e = 1.75 eV and by (ii) Ma et al [12] at ρ/ρ 0 = 3.0 and T e = 10 eV with ρ 0 = 2.7 g/cm 3 ; for Be, we examine the shockcompressed system by (iii) Lee et al [13] at ρ/ρ 0 = 2.99 and T e = 13 eV and the isochorically-heated system by (iv) Glenzer et al [14] at ρ/ρ 0 = 1 and T e = 12 eV with ρ 0 = 1.85 g/cm 3 .…”

Anisotropic diffusion of concentrated hard-sphere colloids near a hard wall studied by evanescent wave dynamic light scattering

“…Moreover, flows of dilute or concentrated suspensions in confined environments are ubiquitous in industrial processes such as food processing and oil recovery. 7 Under such confined conditions, near surfaces, interfaces, and in microchannels, particle dynamics are affected both by direct enthalpic interactions 8 as well as excluded volume and hydrodynamic interactions (HI). 9 While the former are system specific and depend on the specific interaction energy between the moving particles/polymers and the surfaces/interfaces, HI are expected to depend generically on the a) Author to whom correspondence should be addressed.…”