We employ the principle of dynamic equivalence between soft-sphere and hard-sphere fluids [Phys. Rev. E 68, 011405 (2003)] to describe the interplay of the effects of varying the density n, the temperature T, and the softness (characterized by a softness parameter ν(-1)) on the dynamics of glass-forming soft-sphere liquids in terms of simple scaling rules. The main prediction is the existence of a dynamic universality class associated with the hard-sphere fluid, constituted by the soft-sphere systems whose dynamic parameters depend on n, T, and ν only through the reduced density n*≡nσ(HS)(T*,ν). A number of scaling properties observed in recent experiments and simulations involving glass-forming fluids with repulsive short-range interactions are found to be a direct manifestation of this general dynamic equivalence principle.

A recently developed theory of collective diffusion in colloidal suspensions is tested regarding the quantitative accuracy of its description of the dynamics of monodisperse model colloidal systems without hydrodynamic interactions. The idea is to exhibit the isolated effects of the direct interactions, which constitute the main microscopic relaxation mechanism, in the absence of other effects, such as hydrodynamic interactions. Here we compare the numerical solution of the fully self-consistent theory with the results of Brownian dynamics simulation of the van Hove function G(r,t) and/or the intermediate scattering function F(k,t) of four simple model systems. Two of them are representative of short-ranged soft-core repulsive interactions [(sigma/r)(mu), with mu>>1], in two and in three dimensions. The other two involve long-ranged repulsive forces in two (dipolar, r(-3) potential) and in three (screened Coulomb, or repulsive Yukawa interactions) dimensions. We find that the theory, without any sort of adjustable parameters or rescaling prescriptions, provides an excellent approximate description of the collective dynamics of these model systems, particularly in the short- and intermediate-time regimes. We also compare our results with those of the single exponential approximation and with the competing mode-mode coupling theory.

We report the direct measurement by video microscopy of the Van Hove function of quasi-twodimensional colloidal suspensions. Under these conditions of confinement, the effective interparticle potential exhibits an intermediate range attractive component. This is obtained by deconvoluting the measured pair correlation function using an inverse Monte Carlo method. The experimental dynamic behavior is well represented by a Brownian dynamics simulation, performed using the experimental pair potential and an effective quasi-two-dimensional short-time diffusion coefficient.[S0031-9007 (98)06595-8] PACS numbers: 82.70.Dd, 05.40. + jThe study of colloidal suspensions under conditions of severe confinement is a topic of considerable current interest. This is due to the practical importance of such systems, and to the many fundamental questions that these systems present to the field of colloid physics. To illustrate the latter, let us mention the recent measurements of the effective pairwise forces between charged spherical particles of aqueous suspensions confined between two glass plates [1-3]. These measurements suggest that two charged particles under those conditions of confinement attract, rather than repel, each other at intermediate distances. So far, there is not a plausible explanation of such an attractive component of the measured effective pair potential, u ef ͑r͒. Because of the fundamental relevance of this observed feature, it is worthwhile to characterize in still more detail the properties of these effective forces, through the measurement of other properties that depend on them. This is what we do in this work by analyzing the Van Hove function of the system.For this, it is instructive to recall what was the situation with respect to the same system (an aqueous suspension of highly charged colloidal particles) in the absence of confinement, i.e., in the three-dimensional bulk. In this case, the direct measurement of the forces between two particles was performed rather recently [3,4]. However, the indirect determination of these forces had been made many years before. Thus, in a first step, the static structure factor of the suspension, measured by static light scattering, was employed to determine the effective pairwise forces by adjusting the experimental data using computer simulations and approximate liquid state theories [5][6][7]. Then, this experimentally extracted pair potential was employed to do Brownian dynamics simulations of the main dynamic properties of the suspension, and the predictions were compared with dynamic light scattering results [5][6][7]. The agreement was a further evidence of the accuracy of this indirect experimental determination of the effective pair potential, for which a theory was already available, namely, that developed by Derjaguin, Landau, Verwey, and Overbeek (DLVO) [8]. In contrast, in our present case, no theory analogous to the DLVO theory is available. However, the effective pair potential has been determined indirectly [1,2], by measuring the radial distribut...

In this work, we used a sequential method of synthesis for gold–silver bimetallic nanoparticles with core@shell structure (Au@AgNPs). Rumex hymenosepalus root extract (Rh), which presents high content in catechins and stilbenes, was used as reductor agent in nanoparticles synthesis. Size distribution obtained by Transmission Electron Microscopy (TEM) gives a mean diameter of 36 ± 11 nm for Au@AgNPs, 24 ± 4 nm for gold nanoparticles (AuNPs), and 13 ± 3 nm for silver nanoparticles (AgNPs). The geometrical shapes of NPs were principally quasi-spherical. The thickness of the silver shell over AuNPs is around 6 nm and covered by active biomolecules onto the surface. Nanoparticles characterization included high angle annular dark field images (HAADF) recorded with a scanning transmission electron microscope (STEM), Energy-Dispersive X-ray Spectroscopy (EDS), X-Ray Diffraction (XRD), UV–Vis Spectroscopy, Zeta Potential, and Dynamic Light Scattering (DLS). Fourier Transform Infrared Spectrometer (FTIR), and X-ray Photoelectron Spectroscopy (XPS) show that nanoparticles are stabilized by extract molecules. A growth kinetics study was performed using the Gompertz model for microorganisms exposed to nanomaterials. The results indicate that AgNPs and Au@AgNPs affect the lag phase and growth rate of Escherichia coli and Candida albicans in a dose-dependent manner, with a better response for Au@AgNPs

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