Advances in Colloid and Interface Science (v.185-186, #C)

By extending the concept of an effective temperature, earlier introduced for sheared monodisperse suspensions, we propose a continuum theory for sheared bidisperse suspensions. We show the theory for sheared suspensions can be constructed from the theory for Brownian suspensions by replacing the temperature with the effective temperature. Furthermore, we explore the validity of closure relations based on mean field/free volume theory, by comparison with experimental data obtained for Brownian bidisperse suspensions. In a recent paper, we have shown that the new theory, combined with the discussed closure relations, is indeed a predictive theory.Display Omitted► An effective temperature, linear in the shear stress, explains migration in sheared suspensions. ► Non-equilibrium osmotic pressure equals effective temperature times compressibility factor. ► All closures in the theory can be formulated in terms of free volume. ► Scaling of effective temperature with shear rate depends on the particular contact force.
Keywords: Effective temperature; Slow dynamics; Sheared suspensions; Bidispersity; Non-equilibrium thermodynamics;

Electronic transfer as a route to increase the chemical stability in gold and silver core–shell nanoparticles by Derrick M. Mott; Dao Thi Ngoc Anh; Prerna Singh; Cheshta Shankar; Shinya Maenosono (14-33).
This review article presents the collected recent findings and advancements in understanding and manipulating the electronic properties of the Au/Ag NP system from the standpoint of controlling the characteristics of heterostructured core–shell NPs. The discovery of the electronic transfer effect through analysis of both Ag–Au and Au–Ag type NPs inspired the analysis of the resulting enhanced properties. First, the background on the synthesis and characterization of Ag, Au, Ag–Au, Au–Ag and Au–Ag–Au NPs, which will be used as a basis for studying the electronic transfer and stability properties is presented. Next, Mie Theory is used to inspect the optical properties of the Ag–Au NPs, revealing subtle structural characteristics in these probes, which has implications to the plasmonic properties. This is followed by the inspection of the electronic properties of the Au–Ag NPs primarily through XPS and XANES analysis, revealing the origins of the electronic transfer phenomenon. The unique electronic properties are then revealed to result in improved particle stability in terms of susceptibility to oxidation. Finally, an assessment of the resulting enhanced plasmonic sensing properties is discussed. The results are presented in terms of synthesis technique, material characterization, understanding of the electronic properties and manipulation of those properties to create Au–Ag NPs with enhanced resistance to oxidation and galvanic replacement.Display Omitted► Electronic transfer in gold and silver nanoparticle probes has been demonstrated. ► The electronic transfer phenomenon causes the silver to become electron rich. ► In Au–Ag nanoparticles, the electron rich silver layer becomes oxidation resistant. ► The study reveals highly active and robust plasmonic sensing and diagnostic probes.
Keywords: Gold; Silver; Core/shell; Electronic transfer; Plasmonic;

Towards a description of particulate fouling: From single particle deposition to clogging by Christophe Henry; Jean-Pierre Minier; Grégory Lefèvre (34-76).
Particulate fouling generally arises from the continuous deposition of colloidal particles on initially clean surfaces, a process which can even lead to a complete blockage of the fluid cross-section. In the present paper, the initial stages of the fouling process (which include single-particle deposition and reentrainment) are first addressed and current modelling state-of-the-art for particle–turbulence and particle–wall interactions is presented. Then, attention is specifically focused on the later stages (which include multilayer formation, clogging and blockage). A detailed review of experimental works brings out the essential mechanisms occurring during these later stages: as for the initial stages, it is found that clogging results from the competition between particle–fluid, particle–surface and particle–particle interactions. Numerical models that have been proposed to reproduce the later stages of fouling are then assessed and a new Lagrangian stochastic approach to clogging in industrial cases is detailed. These models further confirm that, depending on hydrodynamical conditions (the flow velocity), fluid characteristics (such as the ionic strength) as well as particle and substrate properties (such as zeta potentials), particle deposition can lead to the formation of either a single monolayer or multilayers. The present paper outlines also future numerical developments and experimental works that are needed to complete our understanding of the later stages of the fouling process.Display Omitted► Review of the experimentally-identified mechanisms of monolayer/multilayer formation. ► Review of numerical models proposed to model clogging. ► Proposal of a new modelling approach to model clogging in industrial cases. ► Discussion on future trends to complete our knowledge of clogging.
Keywords: Colloid; Particle; Fouling; Clogging; DLVO; Lagrangian;