34,453 research outputs found
Electrokinetic and hydrodynamic properties of charged-particles systems: From small electrolyte ions to large colloids
Dynamic processes in dispersions of charged spherical particles are of
importance both in fundamental science, and in technical and bio-medical
applications. There exists a large variety of charged-particles systems,
ranging from nanometer-sized electrolyte ions to micron-sized charge-stabilized
colloids. We review recent advances in theoretical methods for the calculation
of linear transport coefficients in concentrated particulate systems, with the
focus on hydrodynamic interactions and electrokinetic effects. Considered
transport properties are the dispersion viscosity, self- and collective
diffusion coefficients, sedimentation coefficients, and electrophoretic
mobilities and conductivities of ionic particle species in an external electric
field. Advances by our group are also discussed, including a novel
mode-coupling-theory method for conduction-diffusion and viscoelastic
properties of strong electrolyte solutions. Furthermore, results are presented
for dispersions of solvent-permeable particles, and particles with non-zero
hydrodynamic surface slip. The concentration-dependent swelling of ionic
microgels is discussed, as well as a far-reaching dynamic scaling behavior
relating colloidal long- to short-time dynamics
StokesâEinsteinâDebye failure in molecular orientational diffusion: exception or rule?
The StokesâEinsteinâDebye (SED) expression is used routinely to relate orientational molecular diffusivity quantitatively to viscosity. However, it is well-known that Einsteinâs equations are derived from hydrodynamic theory for the diffusion of a Brownian particle in a homogeneous fluid and examples of SED breakdown and failure for molecular diffusion are not unusual. Here, using optical Kerr-effect spectroscopy to measure orientational diffusion for solutions of guanidine hydrochloride in water and mixtures of carbon disulfide with hexadecane, we show that these two contrasting systems each show pronounced exception to the SED relation and ask if it is reasonable to expect molecular diffusion to be a simple function of viscosity
A transferable ab-initio based force field for aqueous ions
We present a new polarizable force field for aqueous ions (Li+, Na+, K+, Rb+,
Cs+, Mg2+, Ca2+, Sr2+ and Cl-) derived from condensed phase ab-initio
calculations. We use Maximally Localized Wannier Functions together with a
generalized force and dipole-matching procedure to determine the whole set of
parameters. Experimental data is then used only for validation purposes and a
good agreement is obtained for structural, dynamic and thermodynamic
properties. The same procedure applied to crystalline phases allows to
parametrize the interaction between cations and the chloride anion. Finally, we
illustrate the good transferability of the force field to other thermodynamic
conditions by investigating concentrated solutions.Comment: 31 pages, 8 figure
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How Water's Properties Are Encoded in Its Molecular Structure and Energies.
How are water's material properties encoded within the structure of the water molecule? This is pertinent to understanding Earth's living systems, its materials, its geochemistry and geophysics, and a broad spectrum of its industrial chemistry. Water has distinctive liquid and solid properties: It is highly cohesive. It has volumetric anomalies-water's solid (ice) floats on its liquid; pressure can melt the solid rather than freezing the liquid; heating can shrink the liquid. It has more solid phases than other materials. Its supercooled liquid has divergent thermodynamic response functions. Its glassy state is neither fragile nor strong. Its component ions-hydroxide and protons-diffuse much faster than other ions. Aqueous solvation of ions or oils entails large entropies and heat capacities. We review how these properties are encoded within water's molecular structure and energies, as understood from theories, simulations, and experiments. Like simpler liquids, water molecules are nearly spherical and interact with each other through van der Waals forces. Unlike simpler liquids, water's orientation-dependent hydrogen bonding leads to open tetrahedral cage-like structuring that contributes to its remarkable volumetric and thermal properties
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