Refractive-index gas thermometry.

The principles and techniques of primary refractive-index gas thermometry (RIGT) are reviewed. Absolute primary RIGT using microwave measurements of helium-filled quasispherical resonators has been implemented at the temperatures of the triple points of neon, oxygen, argon and water, with relative standard uncertainties ranging from 9.1 × 10 to 3.

Progress towards the determination of thermodynamic temperature with ultra-low uncertainty.

Previous research effort towards the determination of the Boltzmann constant has significantly improved the supporting theory and the experimental practice of several primary thermometry methods based on the measurement of a thermodynamic property of a macroscopic system at the temperature of the triple point of water. Presently, experiments are under way to demonstrate their accuracy in the determination of the thermodynamic temperature T over an extended range spanning the interval between a few kelvin and the copper freezing point (1358 K). We discuss how these activities will improve the link between thermodynamic temperature and the temperature as measured using the International Temperature Scale of 1990 (ITS-90) and report some preliminary results obtained by dielectric constant gas thermometry and acoustic gas thermometry.

Second osmotic virial coefficient from the two-component van der Waals equation of state.

The second osmotic virial coefficient is in principle obtained from the second-order term in the expansion of the osmotic pressure Π or solute activity z(2) in powers of the solute density ρ(2) at fixed solvent activity z(1) and temperature T. It is remarked that the second-order terms in the analogous expansions at fixed pressure p or at liquid-vapor coexistence instead of at fixed z(1) also provide measures of the effective, solvent-mediated solute-solute interactions, but these are different measures. It is shown here how the function z(2)(ρ(2), z(1), T) required to obtain the second osmotic virial coefficient B from an expansion in ρ(2) may be obtained from an equation of state of the form p = p(ρ(1), ρ(2), T) with ρ(1) the solvent density, and also how the analogous coefficient B' in the fixed-p expansion may be so obtained.

Communication: Length scale dependent oil-water energy fluctuations.

Interfacial fluctuations in the cohesive (van der Waals) interaction energy of spherical oil-drops with water provide evidence of a length scale dependent transition from linear to non-linear response behavior. For sub-nanometer oil-drop sizes, energy fluctuations are found to be independent of the van der Waals coupling strength, while nanometer (and larger) size oil drops experience highly non-linear energy fluctuations. The latter behavior is linked to enhanced hydrophobic density fluctuations and the emergence of entropic contributions to oil-water cohesive interaction free energies.

Are long-chain alkanes hydrophilic?

Although short n-alkane chains are classic examples of hydrophobic solutes, mounting evidence points to a hydrophilic crossover for the hydration free energies (DeltaG) of sufficiently long n-alkane chains. Experimental and simulation results for the hydration of n-alkanes from methane (C1) to docosane (C22) are combined with fundamental thermodynamic relations to elucidate intermolecular contributions to DeltaG. Theoretical bounds on the influence of solute conformation on DeltaG are inferred by considering the hydration of idealized linear (all-trans) and globular (spherical) model solutes.

Unraveling water's entropic mysteries: a unified view of nonpolar, polar, and ionic hydration.

[Figure: see text]. Most chemical processes on earth are intimately linked to the unique properties of water, relying on the versatility with which water interacts with molecules of varying sizes and polarities. These interactions determine everything from the structure and activity of proteins and living cells to the geological partitioning of water, oil, and minerals in the Earth's crust.