A possibility for the observation of so-called structure resonances (SR) in electrolytes arising due to relative motion of the cluster charged nucleus and its solvation shell is demonstrated. The discussed method considers the resonant contribution of the SR to the frequency dependence of the reflection (transmission) coefficient of the electromagnetic wave interacting with the free electrolyte surface. Of special interest is the observation of SR for multiply charged particles in electrolyte providing direct information on the charge of single cluster. Also important are other not so prominent details of the wave interaction with mobile charged clusters in electrolyte related to the formation and complicated nature of the frequency dependence of the charged cluster associated mass.
We present an improved approach to the impedance spectroscopy of conductive liquid samples using four-electrode measurements. Our method enables impedance measurements of conductive liquids down to the sub-Hertz frequencies, avoiding the electrode polarization effects that usually cripple standard impedance analysers. We have successfully tested our apparatus with aqueous solutions of potassium chloride and gelatin. The first substance has shown flat spectra from $sim$100 kHz down to sub-Hz range, while the results on gelatin clearly show the existence of two distinct low frequency conductive relaxations.
We study the excess free energy due to phase coexistence of fluids by Monte Carlo simulations using successive umbrella sampling in finite LxLxL boxes with periodic boundary conditions. Both the vapor-liquid phase coexistence of a simple Lennard-Jones fluid and the coexistence between A-rich and B-rich phases of a symmetric binary (AB) Lennard-Jones mixture are studied, varying the density rho in the simple fluid or the relative concentration x_A of A in the binary mixture, respectively. The character of phase coexistence changes from a spherical droplet (or bubble) of the minority phase (near the coexistence curve) to a cylindrical droplet (or bubble) and finally (in the center of the miscibility gap) to a slab-like configuration of two parallel flat interfaces. Extending the analysis of M. Schrader, P. Virnau, and K. Binder [Phys. Rev. E 79, 061104 (2009)], we extract the surface free energy gamma (R) of both spherical and cylindrical droplets and bubbles in the vapor-liquid case, and present evidence that for R -> Infinity the leading order (Tolman) correction for droplets has sign opposite to the case of bubbles, consistent with the Tolman length being independent on the sign of curvature. For the symmetric binary mixture the expected non-existence of the Tolman length is confirmed. In all cases {and for a range of radii} R relevant for nucleation theory, gamma(R) deviates strongly from gamma (Infinity) which can be accounted for by a term of order gamma(Infinity)/gamma(R)-1 ~ 1/R^2. Our results for the simple Lennard-Jones fluid are also compared to results from density functional theory and we find qualitative agreement in the behavior of gamma(R) as well as in the sign and magnitude of the Tolman length.
We report on the capillary-driven levelling of a topographical perturbation at the surface of a free-standing liquid nanofilm. The width of a stepped surface profile is found to evolve as the square root of time. The hydrodynamic model is in excellent agreement with the experimental data. In addition to exhibiting an analogy with diffusive processes, this novel system serves as a precise nanoprobe for the rheology of liquids at interfaces in a configuration that avoids substrate effects.
The properties of liquid dispersions, such as foams or emulsions, depend strongly on the volume fraction $phi$ of the continuous phase. Concentrating on the example of foams, we show experimentally and theoretically that $phi$ may be related to the fraction $phi_s$ of the surface at a wall which is wetted by the continuous phase - given an expression for the interfacial energy or osmotic pressure of the bulk system. Since the surface fraction $phi_s$ can be readly determined from optical measurement and since there are good general approximations available for interfacial energy and osmotic pressure we thus arrive at an advantageous method of estimating $phi$. The same relationship between $phi$ and $phi_s$ is also expected to provide a good approximation of the fraction of the bubble or drop surface which is wetted by the continuous phase. This is a parameter of great importance for the rheology and ageing of liquid dispersions.
Ion-pairing is commonly considered as a culprit for the reduced ionic conductivity in polymer electrolyte systems. However, this simple thermodynamic picture should not be taken literally, as ion-pairing is a dynamical phenomenon. Here we construct model PEO-LiTFSI systems with different degree of ion-pairing by tuning solvent polarity, and examine the relation between the cation-anion distinct conductivity $sigma^rm{d}_{+-}$ and the lifetime of ion-pairs $tau_{+-}$ using molecular dynamics simulations. It is found that there exist two distinct regimes where $sigma^rm{d}_{+-}$ scales with $1/tau_{+-}$ and $tau_{+-}$ respectively, and the latter is a signature of longer-lived ion-pairs which contribute negatively to the total ionic conductivity. This suggests that ion-pairs are kinetically different depending on the solvent polarity, which renders the ion-pair lifetime highly important when discussing its effect on ion transport in polymer electrolyte systems.