Examining the Contributions of Image-Charge Forces to Charge Reversal: Discrete Versus Continuum Modeling of Surface Charges

Interaction between charged lipid vesicles and point- or rod-like trivalent ions

This work examines the influence of the charge distribution of trivalent cations on their interaction with soft anionic particles, using a combination of experimental measurements and theoretical modelling. In particular, we perform electrophoresis measurements to determine the zeta-potential of anionic liposomes in the presence of spermidine and lanthanum cations. We work in a range of electrolyte concentration where a reversal in the electrophoretic mobility of the liposomes is expected; however, unlike the case of lanthanum cations, spermidine does not induce mobility reversal of liposomes. As a result, the charge distribution within the counterion appears to be a key factor. This conclusion is supported by a theory that accounts for intra-ionic correlations, which has previously been successfully used to describe the colloidal electric double layer. It allows us to model spermidine as rod-like ions and lanthanum cations as point-like ions in order to test the importance of the ionic geometry in the interactions with soft particles such as lipid vesicles.

Efficient nano titanium electrode via a two-step electrochemical anodization with reconstructed nanotubes: Electrochemical activity and stability

A two-step anodization method was used to prepare an efficient nano Ti electrode (ENTE), based on the nano Ti electrode (NTE) that was synthesized by the traditional anodization method. The result of FESEM showed there were many nanopores and nanoparticles on the surface of the ENTE. Compared with Ti electrode, the ENTE exhibited an increased electrochemical activity of nitrate reduction, attributing to its ∼1.09-fold higher reduction peak current density. Values of average current efficiency towards nitrate reduction indicated that the electrochemical properties of different electrodes were raised in the order of ENTE (0.36) > NTE (0.25) > Ti electrode (0.15). The ENTE exhibited a ∼3.33-fold higher electroactive surface area than that of Ti electrode. The higher current density throughout the 1000 s and the ∼1.27-fold higher final current density at 1000 s suggested that the ENTE had a higher stability for nitrate electroreduction. The nitrate reduction efficiency increased with the increasing of initial nitrate-nitrogen concentration and temperature. Similar effect was obtained from current density below 50 mA cm^-2. And under the neutral condition, a higher nitrate reduction efficiency was achieved. The curved surface and higher surface area due to the nanopores of the ENTE increased the nitrate concentration in the EDL and enhanced the potential of individual nitrate ions in the diffuse layer exponentially. This research provided a new route to assess a nano-electrode with high stability and a clear reaction mechanism in EDL.

Simulations of Coulomb systems confined by polarizable surfaces using periodic Green functions

We present an efficient approach for simulating Coulomb systems confined by planar polarizable surfaces. The method is based on the solution of the Poisson equation using periodic Green functions. It is shown that the electrostatic energy arising from the surface polarization can be decoupled from the energy due to the direct Coulomb interaction between the ions. This allows us to combine an efficient Ewald summation method, or any other fast method for summing over the replicas, with the polarization contribution calculated using Green function techniques. We apply the method to calculate density profiles of ions confined between the charged dielectric and metal surfaces.

On the physics of both surface overcharging and charge reversal at heterophase interfaces

A series of Monte Carlo simulations are employed to reveal the physics of both surface overcharging and charge reversal at a negatively charged dielectric interface exposed to a bulk solution containing a +2:−1 electrolyte in the absence and presence of a monovalent salt.