Ionization Difference between Weak and Strong Electrolytes as Perturbed by Conductivity Spectra Analysis.

While the static structure of aqueous electrolytes has been studied for decades, their dynamic microscopic structure remains unresolved yet critical in many areas. We report a comparative study of dc and ac (1 Hz to 20 GHz) conductivity data of weak and strong electrolytes, highlighting previously missing differences and similarities. Based on these results, we introduce into consideration the intrinsic short-lived ions of water, namely, excess protons (H3O+) and proton holes (OH-). We show that the model accounting for the neutralization of these ions by the species of electrolyte explains the conductivity of aqueous solutions in the concentration range 10-7-10 M. Based on independent experimental data, we hypothesize that the aggregation of the species in weak electrolytes may determine the main difference between the conductivity of weak and strong electrolytes. Our results push forward the understanding of the dynamic structure of aqueous electrolyte solutions and are important to nanofluidic, biological, and electrochemical systems.

Plasma modification of carbon nanowalls induces transition from superhydrophobic to superhydrophilic.

Graphene-based materials play an essential role in a wide range of modern technologies due to their surface properties such as adsorption capacity and controllable wettability, which depend on the production methods. For practical applications, it is crucial to control the surface properties to achieve the desired wetting characteristics, which can be described with the contact angle (CA). Here, we experimentally investigate the wettability properties of the carbon nanowalls and show how to manage a wetting transition from superhydrophobic to superhydrophilic states. A CA of 170° was reached with direct plasma synthesis, while an angle smaller than 20° was achieved during the atmosphere plasma modification. Combining the formation of the surface groups due to the plasma treatment results and the macroscale wetting behavior in terms of the Cassie-Baxter model, we qualitatively explain how the observed wetting enhancement is induced by both controlled chemical and geometrical surface-heterogeneity.

Nonrotational Mechanism of Polarization in Alcohols.

Chemical polarity governs various mechanical, chemical, and thermodynamic properties of dielectrics. Polar liquids have been amply studied, yet the basic mechanisms underpinning their dielectric properties remain not fully understood, as standard models following Debye's phenomenological approach do not account for quantum effects and cannot aptly reproduce the full dc-up-to-THz spectral range. Here, using the illustrative case of monohydric alcohols, we show that deep tunneling and the consequent intermolecular separation of excess protons and "proton-holes" in the polar liquids govern their static and dynamic dielectric properties on the same footing. We performed systematic ultrabroadband (0-10 THz) spectroscopy experiments with monohydric alcohols of different (0.4-1.6 nm) molecular lengths and show that the finite lifetime of molecular species and the proton-hole correlation length are the two principle parameters responsible for the dielectric response of all the studied alcohols across the entire frequency range. Our results demonstrate that a quantum nonrotational intermolecular mechanism drives the polarization in alcohols while the rotational mechanism of molecular polarization plays a secondary role, manifesting itself in the sub-terahertz region only.

Revealing excess protons in the infrared spectrum of liquid water.

The most common species in liquid water, next to neutral [Formula: see text] molecules, are the [Formula: see text] and [Formula: see text] ions. In a dynamic picture, their exact concentrations depend on the time scale at which these are probed. Here, using a spectral-weight analysis, we experimentally resolve the fingerprints of the elusive fluctuations-born short-living [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] ions in the IR spectra of light ([Formula: see text]), heavy ([Formula: see text]), and semi-heavy (HDO) water. We find that short-living ions, with concentrations reaching [Formula: see text] of the content of water molecules, coexist with long-living pH-active ions on the picosecond timescale, thus making liquid water an effective ionic liquid in femtochemistry.