Reversible Transient Nucleation in Ionic Solutions as the Precursor of Ion Crystallization

Molecular dynamics simulations for aqueous sodium chloride solutions were carried out at various concentrations. Supplementary to the Debye-H\"uckel theory, reversible transient nucleation of ions was observed even in dilute solutions. The average size of formed ion clusters and the lifetime of ion pairs increase with concentration until the saturation point, when ion clusters become stable and individual ions adjust their positions to form ordered lattice structures, leading to irreversible ion crystallization, which is beyond the description of the classical nucleation theory.Comment: 4 pages, 5 figures, and 46 reference

One-step hydrothermal synthesis of fluorescence carbon quantum dots with high product yield and quantum yield

A one-step hydrothermal synthesis of nitrogen and silicon co-doped fluorescence carbon quantum dots (N,Si-CQDs), from citric acid monohydrate and silane coupling agent KH-792 with a high product yield (PY) of 52.56% and high quantum yield (QY) of 97.32%, was developed. This greatly improves both the PY and QY of CQDs and provides a new approach for a large-scale production of high-quality CQDs. Furthermore, N,Si-CQDs were employed as phosphors without dispersants to fabricate white light-emitting diodes (WLEDs) with the color coordinates at (0.29, 0.32). It is suggested that N,Si-CQDs have great potential as promising fluorescent materials to be applied in WLEDs.Peer reviewe

Microscopic structure and dynamics of air/water interface by computer simulations-comparison with sum-frequency generation experiments

The air/water interface was simulated and the mode amplitudes and their ratios of the effective nonlinear sum-frequency generation (SFG) susceptibilities (A_(eff)'s) were calculated for the ssp, ppp, and sps polarization combinations and compared with experiments. By designating “surface-sensitive” free OH bonds on the water surface, many aspects of the SFG measurements were calculated and compared with those inferred from experiment. We calculate an average tilt angle close to the SFG observed value of 35, an average surface density of free OH bonds close to the experimental value of about 2.8 × 10^(18) m^(−2), computed ratios of A_(eff)'s that are very similar to those from the SFG experiment, and their absolute values that are in reasonable agreement with experiment. A one-parameter model was used to calculate these properties. The method utilizes results available from independent IR and Raman experiments to obtain some of the needed quantities, rather than calculating them ab initio. The present results provide microscopic information on water structure useful to applications such as in our recent theory of on-water heterogeneous catalysis

Thermal Stabilities of Two-Dimensional Ball-Stick Polygons: A Critical Edge Number

Phase behaviors of two-dimensional (2D) systems locate as a fundamental topic in condensed matter and statistical physics. Although hard polygons and interactive point-like particles are well studied, the phase behaviors of more realistic molecular systems containing intermolecular interaction and molecular shape remain elusive. Here we investigate by molecular dynamics simulation thermal stabilities of 2D ball-stick polygons, serving as simplified models for molecular systems. Below the melting temperature $T_{m}$, we identify a critical edge number $n_{c}$, at which a waving superlattice structure emerges; when n < $n_{c}$,the triangular system stabilizes at a spin-ice-like glassy state; when n > $n_{c}$,the polygons stabilize at crystalline states, and $T_{m}$ is higher for polygons with more edges at higher pressures but exhibits a crossover for hexagon and octagon at low pressures. A theoretical framework considering the competition between entropy and enthalpy is proposed to provide a comprehensive understanding of our results, which is anticipated to facilitate the design of 2D materials