Lipase activity and stability in ionic liquids containing N,N-dialkylimidazolium cations and different anions were investigated in alcoholysis reactions.
We present a classical molecular-dynamics study of the collective dynamical properties of the coexisting liquid phase at equilibrium body-centered cubic (BCC) Fe crystal-melt interfaces. For the three interfacial orientations (100), (110), and (111), the collective dynamics are characterized through the calculation of the intermediate scattering functions, dynamical structure factors and density relaxation times in a sequential local region of interest. An anisotropic speed up of the collective dynamics in all three BCC crystal-melt interfacial orientations is observed. This trend differs significantly different from the previously observed slowing down of the local collective dynamics at the liquid-vapor interface [Acta Mater 2020;198:281]. Examining the interfacial density relaxation times, we revisit the validity of the recently developed time-dependent Ginzburg-Landau (TDGL) theory for the solidification crystal-melt interface kinetic coefficients, resulting in excellent agreement with both the magnitude and the kinetic anisotropy of the CMI kinetic coefficients measured from the non-equilibrium MD simulations.
The direct measurement of the dielectric properties of the confined water is exceedingly challenging, result in the lack of a quantitative understanding of its critical roles in electrochemistry, interfacial reactivity and transport thermodynamics. In this paper, we employ the equilibrium molecular dynamics simulation and the linear response theory-based analytical expressions for the local permittivity tensor, to calculate the static and dynamic dielectric response properties of the monolayer ice and water confined in the 0.65 nm size hydrophobic slab pore under 5×10 8 Pa lateral pressure and different temperatures. We carry out a detailed comparative study on the performance of predicting the confined structure and dielectric response properties between two well known water molecule models, i.e., constant dipole moment SPC/E model and polarizable SWM4-NDP water model. We have analyzed the probability distributions of the instantaneous SWM4-NDP water molecular dipole moments and calculated the static structure factor, radial dipole-dipole correlation function, static dielectric tensor, total dipole autocorrelation function and Debye relaxation time of each simulation system. For the first time, we found the novel variation of the water molecular polarities, in the monolayer confined liquid and solid phase of water, due to the extreme confinement condition. The performance in describing the structural properties are found comparable between the two water models, and the enhancement of the confinement weakens the advantage of the SWM4-NDP model in predicting the static dielectric property. However, in the prediction of the dynamic properties such as dielectric relaxation time, SWM4-NDP water model is superior to the SPC/E model. Therefore, we suggest that using SWM4-NDP model in the future investigation of the structural phase transition kinetics, ionic transportation and solvation kinetics would be the better choice. The current achievement of the fundamental insight and computational data could potentially facilitate the theoretical advancements in designing new devices of energy storage, sensor, and medicine delivery based on confined water systems.
The ice-water interface's kinetics has long been paid much attention because of its central role in ice nucleation, growth and surface/interface melting. However, there exist few studies focused on the kinetics of the confined ice-water interface. In this paper, we employ the equilibrium molecular dynamics simulation and the phase equilibrium technique for the confined water and ice to study the 1D crystal-melt coexistence line of an equilibrium mono-layer ice-water coexistence system, described by two well-known water molecule models, i.e., constant dipole moment TIP4P/2005 model and polarizable SWM4-NDP water model. The mono-layer ice-water phase equilibria are confined in the hydrophobic slab pore of 0.65 nm, under 0.5 GPa lateral pressure. By tracking the 1D ice-water coexistence line's position, we calculate the power spectrum of the equilibrium line fluctuation and the time-dependent autocorrelation function of the line fluctuation Fourier amplitudes and then calculate a series of kinetic properties of the 1D crystal-melt coexistence line. We demonstrate that the processes involved in the relaxation of the crystal-melt coexistence line fluctuation with long wavelengths are coupled with a fast and a slow decay process characterized by two distinct time scales, while just the slow decay processes dominate the crystal-melt coexistence line fluctuation with short wavelengths. By comparing with bulk ice-water interface systems, we find that the high-frequency processes such as Rayleigh waves participate more in the relaxation of the 1D crystal-melt coexistence line fluctuation. We see that the wave vector dependence of the characteristic relaxation time (of the crystal-melt line fluctuation) is consistent with the crystal-melt interface's existing kinetic theory. Nevertheless, the characteristic relaxation time of the 1D crystal-melt coexistence line relaxation is around one order of magnitude lower than that of the 2D bulk ice-water interface system. We calculate the kinetic coefficients of the 1D crystal-melt coexistence line for the two water model systems, compare with the bulk interface systems, and find the kinetic coefficient of the confined ice-water (crystal-melt) coexistence line is much higher than that of the bulk ice-water interface system. The significant increase in the magnitude of the kinetic coefficient of the confined 1D ice-water coexistence line system may be understood by the substantial suppression of the rotational degree of freedom of the confined water molecules. The current achievement of the fundamental insight and simulation results could potentially facilitate the theoretical advancements in designing new devices of ultrafast phase-change (energy storage, sensor) devices based on confined water systems.
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