المؤلفون: Jedlovszky, Pál, Sega, Marcello

المصدر: Journal of Chemical Physics; 5/28/2024, Vol. 160 Issue 20, p1-4, 4p

مصطلحات موضوعية: VISCOSITY, LIQUID surfaces, INTERFACE dynamics, ATMOSPHERIC chemistry, MOLECULAR dynamics, DISPERSION relations

مستخلص: The precise determination of surface transport coefficients at liquid interfaces is critical to an array of processes, ranging from atmospheric chemistry to catalysis. Building on our prior results that highlighted the emergence of a greatly reduced surface viscosity in simple liquids via the dispersion relation of surface excitations [Malgaretti et al., J. Chem. Phys. 158, 114705 (2023)], this work introduces a different approach to directly measure surface viscosity. We use modified Green–Kubo relations suitable for inhomogeneous systems to accurately quantify viscosity contributions from fluid slabs of variable thickness through extensive molecular dynamics simulations. This approach distinguishes the viscosity effects of the surface layer vs the bulk, offering an independent measure of surface viscosity and providing a more detailed understanding of interfacial dynamics and its transport coefficients. [ABSTRACT FROM AUTHOR]

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المؤلفون: Ouyang, Yubing, Liu, Yanming, Fan, Yujian, Zhou, Yang, Shi, Tao

المصدر: Journal of Chemical Physics; 4/7/2024, Vol. 160 Issue 13, p1-9, 9p

مصطلحات موضوعية: COHESION, SALINITY, WATER salinization, MOLECULAR dynamics, SOIL cohesion, SOIL mineralogy, LIQUID surfaces, QUARTZ

مستخلص: The moisture with salt ions adsorbed on the mineral soil surface is crucial to the cohesion process when the media is exposed to marine or coastal environments. However, the impact of salinity on the cohesion of soils is not well studied at the nanoscale. In this study, the salinity effect was investigated by studying the wettability and capillary force of NaCl solutions on quartz substrates via a molecular dynamics-based approach. Besides, a new visualization method was proposed to measure the contact angle of liquid droplets from the aspect of nanoscale. The results indicated that salt ions can weaken the wettability of the liquid on the quartz surface and inhibit the capillary force. Compared with water, the liquid with a 10% NaCl solution can achieve a capillary force reduction of around 70%, resulting in a detrimental effect on the cohesion of soils. Overall, this study enhanced the understanding of the nanoscale salinity effect on the cohesion process and provided insights into the modification of the mechanical properties of soils from the aspect of nanoscale. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Chemical Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Yamaguchi, Shoichi, Takayama, Tetsuyuki, Otosu, Takuhiro

المصدر: Journal of Chemical Physics; 11/7/2023, Vol. 159 Issue 17, p1-6, 6p

مصطلحات موضوعية: PHOTON upconversion, LIQUID surfaces, SURFACE tension

مستخلص: In view of the current situation in which non-polarizable rigid water models have been scarcely examined against surface-specific properties, we appraise TIP4P-type models at the liquid water surface on the basis of heterodyne-detected sum frequency generation (HD-SFG) spectroscopy. We find in the HD-SFG spectrum of the water surface that the peak frequency of the hydrogen-bonded OH band, the half width at half maximum of the hydrogen-bonded OH band, and the full width at half maximum of the free OH band are best reproduced by TIP4P, TIP4P/Ew, and TIP4P/Ice, respectively, whereas it is already well known that TIP4P/2005 best reproduces the surface tension. These TIP4P-type models perform better at the water surface in terms of the present appraisal items than some polarizable models in the literature. [ABSTRACT FROM AUTHOR]

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المؤلفون: Vuković, F., Garcia, N. A., Perera, S., Turchi, M., Andersson, M. P., Solvang, M., Raiteri, P., Walsh, T. R.

المصدر: Journal of Chemical Physics; 9/14/2023, Vol. 159 Issue 10, p1-11, 11p

مصطلحات موضوعية: CALCIUM, MOLECULAR dynamics, STONE, WOOL, MINERAL wool, GLASS fibers, LIQUID surfaces

مستخلص: The dissolution behavior of calcium aluminosilicate based glass fibers, such as stone wool fibers, is an important consideration in mineral wool applications for both the longevity of the mineral wool products in humid environments and limiting the health impacts of released and inhaled fibers from the mineral wool product. Balancing these factors requires a molecular-level understanding of calcium aluminosilicate glass dissolution mechanisms, details that are challenging to resolve with experiment alone. Molecular dynamics simulations are a powerful tool capable of providing complementary atomistic insights regarding dissolution; however, they require force fields capable of describing not-only the calcium aluminosilicate surface structure but also the interactions relevant to dissolution phenomena. Here, a new force field capable of describing amorphous calcium aluminosilicate surfaces interfaced with liquid water is developed by fitting parameters to experimental and first principles simulation data of the relevant oxide-water interfaces, including ab initio molecular dynamics simulations performed for this work for the wüstite and periclase interfaces. Simulations of a calcium aluminosilicate surface interfaced with liquid water were used to test this new force field, suggesting moderate ingress of water into the porous glass interface. This design of the force field opens a new avenue for the further study of calcium and network-modifier dissolution phenomena in calcium aluminosilicate glasses and stone wool fibers at liquid water interfaces. [ABSTRACT FROM AUTHOR]

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المؤلفون: Hemauer, Felix, Krappmann, Daniel, Schwaab, Valentin, Hussain, Zarah, Freiberger, Eva Marie, Waleska-Wellnhofer, Natalie J., Franz, Evanie, Hampel, Frank, Brummel, Olaf, Libuda, Jörg, Hirsch, Andreas, Steinrück, Hans-Peter, Papp, Christian

المصدر: Journal of Chemical Physics; 8/21/2023, Vol. 159 Issue 7, p1-15, 15p

مصطلحات موضوعية: ENERGY storage, ESTER derivatives, SOLAR thermal energy, LIQUID surfaces, HEAT storage, PHOTOCHEMICAL smog, RENEWABLE energy sources, RENEWABLE energy transition (Government policy), CARBONACEOUS aerosols

مستخلص: The transition to renewable energy sources comes along with the search for new energy storage solutions. Molecular solar thermal systems directly harvest and store solar energy in a chemical manner. By a suitable molecular design, a higher overall efficiency can be achieved. In this study, we investigate the surface chemistry of oxa-norbornadiene/quadricyclane derivatives on a Pt(111) surface. Specifically, we focus on the energy storage and release properties of molecules that are substituted with ester moieties of different sizes. For our model catalytic approach, synchrotron radiation-based x-ray photoelectron spectroscopy measurements were conducted in ultra-high vacuum (UHV) and correlated with the catalytic behavior in the liquid phase monitored by photochemical infrared reflection absorption spectroscopy. The differences in their spectral appearance enabled us to unambiguously differentiate the energy-lean and energy-rich isomers and decomposition products. Next to qualitative information on the adsorption motifs, temperature-programmed experiments allowed for the observation of thermally induced reactions and the deduction of the related reaction pathways. We analyzed the selectivity of the cycloreversion reaction from the energy-rich quadricyclane derivative to its energy-lean norbornadiene isomer and competing processes, such as desorption and decomposition. For the 2,3-bis(methylester)-substitution, the cycloreversion reaction was found to occur between 310 and 340 K, while the thermal stability limit of the compounds was determined to be 380 K. The larger 2,3-bis(benzylester) derivatives have a lower apparent adsorption energy and a decomposition onset already at 135 K. In the liquid phase (in acetonitrile), we determined the rate constants for the cycloreversion reaction on Pt(111) to k = 5.3 × 10⁻⁴ s⁻¹ for the 2,3-bis(methylester)-substitution and k = 6.3 × 10⁻⁴ s⁻¹ for the 2,3-bis(benzylester) derivative. The selectivities were of >99% and 98% for the two molecules, respectively. The difference in the catalytic behavior of Pt(111) for both derivatives is less pronounced in the liquid phase than in UHV, which we attribute to the passivation of the Pt(111) surface by carbonaceous species under ambient conditions. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Chemical Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Yang, Walt, Lee, Chin, Saric, Steven, Pohl, Marvin N., Neumark, Daniel M.

المصدر: Journal of Chemical Physics; 8/7/2023, Vol. 159 Issue 5, p1-10, 10p

مصطلحات موضوعية: ANGULAR distribution (Nuclear physics), THERMAL desorption, LIQUID surfaces, MOMENTUM transfer, MOLECULAR beams

مستخلص: The evaporation and scattering of Ne, CD4, and D2O from a dodecane flat liquid jet are investigated in a molecular beam apparatus. The experiment yields translational energy distributions as a function of scattering angle by means of a rotatable mass spectrometer. In the evaporation experiments, one observes a Maxwell–Boltzmann distribution with a cos θ angular distribution superimposed on a weak, isotropic background. The scattering experiments show contributions from impulsive scattering and thermal desorption. At select incident angles for the three systems, angular distributions show super-specular scattering for the impulsive scattering channel, an effect attributed to anisotropic momentum transfer to the liquid surface. The impulsive scattering channel is analyzed with a soft-sphere model to explore energy transfer between the scatterer and liquid as a function of deflection angle. Compared to Ne scattering, the polyatomic gases exhibit more thermal desorption and, in the impulsive scattering channel, a higher degree of internal excitation. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Chemical Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Peng, Hsuan-Yi, Liu, Bang-Yan, Lo, Chi-Chun, Chen, Li-Jen, Seemann, Ralf, Brinkmann, Martin

المصدر: Journal of Chemical Physics; 7/14/2023, Vol. 159 Issue 2, p1-10, 10p

مصطلحات موضوعية: CAPILLARY flow, LIQUID surfaces, WETTING, LIQUID films, SYMMETRY breaking

مستخلص: Directional wicking and spreading of liquids can be achieved by regular micro-patterns of specifically designed topographic features that break the reflection symmetry of the underlying pattern. The present study aims to understand the formation and stability of wetting films during the evaporation of volatile liquid drops on surfaces with a micro-pattern of triangular posts arranged in a rectangular lattice. Depending on the density and aspect ratio of the posts, we observe either spherical-cap shaped drops with a mobile three-phase contact line or the formation of circular or angular drops with a pinned three-phase contact line. Drops of the latter class eventually evolve into a liquid film extending to the initial footprint of the drop and a shrinking cap-shaped drop sitting on the film. The drop evolution is controlled by the density and aspect ratio of the posts, while no influence of the orientation of the triangular posts on the contact line mobility becomes evident. Our experiments corroborate previous results of systematic numerical energy minimization, predicting that conditions for a spontaneous retraction of a wicking liquid film depend weakly on the orientation of the film edge relative to the micro-pattern. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Chemical Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Roman, Maksymilian J., Knight, Adam G., Moon, Daniel R., Lane, Paul D., Greaves, Stuart J., Costen, Matthew L., McKendrick, Kenneth G.

المصدر: Journal of Chemical Physics; 6/28/2023, Vol. 158 Issue 24, p1-15, 15p

مصطلحات موضوعية: ANGULAR distribution (Nuclear physics), MONOMOLECULAR films, LIQUID surfaces, PLANAR laser-induced fluorescence, MOLECULAR dynamics, MONTE Carlo method

مستخلص: Inelastic collisions of OH with an inert liquid perfluoropolyether (PFPE) surface have been studied experimentally. A pulsed molecular beam of OH with a kinetic energy distribution peaking at 35 kJ mol⁻¹ was directed at a continually refreshed PFPE surface. OH molecules were detected state-selectively with spatial and temporal resolution by pulsed, planar laser-induced fluorescence. The scattered speed distributions were confirmed to be strongly superthermal, regardless of the incidence angle (0° or 45°). Angular scattering distributions were measured for the first time; their reliability was confirmed through extensive Monte Carlo simulations of experimental averaging effects, described in Paper II [A. G. Knight et al., J. Chem. Phys. 158, 244705 (2023)]. The distributions depend markedly on the incidence angle and are correlated with scattered OH speed, consistent with predominantly impulsive scattering. For 45° incidence, the angular distributions are distinctly asymmetric to the specular side but peak at sub-specular angles. This, along with the breadth of the distributions, is incompatible with scattering from a surface that is flat on a molecular scale. New molecular dynamics simulations corroborate the roughness of the PFPE surface. A subtle but unexpected systematic dependence of the angular distribution on the OH rotational state was found, which may be dynamical in origin. The OH angular distributions are similar to those for kinematically similar Ne scattering from PFPE and hence not strongly perturbed by OH being a linear rotor. The results here are broadly compatible with prior predictions from independent quasiclassical trajectory simulations of OH scattering from a model-fluorinated self-assembled monolayer surface. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Chemical Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Carrete, Jesús, Montes-Campos, Hadrián, Wanzenböck, Ralf, Heid, Esther, Madsen, Georg K. H.

المصدر: Journal of Chemical Physics; 5/28/2023, Vol. 158 Issue 20, p1-18, 18p

مصطلحات موضوعية: ACTIVE learning, LIQUID surfaces, MACHINE learning, FORCE & energy, IONIC liquids

مستخلص: A reliable uncertainty estimator is a key ingredient in the successful use of machine-learning force fields for predictive calculations. Important considerations are correlation with error, overhead during training and inference, and efficient workflows to systematically improve the force field. However, in the case of neural-network force fields, simple committees are often the only option considered due to their easy implementation. Here, we present a generalization of the deep-ensemble design based on multiheaded neural networks and a heteroscedastic loss. It can efficiently deal with uncertainties in both energy and forces and take sources of aleatoric uncertainty affecting the training data into account. We compare uncertainty metrics based on deep ensembles, committees, and bootstrap-aggregation ensembles using data for an ionic liquid and a perovskite surface. We demonstrate an adversarial approach to active learning to efficiently and progressively refine the force fields. That active learning workflow is realistically possible thanks to exceptionally fast training enabled by residual learning and a nonlinear learned optimizer. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Chemical Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Yu, Zhiyong, Lv, Songtai, Zhang, Xin, Liang, Hongtao, Xie, Wei, Yang, Yang

المصدر: Journal of Chemical Physics; 5/14/2023, Vol. 158 Issue 18, p1-10, 10p

مصطلحات موضوعية: LIQUID-vapor interfaces, SURFACE tension, LIQUID surfaces, LASER pulses, LEAD, CYCLIC codes, HILBERT-Huang transform

مستخلص: We demonstrate a methodology for computationally investigating the mechanical response of a pure molten lead surface system to the lateral mechanical cyclic loads and try to answer the following question: how does the dynamically driven liquid surface system follow the classical physics of the elastic-driven oscillation? The steady-state oscillation of the dynamic surface tension (or excess stress) under cyclic load, including the excitation of high-frequency vibration mode at different driving frequencies and amplitudes, was compared with the classical theory of a single-body driven damped oscillator. Under the highest studied frequency (50 GHz) and amplitude (5%) of the load, the increase of in (mean value) dynamic surface tension could reach ∼5%. The peak and trough values of the instantaneous dynamic surface tension could reach (up to) 40% increase and (up to) 20% decrease compared to the equilibrium surface tension, respectively. The extracted generalized natural frequencies seem to be intimately related to the intrinsic timescales of the atomic temporal–spatial correlation functions of the liquids both in the bulk region and in the outermost surface layers. These insights uncovered could be helpful for quantitative manipulation of the liquid surface using ultrafast shockwaves or laser pulses. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Chemical Physics is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)