| 1. |
- An, Rong, et al.
(författare)
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Friction of Ionic Liquid–Glycol Ether Mixtures at Titanium Interfaces : Negative Load Dependence
- 2018
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Ingår i: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 5:14
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Tidskriftsartikel (refereegranskat)abstract
- Structural reorientation of alkyl chains in the phosphonium cation of orthoborate ionic liquid mixed with glycol ether occurs with increasing normal load of the AFM tip. The flat reoriented structure, similar to the ‘blooming lotus leaf’, produces a new sliding interface that is responsible for the observed lower friction at higher loads. This work is reported by Rong An, Liangliang Huang, Faiz Ullah Shah and co‐workers in article number 1800263.
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| 2. |
- An, Rong, et al.
(författare)
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Friction of Ionic Liquid–Glycol Ether Mixtures at Titanium Interfaces : Negative Load Dependence
- 2018
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Ingår i: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 5:14
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Tidskriftsartikel (refereegranskat)abstract
- The atomic force microscopy experiments and nonequilibrium molecular dynamics (NEMD) simulations demonstrate a negative friction–load dependence to ionic liquid–glycol ether mixtures, that is, the friction decreases as the normal load increases. NEMD simulations reveal a structural reorientation of the studied ionic liquid (IL): as the normal load increases, the cation alkyl chains of ILs change the orientation to preferentially parallel to the tip scanning path. The flat‐oriented IL structures, similar to the “blooming lotus leaf,” produce a new sliding interface and reduce the friction. A further molecular dynamics simulation is carried out by adopting slit‐pore models to mimic the tip approaching process to confirm the dynamics of ILs. A faster diffusion of ILs in the smaller slit pore is observed. The faster diffusion of ILs in the more confined slit pore facilitates the structural reorientation of ILs. The resulted new sliding surface is responsible for the observed smaller friction at higher loads, also known as the negative friction–load dependence. These findings provide a fundamental explanation to the role of ILs in interfacial lubrications. They help to understand liquid flow properties under confinement, with implications for the development of better nanofluidic devices.
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| 3. |
- Cao, Jian, et al.
(författare)
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Heterogeneous consecutive reaction kinetics of direct oxidation of H2 to H2O2: Effect and regulation of confined mass transfer
- 2023
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Ingår i: Chemical Engineering Journal. - : Elsevier. - 1385-8947 .- 1873-3212. ; 455
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Tidskriftsartikel (refereegranskat)abstract
- Porous catalysts in heterogeneous reactions have played an important role in the modern chemical industry, but it is still challenging to quantitatively describe mass transfer and surface reaction behaviors of reactants in nano-confined space. Direct synthesis of hydrogen peroxide (H2O2) is considered as an attractive alternative to anthraquinone oxidation process, while the confined mass transfer of H2O2 in porous catalysts limits the reactivity. In this work, taking the consecutive reaction of H2O2 synthesis as an example, a quantitative method in modeling the effects of confined mass transfer on the reactivity was studied. More specifically, calorimetry was developed to characterize the confined structures of porous carbon experimentally, the linear nonequilibrium thermodynamics and the statistical mechanics method were further combined. Then, the heterogeneous consecutive reaction kinetics and the Thiele modulus influenced by confined mass transfer were modeled. Consequently, regulation strategies were proposed with the help of theoretical models. The optimized catalyst with biological skeleton carbon support and 0.5 wt% palladium loading shows an excellent catalytic performance. Lastly, for the mesoscience in heterogeneous reaction, the resistance was explored as a quantitative descriptor to compromise in the competition between mass transfer and surface reaction. The mesoscale structures were considered as the dynamic spatiotemporal distribution of substance concentrations, and the resistance minimization multi-scale (RMMS) model was proposed.
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| 4. |
- Gao, Qingwei, et al.
(författare)
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Effect of water concentration on the microstructures of choline chloride/urea (1:2) /water mixture
- 2018
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Ingår i: Fluid Phase Equilibria. - : Elsevier. - 0378-3812 .- 1879-0224. ; 470, s. 134-139
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics was utilized to investigate the properties of ChCl/urea (1:2)/water mixtures from pure ChCl/urea to infinitely dilute solution. To further study the mechanism at molecular scale, the local microstructure variation in the mixtures with the increase of water content was analyzed in detail. Simulation results showed that neither choline cations nor chloride anions are saturated by the coordinated water molecules, even when the water molar fraction reaches 0.9. The hydration number proportions for different ions indicated that the hydration strength of chloride anion is stronger than that of choline cation, which may play greater effects on the properties of mixtures. This result is further confirmed by the analysis of interaction energy between cation (anion) and water molecules. Moreover, the ion pairing between choline cations and chloride anions is a dominant factor to affect the solution properties at lower water content, whereas the hydration turns to be the dominant factor with increasing water content. The competition between ion pairing and ionic hydration could be the intrinsic mechanism resulting in non-ideal properties.
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| 5. |
- Li, Jiahui, et al.
(författare)
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Extra low friction coefficient caused by the formation of a solid-like layer : A new lubrication mechanism found through molecular simulation of the lubrication of MoS2 nanoslits
- 2018
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Ingår i: Chinese Journal of Chemical Engineering. - : Elsevier. - 1004-9541 .- 2210-321X. ; 26:12, s. 2412-2419
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Tidskriftsartikel (refereegranskat)abstract
- Monolayer molybdenum disulfide (MoS2) is a novel two-dimensional material that exhibits potential application in lubrication technology. In this work, molecular dynamics was used to investigate the lubrication behaviour of different polar fluid molecules (i.e., water, methanol and decane) confined in monolayer MoS2 nanoslits. The pore width effect (i.e., 1.2, 1.6 and 2.0 nm) was also evaluated. Results revealed that decane molecules exhibited good lubricating performance compared to the other two kinds of molecules. The friction coefficient followed the order of decane < methanol < water, and decreased evidently as the slit width increased, except for decane. Analysis of the spatial distribution and mobility of different confined fluid molecules showed that a solid-like layer was formed near the slit wall. This phenomenon led to the extra low friction coefficient of confined decane molecules
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| 6. |
- Qin, Yao, et al.
(författare)
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Atomistic insight into the lubrication of glycerol aqueous solution: The role of the solid interface-induced microstructure of fluid molecules
- 2022
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Ingår i: AIChE Journal. - : John Wiley & Sons. - 0001-1541 .- 1547-5905. ; 68:4
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations are performed to investigate the solid surface-induced microstructure and friction coefficient of glycerol aqueous solutions with different water contents confined in graphene and FeO nanoslits. Results show that the friction coefficient of glycerol aqueous solutions confined in both nanoslits presents similar nonlinear variation tendencies with increasing water content, but their lowest value and the corresponding water contents differ. Distinctive microstructures of the near-surface liquid layer induced by surfaces with different hydrophilicity are responsible for their difference in lubrication. The sliding primarily occurs at the solid–liquid interface for the hydrophobic graphene nanoslit owing to almost the same velocity difference in fluid molecules. By contrast, the sliding mainly occurs at the liquid–liquid interface for the hydrophilic FeO nanoslit because of the large velocity difference in fluid molecules. The weaker the interaction force at the sliding position, the lower the friction coefficient.
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| 7. |
- Zhang, Yumeng, et al.
(författare)
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Effects of ionic hydration and hydrogen bonding on flow resistance of ionic aqueous solutions confined in molybdenum disulfide nanoslits : Insights from molecular dynamics simulations
- 2019
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Ingår i: Fluid Phase Equilibria. - : Elsevier. - 0378-3812 .- 1879-0224. ; 489, s. 23-29
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Tidskriftsartikel (refereegranskat)abstract
- Single-layer molybdenum disulfide (MoS2) is a novel two-dimensional material that has attracted considerable attention because of its excellent properties. In this work, molecular dynamics simulations were performed to investigate the effect of different kinds of alkali metal ions (Li+, Na+, and K+) on the flow resistance of ionic aqueous solutions confined in MoS2 nanoslits under shearing. Three slit widths (i.e. 1.2, 1.6, and 2.0 nm) were investigated. Simulation results showed that the friction coefficient followed the order of K+ < Na+ < Li+. The friction coefficient decreased with the increasing of slit width. Unique confined spatial distributions of different types of ionic aqueous solutions led to different confined ionic hydrations for different cations. These differences lead to different orientations of surrounding water molecules and then form different hydrogen bond (HB) networks. The friction coefficient was greatly dependent on the number of HBs per water; i.e., the larger the number of HBs formed, the lower was the flow resistance.
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| 8. |
- An, Rong, et al.
(författare)
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Atomic force microscopy probing interactions and microstructures of ionic liquids at solid surfaces
- 2022
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; :14, s. 11098-11128
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Forskningsöversikt (refereegranskat)abstract
- Ionic liquids (ILs) are room temperature molten salts that possess preeminent physicochemical properties and have shown great potential in many applications. However, the use of ILs in surface-dependent processes, e.g. energy storage, is hindered by the lack of a systematic understanding of the IL interfacial microstructure. ILs on the solid surface display rich ordering, arising from coulombic, van der Waals, solvophobic interactions, etc., all giving near-surface ILs distinct microstructures. Therefore, it is highly important to clarify the interactions of ILs with solid surfaces at the nanoscale to understand the microstructure and mechanism, providing quantitative structure–property relationships. Atomic force microscopy (AFM) opens a surface-sensitive way to probe the interaction force of ILs with solid surfaces in the layers from sub-nanometers to micrometers. Herein, this review showcases the recent progress of AFM in probing interactions and microstructures of ILs at solid interfaces, and the influence of IL characteristics, surface properties and external stimuli is thereafter discussed. Finally, a summary and perspectives are established, in which, the necessities of the quantification of IL–solid interactions at the molecular level, the development of in situ techniques closely coupled with AFM for probing IL–solid interfaces, and the combination of experiments and simulations are argued.
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| 9. |
- Gao, Qingwei, et al.
(författare)
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Effect of dimethyl carbonate on the behavior of water confined in carbon nanotube
- 2021
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Ingår i: Chinese Journal of Chemical Engineering. - : Elsevier. - 1004-9541 .- 2210-321X. ; 31, s. 177-185
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Tidskriftsartikel (refereegranskat)abstract
- The dehydration of water by dimethyl carbonate (DMC) is of great significance for its application in electrochemistry and oil industry. With the rapid development of nanomaterial, one-dimensional (e.g. carbon nanotube (CNT)) and two-dimensional (e.g. lamellar graphene) materials have been widely used for molecular sieving. In this work, the molecular behavior of dimethyl carbonate/water mixture confined in CNT with varying diameters was studied based on molecular dynamics simulation. Due to different van der Waals interactions for the components in the mixtures with the solid surface, DMC molecules are preferentially adsorbed on the inner surface of the pore wall and formed an adsorption layer. Comparing with the pure water molecules confined in CNT, the adsorption DMC layer shows notable effect on the local compositions and microstructures of water molecules under nanoconfinement, which may result in different water mobility. Our analysis shows that the surface-induced DMC molecules can destroy the hydrogen bonding network of water molecules and result in an uniform and dispersed distribution of water molecules in the tube. These clear molecular understandings can be useful in material design for membrane separation.
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| 10. |
- Gao, Qingwei, et al.
(författare)
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Molecular insight into wetting behavior of deep eutectic solvent droplets on ionic substrates : A molecular dynamics study
- 2020
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Ingår i: Journal of Molecular Liquids. - : Elsevier. - 0167-7322 .- 1873-3166. ; 319
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Tidskriftsartikel (refereegranskat)abstract
- Wetting behavior of droplets made of choline chloride/urea (1:2), an archetypal deep eutectic solvent mixture, is studied using molecular dynamics simulations. The droplets are placed on a smooth model ionic substrate with positive and negative charges of the same magnitude q (0 e ≤ q ≤ 1.0 e), corresponding to a step-by-step change from a hydrophobic to hydrophilic surface. The molecular microstructure of the droplets and their spatial compositions are systematically studied in details on how they both change while gradually moving from hydrophobic to hydrophilic surface. It is observed that urea initially forms a monolayer on the surface with a planar orientation. This layer slowly shrinks while it becomes laterally more and more constrained. It becomes also molecularly more ordered when the surface becomes hydrophilic, at the same time as the contact angles become larger and larger. The anions (Cl-) are continuously pushed further away from the charged surface. While the contact angle increases and wetting decreases, and urea forms even a secondary stable layer where it changes its orientation and turns to have one of its amines facing up and carbonyl down. The average number of urea-urea H-bonds decreases linearly while the number of ion-pair contacts increases when the urea molecules are separating from the mixture. Our analysis gives a clear molecular understanding of the process and can be useful in many applications from membrane separation to catalysis.
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| 11. |
- Gao, Qingwei, et al.
(författare)
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Physicochemical properties and structure of fluid at nano-/micro-interface : Progress in simulation and experimental study
- 2020
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Ingår i: Green Energy & Environment. - : Elsevier. - 2468-0257. ; 5:3, s. 274-285
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Forskningsöversikt (refereegranskat)abstract
- In modern chemical engineering processes, the involvement of solid/fluid interface is the most important component of process intensification techniques, such as confined membrane separation and catalysis. In the review, we summarized the research progress of the latest theoretical and experimental works to elucidate the contribution of interface to the fluid properties and structures at nano- and micro-scale. We mainly focused on water, alcohol aqueous solution, and ionic liquids, because they are classical systems in interfacial science and/or widely involved in the industrialization process. Surface-induced fluids were observed in all reviewed systems and played a critical role in physicochemical properties and structures of outside fluid. It can even be regarded as a new interface, when the adsorption layer has a strong interaction with the solid surface. Finally, we proposed a perspective on scientific challenges in the modern chemical engineering processes and outlined future prospects.
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| 12. |
- Gao, Qingwei, et al.
(författare)
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Preliminary study on mechanism of confined mass transfer and separation : "secondary confinement" effect of interfacial adsorption layer [限域传质分离机制初探:界面吸附层的"二次限域"效应]
- 2020
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Ingår i: Huagong Xuebao/CIESC Journal. - : Materials China. - 0438-1157. ; 71:10, s. 4688-4695
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Tidskriftsartikel (refereegranskat)abstract
- The confined mass transfer separation membrane is mainly for the high-precision separation process at the molecular/ion level, which is of great significance to solve the application needs of CO2 separation, azeotrope separation, lithium extraction from salt lake, desalination of seawater and so on. However, at present, the research of the confined mass transfer mechanism of this kind of membrane is lagging behind, and the theoretical models of confined mass transfer are lacking, which can no longer meet the needs of the rapid development of materials and chemical engineering. From the perspective of meso-science, the abnormal phenomenon of high flux and high selectivity of the confined mass transfer separation membrane is considered, that is, breaking through the trade-off effect, which is governed by compromise-in-competition between the selectivity mechanism and the flux mechanism. It is found that the fluid molecules will preferentially adsorb at the interface and form a stable adsorption layer. Based on this, the hypothesis of "secondary confinement" is put forward, that is, the surface induced new solid-like interface will have confinement effect on the intermediate fluid again. By comparing the pore size and the secondary confined size of the confined mass transfer separation membrane, the selective mechanism of the secondary confinement is further confirmed, and the quantitative prediction of the membrane flux and selectivity is preliminarily explored by combining the selective mechanism and the flux model, which may provide a theoretical basis for the precise construction of the limited area mass transfer membrane. © 2020, Chemical Industry Press Co., Ltd. All right reserved.
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| 13. |
- Huang, Xianzhu, et al.
(författare)
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Flow-resistance analysis of nano-confined fluids inspired from liquid nano-lubrication: A review
- 2017
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Ingår i: Chinese Journal of Chemical Engineering. - : Elsevier. - 1004-9541 .- 2210-321X. ; 25:11, s. 1552-1562
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Tidskriftsartikel (refereegranskat)abstract
- How to reduce flow resistance of nano-confined fluids to achieve a high flux is a new challenge for modern chemical engineering applications, such as membrane separation and nanofluidic devices. Traditional models are inapplicable to explain the significant differences in the flow resistance of different liquid–solid systems. On the other hand, friction reduction in liquid nano-lubrication has received considerable attention during the past decades. Both fields are exposed to a common scientific issue regarding friction reduction during liquid–solid relative motion at nanoscale. A promising approach to control the flow resistance of nano-confined fluids is to reference the factors affecting liquid nano-lubrication. In this review, two concepts of the friction coefficient derived from fluid flow and tribology were discussed to reveal their intrinsic relations. Recent progress on low or ultra-low friction coefficients in liquid nano-lubrication was summarized based on two situations. Finally, a new strategy was introduced to study the friction coefficient based on analyzing the intermolecular interactions through an atomic force microscope (AFM), which is a cutting-point to build a new model to study flow-resistance at nanoscale.
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| 14. |
- Lu, Xiaohua, et al.
(författare)
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Thermodynamic mechanism of complex fluids-solids interfacial interaction
- 2019
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Ingår i: Huagong Xuebao/CIESC Journal. - : Materials China. - 0438-1157. ; 70:10, s. 3677-3689
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Forskningsöversikt (refereegranskat)abstract
- Interfacial transfer at mesoscale is a common issue for all the multi-phase chemical processes, and the related study remains as a scientific challenge due to the complexities. Investigating the interfacial interactions at mesoscale to find out the regulation strategies is the key to realize process-intensification of mass-transfer and reaction for the advanced chemical industries. To accurately describe the behavior of fluids at the interface, a new molecular thermodynamic model that can describe the complex fluid-solid interface interaction. When the molecular thermodynamic modeling method is extended to the nano-micro interfacial transfer needs to be developed, calling for the coordination of advanced experiments at nano-micro scale and molecular with molocular thermodynamic modelling. Atomic force microscopy (AFM), which possess the sensitivity down to nanoscale, can directly obtain the interfacial interaction at nano-micro scale. The quantification of AFM-measured forces can be used to construct the coarse-grained molecular model and describe complex interfacial interaction. Then, the coarse-grained molecular model can reveal the molecular thermodynamic mechanism of nano- and micro- interface transfer, realizing quantitative prediction.
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| 15. |
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| 16. |
- Qin, Yao, et al.
(författare)
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Molecular insights into the microstructure of ethanol/water binary mixtures confined within typical 2D nanoslits : The role of the adsorbed layers induced by different solid surfaces
- 2020
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Ingår i: Fluid Phase Equilibria. - : Elsevier. - 0378-3812 .- 1879-0224. ; 509
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Tidskriftsartikel (refereegranskat)abstract
- With the emergence of membrane separation and heterogeneous catalysis applications that are associated with confined ethanol/water binary mixture in the pores of two-dimensional (2D) nanomaterials, understanding their confined microstructures is the first step for further relevant applications. In this work, molecular dynamics was performed to investigate the microstructure of ethanol/water binary mixture of 5% mole fraction confined within the four typical 2-nm width 2D-nanoslits (i.e. hBN, GO-0.2, GO-0.4 and Ti3C2(OH)2). Results demonstrated that different chemical properties of solid surfaces can induce distinctive microstructures of mixed fluid within the interfacial contact (adsorbed) layer and thus can result in different mobility of water molecules within the subcontact layer. The residence times of water molecules in the subcontact layer were found in the sequence of Ti3C2(OH)2 > hBN > GO-0.4 > GO-0.2, whereas their sequence of diffusion coefficient within the x-z plane was Ti3C2(OH)2 > hBN > GO-0.2 > GO-0.4. Detailed hydrogen bond (HB) microstructure analysis showed that a high average number of HBs (between fluid molecules of the interfacial contact layer and water molecules of the subcontact layer) induced by solid surfaces could facilitate water molecules to reside in the subcontact layer. Moreover, the small average number of HBs between the water molecules themselves in the subcontact layer could lead to high in-plane diffusion coefficients.
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| 17. |
- Zhang, Yingying, et al.
(författare)
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Energy Consumption Analysis for CO2 Separation from Gas Mixtures with Liquid Absorbents
- 2014
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 61, s. 2695-2698
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Tidskriftsartikel (refereegranskat)abstract
- CO2 separation is an energy intensive process, and it plays an important role in both energy saving and CO2 capture and storage (CCS) to deal with global-warming. CO2 can be from different sources in a wide temperature, pressure and concentrations range. Meanwhile, new liquid absorbents are under-development to cost-effectively separate CO2 from gas mixtures. All this makes it crucial to analyze the energy consumption for CO2 separation from different streams and with different absorbents. In this work, the theoretical energy consumption of CO2 separation from flue gas (CO2/N2), lime kiln gas (CO2/N2), biogas (CO2/CH4) and bio-syngas (CO2/H2/CO) was calculated. The results show that the energy consumption of CO2 separation from flue gas is the highest and that from biogas is the lowest. If the CO2 captured from flue gases was substituted by that from biogases, the energy saving would be equivalent to 28.13 million ton standard coal globally. The energy consumption of CO2 separation from biogas using traditional absorbent of 30%MEA and new developed ionic liquids (ILs) was further studied, in which 1-ethyl-3-methy- limidazolium bis[(trifluoromethyl)sulfonyl]imide ([Emim][NTf2]), 1-butyl-3-methylimida- zolium tetrafluoroborate ([Bmim][BF4]), 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide ([Hmim][Tf2N]) and 1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide ([Bmpy][Tf2N]) were screened from 75 ILs. The energy consumptions of CO2 separation using ILs are lower than those of 30%MEA and that of [Bmim][BF4] is the lowest in the four screened ILs. With a very low vapor pressure and high CO2 solubility, it's promising to use ILs as absorbents for CO2 separation.
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| 18. |
- Zhang, Yumeng, et al.
(författare)
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Molecular insight into flow resistance of choline chloride/urea confined in ionic model nanoslits
- 2021
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Ingår i: Fluid Phase Equilibria. - : Elsevier. - 0378-3812 .- 1879-0224. ; 533
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Tidskriftsartikel (refereegranskat)abstract
- Choline chloride/urea (1:2) is the most widely used deep eutectic solvent, which has attracted much attention due to its excellent advantages of low cost, environment friendly and easy synthesis. In this work, nanofriction-based molecular dynamics simulations were performed to investigate the effect of interfacial hydrophilicity on the flow resistance of Choline chloride/urea (1:2) confined in ionic model nanoslits. Simulation results showed that the flow resistance of the choline chloride/urea system increases with the increasing interfacial hydrophilicity. Urea molecules form a preferential adsorption layer on the wall. As the interfacial hydrophilicity increases, the number of urea molecules in the interfacial adsorption layer increased, whereas the stability decreased. Unique confined spatial distributions of urea molecules greatly contribute to ionic association between choline cations and chloride anions. Furthermore, with the increase of interfacial hydrophilicity, orientation distributions of urea molecules in the adsorption layer are more orderly, then causing a decrease in the average hydrogen bond number (NHB) of urea molecules. Moreover, the more the NHB of urea molecules, the better is the stability in the interfacial adsorption layer, which in turn results in less flow resistance.
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| 19. |
- Zhang, Yumeng, et al.
(författare)
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Progress in molecular-simulation-based research on the effects of interface-induced fluid microstructures on flow resistance
- 2019
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Ingår i: Chinese Journal of Chemical Engineering. - : Elsevier. - 1004-9541 .- 2210-321X. ; 27:6, s. 1403-1415
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Tidskriftsartikel (refereegranskat)abstract
- In modern chemical engineering processes, solid interface involvement is the most important component of process intensification techniques, such as nanoporous membrane separation and heterogeneous catalysis. The fundamental mechanism underlying interfacial transport remains incompletely understood given the complexity of heterogeneous interfacial molecular interactions and the high nonideality of the fluid involved. Thus, understanding the effects of interface-induced fluid microstructures on flow resistance is the first step in further understanding interfacial transport. Molecular simulation has become an indispensable method for the investigation of fluid microstructure and flow resistance. Here, we reviewed the recent research progress of our group and the latest relevant works to elucidate the contribution of interface-induced fluid microstructures to flow resistance. We specifically focused on water, ionic aqueous solutions, and alcohol–water mixtures given the ubiquity of these fluid systems in modern chemical engineering processes. We discussed the effects of the interface-induced hydrogen bond networks of water molecules, the ionic hydration of ionic aqueous solutions, and the spatial distributions of alcohol and alcohol–water mixtures on flow resistance on the basis of the distinctive characteristics of different fluid systems.
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| 20. |
- Zhao, Nana, et al.
(författare)
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Atomistic insights into the effects of carbonyl oxygens in functionalized graphene nanopores on Ca2+/Na+ sieving
- 2020
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 164, s. 305-316
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Tidskriftsartikel (refereegranskat)abstract
- Residual Ca2+ decreases the efficiency and increases the power consumption of the chlor-alkali industry. However, Ca2+ and Na+ sieving is challenging due to the similar ionic radii of these cations. Inspired by the presence of carbonyl oxygens in key selective filters of biological Ca2+ and Na+ channels, we used molecular dynamics to investigate the effects of carbonyl oxygen atoms in modified graphene nanopores of various sizes (characteristic diameters: 0.57–1.50 nm) on Ca2+/Na+ sieving. The results demonstrated that selectivity is closely associated with the different roles of the carbonyl oxygen atoms. In small nanopores, Ca2+ sheds increased numbers of water molecules due to the predominant steric effect of carbonyl oxygen atoms. Thus, Ca2+ must overcome a higher energy barrier than Na+. This requirement prevents the passage of Ca2+. In large nanopores, carbonyl oxygen atoms do preferentially substitute water molecules outside the first hydration shell of Ca2+ compared with those outside the first hydration shell of Na+, thereby hindering Na+ departure from the nanopore. These findings provide useful guidance for the further development of Ca2+ separation materials as sensors and ion separators.
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| 21. |
- Zhu, Yudan, et al.
(författare)
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Lubrication Behavior of Water Molecules Confined in TiO2 Nanoslits : A Molecular Dynamics Study
- 2016
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Ingår i: Journal of Chemical and Engineering Data. - : American Chemical Society (ACS). - 0021-9568 .- 1520-5134. ; 61:12, s. 4023-4030
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Tidskriftsartikel (refereegranskat)abstract
- Titanium (Ti) metal has been widely used in orthopedic implants, such as knee replacements and fracture fixation devices, where water is the base fluid of the lubricant. In this work, a series of nonequilibrium molecular dynamics have been carried out to investigate the microstructure and lubrication of water molecules confined in TiO2 nanoslits under shearing. The effects of varying slit gap widths (0.8, 1.2, 1.6, and 2.0 nm) and shear velocities (200, 100, 50, and 10 m/s) on the friction coefficients between TiO2 and water molecules were evaluated to shed light on the role of the confined water molecules on lubrication. Simulation results showed that the friction coefficient decreased as the slit width increased. Detailed analysis of water molecules microstructure revealed that water molecules confined in the slits were layered. Typically, all the water molecules in Layer 1 and some water molecules in Layer 2 could reach the sliding velocity of the wall, which were in agreement with the reported mobility of water molecules absorbed on TiO2 nanoparticles via nuclear magnetic resonance. As the width of slit gap increased, the average lifetime of the H-bonds between water molecules within and beyond Layer 1 reduced and the amount of free water increased accordingly, which caused a decrease in the friction coefficient. This understanding can be used to explain at the molecular scale the observation in our previous atomic force microscope experiment in which the higher roughness in TiO2 reflected a lower friction coefficient.
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