| 1. |
- An, Rong, et al.
(author)
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Ionic liquids on uncharged and charged surfaces: In situ microstructures and nanofriction
- 2022
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In: Friction. - : Springer. - 2223-7690 .- 2223-7704. ; 10:11, s. 1893-1912
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Journal article (peer-reviewed)abstract
- In situ changes in the nanofriction and microstructures of ionic liquids (ILs) on uncharged and charged surfaces have been investigated using colloid probe atomic force microscopy (AFM) and molecular dynamic (MD) simulations. Two representative ILs, [BMIM][BF4] (BB) and [BMIM][PF6] (BP), containing a common cation, were selected for this study. The torsional resonance frequency was captured simultaneously when the nanoscale friction force was measured at a specified normal load; and it was regarded as a measure of the contact stiffness, reflecting in situ changes in the IL microstructures. A higher nanoscale friction force was observed on uncharged mica and highly oriented pyrolytic graphite (HOPG) surfaces when the normal load increased; additionally, a higher torsional resonance frequency was detected, revealing a higher contact stiffness and a more ordered IL layer. The nanofriction of ILs increased at charged HOPG surfaces as the bias voltage varied from 0 to 8 V or from 0 to —8 V. The simultaneously recorded torsional resonance frequency in the ILs increased with the positive or negative bias voltage, implying a stiffer IL layer and possibly more ordered ILs under these conditions. MD simulation reveals that the [BMIM]+ imidazolium ring lies parallel to the uncharged surfaces preferentially, resulting in a compact and ordered IL layer. This parallel “sleeping” structure is more pronounced with the surface charging of either sign, indicating more ordered ILs, thereby substantiating the AFM-detected stiffer IL layering on the charged surfaces. Our in situ observations of the changes in nanofriction and microstructures near the uncharged and charged surfaces may facilitate the development of IL-based applications, such as lubrication and electrochemical energy storage devices, including supercapacitors and batteries.
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| 2. |
- Dai, Zhongyang, et al.
(author)
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Unique Structures and Vibrational Spectra of Protic Ionic Liquids Confined in TiO2 Slits: The Role of Interfacial Hydrogen Bonds
- 2018
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 34:44, s. 13449-13458
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Journal article (peer-reviewed)abstract
- The ionic liquid (IL)/titanium dioxide (TiO2) interface exists in many application systems, such as nanomaterial synthesis, catalysis, and electrochemistry systems. The nanoscale interfacial properties in the above systems are a common issue. However, directly detecting the interfacial properties of nanoconfined ILs by experimental methods is still challenging. To help better learn about the interfacial issue, molecular dynamics simulations have been performed to explore the structures, vibration spectra, and hydrogen bond (HB) properties at the IL/TiO2 interface. Ethylammonium nitrate (EAN) ILs confined in TiO2 slit pores with different pore widths were studied. A unique vibrational spectrum appeared for EAN ILs confined in a 0.7 nm TiO2 slit, and this phenomenon is related to interfacial hydrogen bonds (HBs). An analysis of the HB types indicated that the interfacial NH3+ group of the cations was in an asymmetric HB environment in the 0.7 nm TiO2 slit, which led to the disappearance of the symmetric N–H stretching mode. In addition, the significant increase in the HB strength between NH3+ groups and the TiO2 surface slowed down the stretching vibration of the N–H bond, resulting in one peak in the vibrational spectra at a lower frequency. For the first time, our simulation work establishes a molecular-level relationship between the vibrational spectrum and the local HB environment of nanoconfined ILs at the IL/TiO2 interface, and this relationship is helpful for interface design in related systems.
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| 3. |
- Dai, Zhongyang, et al.
(author)
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Wetting control through topography and surface hydrophilic/hydrophobic property changes by coarse grained simulation
- 2017
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In: Molecular Simulation. - : Taylor & Francis. - 0892-7022 .- 1029-0435. ; 43:13-16, s. 1202-1208
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Journal article (peer-reviewed)abstract
- The changes of wetting state of water droplet on the solid surface featuring pillared structures are quantitatively studied by Coarse Grained simulation. Our results demonstrate that wetting state changes with the different topography (surface roughness), and it depends on the intrinsic hydrophilic/hydrophobic property of surface as well. Only if the contact angle of water droplet on the smooth surface is larger than 93.13°, the wetting state translates from the Wenzel state to the Cassie state on the rough surface with certain pillar height and width, and the contact angle climb up to the highest point and then remain almost unchanged with the increasing of pillar height and the same pillar distance. However, the wetting state does not change if the contact angle on the smooth surface is 85.1° or less, no matter what pillar structure the surface has. Additionally, the contact angles will remain almost unchanged if the pillar height is higher than a certain value. Our simulation results provide a quantitative understanding about the wetting state of water droplet on solid rough surfaces, and the results show the wetting state can be controlled by combining rough structure design and hydrophilic/hydrophobic property change of surfaces.
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| 4. |
- Lu, Xiaohua, et al.
(author)
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Nano-interface enhanced CO2 absorption and mechanism analysis
- 2020
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In: Huagong Xuebao/CIESC Journal. - : Materials China. - 0438-1157. ; 71:1, s. 34-42
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Journal article (peer-reviewed)abstract
- CO2 capture and separation (CCS) is a key step to mitigate greenhouse gas emissions and develop renewable energy. The trade-off between the rate and efficiency in the CO2 separation process cannot be solved with the traditional process intensification. Using nano-interface to realize process intensification has been widely used in the chemical process with multi-phase transfer, and CO2 separation is one of examples. This review summarizes the research work from the establishment of CO2 transfer model at nano-interface and the resistance regulation, the acquisition of the CO2 chemical potentials at equilibrium and at the nano-interface (the driving force regulation) and the molecular simulation analysis of the interface enhancement mechanism. Based on the theoretical studies, the resistance distribution for the CO2 separation process in a real absorption tower is further analyzed and a "three-stage strengthening scheme" is proposed to decrease the investment and operating costs. © All Right Reserved.
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| 5. |
- Lu, Xiaohua, et al.
(author)
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Thermodynamic mechanism of complex fluids-solids interfacial interaction
- 2019
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In: Huagong Xuebao/CIESC Journal. - : Materials China. - 0438-1157. ; 70:10, s. 3677-3689
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Research review (peer-reviewed)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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| 6. |
- Qin, Yao, et al.
(author)
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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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In: Fluid Phase Equilibria. - : Elsevier. - 0378-3812 .- 1879-0224. ; 509
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Journal article (peer-reviewed)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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| 7. |
- Wang, Tiantian, et al.
(author)
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Microstructural probing of phosphonium-based ionic liquids on a gold electrode using colloid probe AFM
- 2022
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 24:41, s. 25411-25419
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Journal article (peer-reviewed)abstract
- Atomic force microscopy (AFM) with a gold colloid probe modeled as the electrode surface is employed to directly capture the contact resonance frequency of two phosphonium-based ionic liquids (ILs) containing a common anion [BScB]− and differently lengthened cations ([P6,6,6,14]+ and [P4,4,4,8]+). The comparative interfacial studies are performed by creating IL films on the surface of gold, followed by measuring the wettability, thickness of the films, adhesion forces, surface morphology and AFM-probed contact resonance frequency. In addition, the cyclic voltammetry and impedance spectroscopy measurements of the neat ILs are measured on the surface of the gold electrode. The IL with longer cation alkyl chains exhibits a well-defined thin film on the electrode surface and enhanced the capacitance than the shorter chain IL. The AFM contact resonance frequency and force curves reveal that the longer IL prefers to form stiffer ion layers at the gold electrode surface, suggesting the “…anion–anion–cation–cation…” bilayer structure, in contrast, the shorter-chain IL forms the softer cation–anion alternating structure, i.e., “…anion–cation–anion–cation…”.
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| 8. |
- Wei, Yudi, et al.
(author)
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Molecular interactions of ionic liquids with SiO2 surfaces determined from colloid probe atomic force microscopy
- 2022
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 24:21, s. 12808-12815
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Journal article (peer-reviewed)abstract
- Ionic liquids (ILs) interact strongly with many different types of solid surfaces in a wide range of applications, e.g. lubrication, energy storage and conversion, etc. However, due to the nearly immeasurable large number of potential ILs available, identifying the appropriate ILs for specific solid interfaces with desirable properties is a challenge. Theoretical studies are highly useful for effective development of design and applications of these complex molecular systems. However, obtaining reliable force field models and interaction parameters is highly demanding. In this work, we apply a new methodology by deriving the interaction parameters directly from the experimental data, determined by colloid probe atomic force microscopy (CP-AFM). The reliability of the derived interaction parameters is tested by performing molecular dynamics simulations to calculate translational self-diffusion coefficients and comparing them with those obtained from NMR diffusometry.
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