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• Zhang, Bencan; Qu, Yongxiao; Luo, Gaoyang; Fu, Yuequn; Zhang, Zhisen & Wu, Jianyang (2026). Competing Dipole Ordering and Hydrogen-Bond Reorganization Regulate Hydrogen-Tetrahydrofuran Clathrate Growth at the Hydrate–Liquid Interface. Langmuir. ISSN 0743-7463. 42(36), p. 26803–26815. doi: 10.1021/acs.langmuir.6c03903. Full text in Research Archive
• Chang, Yuanhao; Xiao, Senbo; Fu, Yuequn; Li, Hanzhou; Li, Xiang & Ma, Rui [Show all 7 contributors for this article] (2026). Transport and rupture dynamics of the Pickering emulsion in oil-filled nanopore throats. Journal of Molecular Liquids. ISSN 0167-7322. 441, p. 129036–129036. doi: 10.1016/j.molliq.2025.129036. Full text in Research Archive
• Fu, Yuequn & Flekkøy, Eirik Grude (2025). Molecular simulations of cavitation bubble dynamics. Frontiers in Physics. 13. doi: 10.3389/fphy.2025.1614785. Full text in Research Archive Show summary

  We study the cavitation bubble that forms as a nano-scale spherical surface is detached from a flat surface using molecular dynamics (MD) simulations. This investigation maps the onset and early development stages of cavitation at the nanoscale. We study the effects of variable pulling speeds and ambient pressures on the dynamics of the vapor bubble. It was observed that a higher pulling speed increases the cavitation volume but reduces the bubble’s lifetime. On the other hand, ambient pressure variations significantly influence both the maximum volume and the collapse rate of the cavitation. The results are summarized in a phase diagram that displays the effects of these varying pulling speeds and ambient pressures. Significantly, the study corroborates a Family-Vicsek scaling law for the bubble volume evolution.

• Liu, Xintong; Zhang, Yu; Shi, Qiao; Qu, Yongxiao; Hao, Yongchao & Fu, Yuequn [Show all 8 contributors for this article] (2025). Machine-learning insights into the mechanical strength of methane hydrate-silica interfaces. Journal of Physics D: Applied Physics. ISSN 0022-3727. 58(13). doi: 10.1088/1361-6463/adb0d2. Full text in Research Archive
• Lin, Yanwen; Yan, Weiwei; Zhang, Yi; Wang, Ping; Shi, Qiao & Hao, Yongchao [Show all 12 contributors for this article] (2024). Effects of shear loading rate on tetrahydrofuran Hydrate Adhesion strength for enhanced flow assurance. Engineering Fracture Mechanics. ISSN 0013-7944. 298. doi: 10.1016/j.engfracmech.2024.109946. Full text in Research Archive
• Liu, Siqi; Wan, Di; Guan, Shuai; Fu, Yuequn; Zhang, Zhiliang & He, Jianying (2024). A comparative study on nanoscale mechanical properties of CrMnFeCoNi high-entropy alloys fabricated by casting and additive manufacturing. Journal of Materials Research and Technology (JMR&T). ISSN 2238-7854. 33, p. 1211–1219. doi: 10.1016/j.jmrt.2024.09.146. Full text in Research Archive Show summary

  Additive manufacturing (AM) has emerged as a pioneering method for fabricating high entropy alloys (HEAs), yet a comprehensive comparison of their nanoscale mechanical properties with those produced by the conventional casting method remains unexplored. In this study, the nanoindentation was utilized to investigate the nanoscale elastic and plastic characteristics in both additive-manufactured (AM-ed) and as-casted single-phase face-centered cubic (FCC) equiatomic CrMnFeCoNi HEAs. Herein, the hardness, reduced modulus, indentation size effect (ISE), yield strength, fracture toughness, and strain rate sensitivity were comprehensively investigated. The results indicated that the hardness of AM-ed HEA was higher than the as-casted HEA, and the reduced modulus values showed no notable distinction between the two samples. The AM-ed HEA demonstrated simultaneous enhancements in yield strength and fracture toughness compared to the as-casted HEA. The as-casted HEA possessed a more distinct indentation size effect (ISE) than the AM-ed HEA. It was observed that the AM-ed HEA exhibited relatively lower strain rate sensitivity and a larger activation volume. This direct comparison of the mechanical properties and deformation mechanisms from a nanoscale view offers unique insights for optimizing and advancing AM techniques in the fabrication of HEAs.

• Lin, Yanwen; Zhou, Ziyue; Song, Zixuan; Shi, Qiao; Hao, Yongchao & Fu, Yuequn [Show all 9 contributors for this article] (2024). Insights into the mechanical stability of tetrahydrofuran hydrates from experimental, machine learning, and molecular dynamics perspectives. Nanoscale. ISSN 2040-3364. p. 6296–6308. doi: 10.1039/d3nr04940j. Full text in Research Archive Show summary

  Natural gas hydrates (NGHs) hold immense potential as a future energy resource and for sustainable applications such as gas capture and storage. Due to the challenging formation conditions, however, their mechanical properties remain poorly understood. Herein, the mechanical characteristics of tetrahydrofuran (THF) hydrates, a proxy for methane hydrates, were investigated at different ice contents, strain rates, and temperatures using uniaxial compressive experiments. The results unveil a distinct behavior in the peak strength of THF hydrates with a varying ice content, strain rate and temperature, exhibiting an increase as the strain rate and temperature decrease, in contrast to the peak strength–strain rate relationship observed in polycrystalline ice. Based on the experimental data, four machine learning (ML) models including extreme gradient boosting (XGboost), multilayer perceptron (MLP), gradient boosting decision tree (GBDT) and decision tree (DT) were developed to predict the peak strength. The XGboost model demonstrates superior predictive performance, emphasizing the significant influence of ice content and temperature on the peak strength of hydrates. Furthermore, molecular dynamics (MD) simulations were employed to gain insights into the dissociation and formation processes of clathrate cages, as well as phase transitions and amorphization occurring at grain boundaries (GBs) involving diverse unconventional clathrate cages, including 51265, 4151062, 4151064, 425861 and 425862, with 425861 and 425862 cages being predominant. This study enhances our understanding of the mechanical properties and deformation mechanisms of hydrates and provides a ML-based predictive framework for estimating the compressive strength of hydrates under diverse coupling conditions. The findings have significant implications for stability assessments of NGHs and the exploitation of NGH resources.

• Zhang, Yu; Liu, Xintong; Shi, Qiao; Qu, Yongxiao; Hao, Yongchao & Fu, Yuequn [Show all 8 contributors for this article] (2024). Mechanical properties and cage transformations in CO2-CH4 heterohydrates: a molecular dynamics and machine learning study. Journal of Physics D: Applied Physics. ISSN 0022-3727. 57(46). doi: 10.1088/1361-6463/ad6dcf. Full text in Research Archive
• Yang, Yuqi; Xu, Zhengchao; Chen, Siyu; Zhang, Haipeng; Fu, Yuequn & Liu, Siqi [Show all 8 contributors for this article] (2024). Study on the secondary flow in T-shaped pipe with different outlet surfaces. Physics of Fluids. ISSN 1070-6631. 36(10). doi: 10.1063/5.0229019. Full text in Research Archive
• Lin, Yanwen; Hao, Yongchao; Shi, Qiao; Xu, Yihua; Song, Zixuan & Zhou, Ziyue [Show all 9 contributors for this article] (2023). Enhanced formation of methane hydrates via graphene oxide: Machine learning insights from molecular dynamics simulations. Energy. ISSN 0360-5442. 289. doi: 10.1016/j.energy.2023.130080. Full text in Research Archive
• Zeng, Jincheng; Zhou, Ziyue; Song, Zixuan; Lu, Hao; Liu, Yisi & Qiao, Shi [Show all 9 contributors for this article] (2023). Electric field as a crystallization switch of heterogeneous ice formation. Journal of Physics: Condensed Matter. ISSN 0953-8984. 35(44). doi: 10.1088/1361-648X/ace5ff. Full text in Research Archive
• Wang, Feng; Xiao, Senbo; Luo, Sihai; Fu, Yuequn; Skallerud, Bjørn Helge & Kristiansen, Helge [Show all 12 contributors for this article] (2023). Surface wrinkling with memory for programming adhesion and wettability. ACS Applied Nano Materials. 6, p. 4097–4104. doi: 10.1021/acsanm.2c05410. Full text in Research Archive Show summary

  Modulating surface wrinkling is important for a variety of engineering applications. It has been known for more than two decades that the wavelength of surface wrinkles occurring in a metal film–soft polymer system scales linearly with the deposited film thickness. In the current experimental study of ultrathin gold film (0.2–8 nm) deposition on polydimethylsiloxane (PDMS), an unexplored thickness-dependent wrinkling phenomenon is found. By manipulating the deposition sequence as a degree of freedom for tailoring surface topography, we discovered a morphology memory effect where the wrinkle evolution in the subsequent deposition step inherits the surface pattern already formed in the previous step. Moreover, a stepwise deposition targeting 1 nm thick film can lead to 1 order of magnitude higher surface roughness than the one in the continuous deposition. By programming the sequences within 8 nm Au deposition, a surface strain map varying drastically from 0.2% to 27% is realized. Instructed by the strain map, we show the great potentials of tailored wrinkles in alternating surface wettability, enhancing surface Raman scattering, and on-demand tuning of surface adhesion.

• Wang, Feng; Fu, Yuequn; Xiao, Senbo; Skallerud, Bjørn Helge; Liu, Siqi & Luo, Sihai [Show all 9 contributors for this article] (2023). Thickness Mediated Morphology Evolution in Sub-10-nm Metal Film Deposition: Implications for Nondestructive Testing. ACS Applied Nano Materials. doi: 10.1021/acsanm.3c01533. Full text in Research Archive Show summary

  Thickness in sub-10-nm metal film deposition is a seldomly explored parameter that can influence not only the film mechanical properties but also the surface functional characteristics. In this study, we designed bilayer systems comprising Au on a polydimethylsiloxane (PDMS) substrate to reveal a unique thickness-mediated surface morphology evaluation phenomenon. Our results show that, within a specific range of elastic modulus of the selected PDMS substrate, surface wrinkling starts when the deposited theoretical Au thickness is around 0.2 nm, reaches a maximum deformation at thickness 1 ~ 2 nm, and disappears when the thickness is equal or larger than 8 nm. The thickness-mediated wrinkling on and off suggests that film thickness can strongly impact the patterns observed on soft elastomers. This finding indicates that what we observed may not be the intrinsic surface properties but rather a thickness-controlled wrinkling. Using 2 nm Au deposition as a highly sensitive non-destructive testing method, a potential application for identifying surface defects on solid surfaces is proposed.

• Song, Zixuan; Zhou, Ziyue; Lin, Yanwen; Shi, Qiao; Hao, Yongchao & Fu, Yuequn [Show all 8 contributors for this article] (2023). Hydrogen diffusion in C 1 ′ phase clathrate hydrate. Chinese Physics B. ISSN 1674-1056. 32(6). doi: 10.1088/1674-1056/accd4b. Full text in Research Archive
• Lin, Yanwen; Shi, Qiao; Hao, Yongchao; Song, Zixuan; Zhou, Ziyue & Fu, Yuequn [Show all 9 contributors for this article] (2023). The effect of non-uniform pitch length and spiraling pathway on the mechanical properties of coiled carbon nanotubes. International Journal of Mechanical Sciences. ISSN 0020-7403. 257. doi: 10.1016/j.ijmecsci.2023.108532. Full text in Research Archive Show summary

  Coiled carbon nanotubes (CCNTs) exhibit exceptional mechanical, electrical, and thermal properties, making them suitable for diverse applications such as nanoelectromechanical devices. Here, classic molecular dynamics (MD) simulations were employed to investigate the coil morphology and the uniaxial tensile characteristics of thirteen CCNTs that were constructed by twisting carbon nanotube (CNT) segments of toroid formed by six identical CNT segments, with intricate effects of coil spacing and twist-induced spiraling pathway. The MD results showed that the coil morphology and stretching properties of CCNTs are greatly dictated by pitch length and spiraling pathway. All CCNTs showed unique characteristics of sawtooth-like patterns in the tensile stress-strain curves, originating from the separation of van der Waals (vdW) attracted coils, strain-induced buckling of CNT segments and nanohinge-like plastic deformations. Depending on the non-uniform pitch length and spiraling pathway of twisted CCNT segments, CCNTs exhibit different mechanical properties including Young's modulus, elastic limit, tensile strength, fracture strain, stiffness coefficient and distinguishing deformation mechanisms. Particularly, the fracture strain and tensile strength are significantly dictated by the pitch length and spiraling pathway, respectively. The elastic proprieties of finite element (FE) models scaled to CCNTs were established for comparison with the case of CCNTs with symmetrical spiraling. Moreover, CCNTs show high toughness that can be controlled by the pitch length and spiraling pathway. This study provides new insights and perspectives into the mechanical properties of nanocoils, which is of help to designing optimal nanocoils for nano-device systems.

• Zhang, Yu; Song, Zixuan; Lin, Yanwen; Shi, Qiao; Hao, Yongchao & Fu, Yuequn [Show all 8 contributors for this article] (2023). Predicting mechanical properties of CO2 hydrates: machine learning insights from molecular dynamics simulations. Journal of Physics: Condensed Matter. ISSN 0953-8984. 36(1). doi: 10.1088/1361-648X/acfa55. Full text in Research Archive Show summary

  Understanding the mechanical properties of CO2 hydrate is crucial for its diverse sustainable applications such as CO2 geostorage and natural gas hydrate mining. In this work, classic molecular dynamics (MD) simulations are employed to explore the mechanical characteristics of CO2 hydrate with varying occupancy rates and occupancy distributions of guest molecules. It is revealed that the mechanical properties, including maximum stress, critical strain, and Young's modulus, are not only affected by the cage occupancy rate in both large 51262 and small 512 cages, but also by the distribution of guest molecules within the cages. Specifically, the presence of vacancies in the 51262 large cages significantly impacts the overall mechanical stability compared to 512 small cages. Furthermore, four distinct machine learning (ML) models trained using MD results are developed to predict the mechanical properties of CO2 hydrate with different cage occupancy rates and cage occupancy distributions. Through analyzing ML results, as-developed ML models highlight the importance of the distribution of guest molecules within the cages, as crucial contributor to the overall mechanical stability of CO2 hydrate. This study contributes new knowledge to the field by providing insights into the mechanical properties of CO2 hydrates and their dependence on cage occupancy rates and cage occupancy distributions. The findings have implications for the sustainable applications of CO2 hydrate, and as-developed ML models offer a practical framework for predicting the mechanical properties of CO2 hydrate in different scenarios.

• Zhou, Ziyue; Zeng, Jincheng; Song, Zixuan; Lin, Yanwen; Shi, Qiao & Hao, Yongchao [Show all 9 contributors for this article] (2023). Thermal conductivity of fivefold twinned silicon-germanium heteronanowires. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. doi: 10.1039/d3cp02926c. Full text in Research Archive Show summary

  The thermal transport properties of five-fold twinned (5FT) germanium–silicon (Ge–Si) heteronanowires (h-NWs) with varying cross-sectional areas, germanium (Ge) domain ratios and heterostructural patterns are investigated using homogeneous nonequilibrium molecular dynamics (HNEMD) simulations. The results demonstrate a distinctive behavior in the thermal conductivity (κ) of 5FT-NWs, characterized by a “flipped” trend at a critical cross-sectional area. This behavior is attributed to the hydrodynamic phonon flow, arising from the normal three-phonon scattering process in the low-frequency region. In addition, the composition ratio of 5FT-NWs has a significant impact on reducing the κ of 5FT-NWs and suppressing the hydrodynamic effect. Intriguingly, as the homogeneous element domains are separated, stronger phonon hydrodynamic flows are observed in comparison to the adjacent homogeneous element domains. By analyzing various phonon properties, including phonon dispersion, three-phonon scattering rate, and phonon mean free path, critical insights into the origin of the differential κ in different 5FT-NW structures are provided. The findings deepen the understanding of the thermal transport properties of nanomaterials and hold implications for the design and development of nanoelectronics and thermoelectric devices.

• Shi, Qiao; Lin, Yanwen; Hao, Yongchao; Song, Zixuan; Zhou, Ziyue & Fu, Yuequn [Show all 8 contributors for this article] (2023). Unconventional growth of methane hydrates: A molecular dynamics and machine learning study. Energy. ISSN 0360-5442. 282. doi: 10.1016/j.energy.2023.128337. Full text in Research Archive Show summary

  Natural gas hydrate reservoirs in natural settings subjected to external driving forces are deformed and locally dissociated, while they reform due to endothermic dissociation reaction. Here we report a molecular dynamics (MD) and machine learning (ML) study of unconventional growth characteristics of methane hydrates (MH). MD results show that depending on the strain of MH substrate, methane clathrate hydrates grow via four distinct growth modes, in which diverse unconventional cages are critically involved. Interestingly, a novel new MH structure named as MH-VII composed of 51263, 51472 and 425861 polyhedral cages is discovered. Moreover, a long short-term memory (LSTM) neural network-based ML model using short-time MD information is developed to effectively predict the complex dynamic growth of MH in terms of clathrate cages and F4 order parameter. This work provides new insights and perspectives into the growth of clathrate hydrates, and as-developed LSTM-based ML model opens a critical pathway for exploring time-dependent behaviors of clathrate hydrates under complex conditions.

• Fu, Yuequn; Xiao, Senbo; Liu, Siqi; Chang, Yuanhao; Ma, Rui & Zhang, Zhiliang [Show all 7 contributors for this article] (2022). Atomistic Insights into the Droplet Size Evolution during Self-Microemulsification. Langmuir. ISSN 0743-7463. 38(10), p. 3129–3138. doi: 10.1021/acs.langmuir.1c03099. Full text in Research Archive Show summary

  Microemulsions have been attracting great attention for their importance in various fields including nanomaterials fabrication, food industry, drug delivery, and enhanced oil recovery. Atomistic insights into the self-microemulsifying process and the underlying mechanisms are crucial for the design and tuning of the size of microemulsion droplets towards applications. In this work, coarse-grained models were used to investigate the role of droplet sizes played in the preliminary self-microemulsifying process. Time evolution of liquid mixtures consisting of several hundreds of water/surfactant/oil droplets was resolved in large-scale simulations. By monitoring the size variation of the microemulsion droplets in the self-microemulsifying process, the dynamics of diameter distribution of water/surfactant/oil droplets were studied. The underlying mass transport mechanisms responsible for droplet size evolution and stability were elucidated. Specifically, temperature effects on the droplet size were clarified. This work supplies the knowledge of the self-microemulsifying of the water-in-oil microemulsions at the nanoscale. The results are expected to serve as guidelines for practical strategies for preparing a microemulsion system with desirable droplet sizes and properties.

• Liu, Siqi; Wan, Di; Peng, Ding; Lu, Xu; Ren, Xiaobo & Fu, Yuequn [Show all 10 contributors for this article] (2022). Effect of heat input on nanomechanical properties of wire-arc additive manufactured Al 4047 alloys. Materials Science & Engineering: A. ISSN 0921-5093. 860. doi: 10.1016/j.msea.2022.144288. Full text in Research Archive Show summary

  Heat input is one of the most important process parameters during additive manufacturing (AM). It is of great significance to understand the effect of heat input on the microstructure and nanomechanical properties, as well as the underlying mechanisms. Wire-arc additive manufactured (WAAM-ed) Al 4047 alloys under different heat inputs were produced and studied in this work. The as-manufactured Al alloys showed hypoeutectic microstructure that consisted of primary Al (α-Al) dendrite and ultrafine Al–Si eutectic. The effect of heat input on hardness and strain rate sensitivity (SRS) were investigated through nanoindentation. The nanohardness decreased with the increasing heat input, in accordance with the trend of yield strength and microhardness in the previous studies, in which the mechanism was usually explained by the grain growth model and Hall-Petch relationship. This work suggests a distinct mechanism regarding the effect of heat input on nanohardness, which is the enhanced solid solution strengthening produced by lower heat input. In addition, the heat input had little effect on the SRS and activation volume. It is hoped that this study leads to new insights into the understanding of the relation between heat input and nanomechanical properties, and further benefits to improve the targeted mechanical properties and engineering applications of the AM-ed materials.

• Zhou, Ziyue; Xu, Ke; Song, Zixuan; Wang, Zhen; Lin, Yanwen & Shi, Qiao [Show all 10 contributors for this article] (2022). Isotope doping-induced crossover shift in the thermal conductivity of thin silicon nanowires. Journal of Physics: Condensed Matter. ISSN 0953-8984. 35. doi: 10.1088/1361-648X/acab4a. Full text in Research Archive
• Xu, Ke; Lin, Yanwen; Li, Tong; Fu, Yuequn; Zhang, Zhisen & Wu, Jianyang (2022). Structural and mechanical stability of clathrate hydrates encapsulating monoatomic guest species. Journal of Molecular Liquids. ISSN 0167-7322. 347. doi: 10.1016/j.molliq.2021.118391. Full text in Research Archive
• Liu, Siqi; Chang, Zexin; Fu, Yuequn; liu, yuyu; Lin, Meichao & Ren, Xiaobo [Show all 9 contributors for this article] (2022). Nanoscale creep behavior and its size dependency of a Zr-based bulk metallic glass manufactured by selective laser melting. Materials & design. ISSN 0264-1275. 218. doi: 10.1016/j.matdes.2022.110723. Full text in Research Archive Show summary

  Nanoscale creep behaviors of metallic glasses (MGs) have gathered considerable interests in recent years, owing to their distinct atomistic mechanisms of plasticity. Additive manufacturing (AM) is a burgeoning technique for manufacturing MGs, the nanoscale creep characteristics and creep mechanism of the AM-ed MGs, however, remain ambiguous. In this work, the nanoscale creep behavior and creep size effect of a selective laser melted (SLM-ed) Zr-based MG were investigated by using nanoindentation. In an effort to gain more insight into the creep behaviors, the creep compliance and creep retardation spectra were extracted. The creep stress exponent (n) and shear transformation zone (STZ) volume, as the indicators of the creep mechanism, were estimated. The values of n are in the range of 2-3, and STZ volumes are around 2 nm3. The creep resistance of the MG was found to decrease with the increasing applied peak loads. A potential mechanism for this creep size effect was revealed: the smaller of the STZ volume, as well as the greater ratio of plastic flow under the higher maximum load, are responsible for the decreasing tendency of creep resistance. This research gives a comprehensive understanding of the atomistic mechanisms in the AM-ed MG during the nanoscale creep deformation process and can serve as a reference for improving the plasticity and further engineering applications.

• Fu, Yuequn; Xiao, Senbo; Skallerud, Bjørn Helge; Zhang, Zhiliang & He, Jianying (2022). Assembly graphene platelets for bioinspired, stimuli-responsive, low ice adhesion surfaces. ACS Omega. 7, p. 10225–10234. doi: 10.1021/acsomega.1c06782. Full text in Research Archive Show summary

  Design and fabrication of functional materials for anti-icing and de-icing attract great attention from both academic research and industry. Among them, the study of fish-scale-like material has been proved that enabling sequential rupture is an effective approach for weakening the intrinsic interface adhesion. Here, graphene platelets were utilized to construct fish-scale-like surfaces for easy ice detachment. Using a biomimicking arrangement of the graphene platelets, the surfaces were able to alter their structural morphology for sequential rupture in response to external forces. With different packing densities of graphene platelets, all the surfaces showed universally at least 50% of reduction in atomistic tensile ice adhesion strength. Because of the effect of sequential rupture, stronger ice-surface interactions did not lead to an obvious increase in ice adhesion. Interestingly, the high packing density of graphene platelets resulted in stable and reversible surface morphology in cyclic tensile and shearing tests, and subsequently high reproducibility of sequential rupture mode. The fish-scale-like surfaces built and tested, together with the nanoscale de-icing results, provided a close view of ice adhesion mechanics, which can promote future bio-inspired stress-responsive anti-icing surface designs.

• Wang, Peng; Wang, Jun; Xu, Ke; Lin, Yanwen; Shi, Qiao & Li, Tong [Show all 9 contributors for this article] (2022). Mechanical stability of fluorinated-methane clathrate hydrates. Journal of Molecular Liquids. ISSN 0167-7322. 360. doi: 10.1016/j.molliq.2022.119553. Full text in Research Archive
• Ma, Rui; Xiao, Senbo; Chang, Yuanhao; Fu, Yuequn; He, Jianying & Zhang, Zhiliang (2022). An interfacial gas-enrichment strategy for mitigating hydrate adhesion and blockage. Chemical Engineering Journal. ISSN 1385-8947. 453(2). doi: 10.1016/j.cej.2022.139918. Full text in Research Archive Show summary

  Unwanted gas hydrates blockage is a threat to the safety of oil-gas pipeline systems. Deploying passive anti-hydrate surfaces is a promising approach to circumventing the long-lasting hydrate problem, and a precise understanding of the interactions between hydrate and solid surfaces is a prerequisite for the creation of such surfaces. In this work, the underlying mechanisms and the key influencing factors of hydrate adhesion are explored by large-scale molecular dynamics simulations. Hydrates with an intermediate layer (IML) containing varied gas content are brought to contact with solid surfaces having different levels of wettability and roughness. It is found that the final IML structure is dictated by the gas concentration. Enriching gas content in the vicinity of solid surfaces is crucial for lowering hydrate adhesion strength. The results indicate that forming a molecular gas layer or gas bubbles on solid surfaces can enable the automatic detachment of the eventually formed hydrate on a pipeline wall surface under the action of shear flow. This study manifests our approach of utilizing an interfacial gas-enrichment strategy (IGES) for weakening hydrate adhesion as a novel passive anti-hydrate surface design.

• Fu, Ran; Xu, Yihua; Liu, Yisi; Lin, Yanwen; Xu, Ke & Chang, Yuanhao [Show all 9 contributors for this article] (2022). Thermally induced hex-graphene transitions in 2D carbon crystals. Nanotechnology Reviews. ISSN 2191-9089. 11(1), p. 1101–1114. doi: 10.1515/ntrev-2022-0066. Full text in Research Archive Show summary

  Resourceful beyond-graphene two-dimensional (2D) carbon crystals have been proposed/synthesized; however, the fundamental knowledge of their melting thermodynamics remains lacking. Here, the structural and thermodynamic properties of nine contemporary 2D carbon crystals upon heating are investigated using first-principle-based ReaxFF molecular dynamics simulations. Those 2D carbon crystals show distinct evolution of energetic and Lindemann index that distinguish their thermal stabilities. There are two or three critical temperatures at which structural transformation occurs for non-hexagon-contained 2D carbon allotropes. Analysis of polygons reveals that non-hexagon-contained 2D carbon crystals show thermally induced hex-graphene transitions via mechanisms such as bond rotations, dissociation, and reformation of bonds. The study provides new insights into the thermodynamics and pyrolysis chemistry of 2D carbon materials, as well as structural transitions, which is of great importance in the synthesis and application of 2D materials in high-temperature processing and environment.

• Chang, Yuanhao; Xiao, Senbo; Fu, Yuequn; Wang, Xiao; Zhang, Zhiliang & He, Jianying (2021). Nanomechanical Characteristics of Trapped Oil Droplets with Nanoparticles: A Molecular Dynamics Simulation. Journal of Petroleum Science and Engineering. ISSN 0920-4105. 203. doi: 10.1016/j.petrol.2021.108649. Full text in Research Archive Show summary

  Nanoparticles (NPs) possess great potentials in applications to enhanced oil recovery (EOR), the underlying mechanisms of which however remain to be explored. In this study, the motion of NPs and the local pressure distribution in a trapped oil droplet/nanofluid system in confined nanochannels are scrutinized by molecular dynamic simulations. Depending on the particle wettability, three different motion patterns have been observed: hydrophilic NPs are more likely to be adsorbed on the solid surface of the channel and stay close to the three-phase contact areas, hydrophobic NPs tend to move inside the oil droplet as clusters, and NPs with mixed hydrophobicity are prone to be trapped at the oil-water interface. It is shown that the existence of NPs introduces high local pressure in the nanochannels, especially at locations where NPs aggregate. Significantly, in the three-phase contact area for hydrophilic NPs, the local pressure distribution features the postulated structural disjoining pressure reported in the literature. For the first time, our molecular dynamics simulation results elucidate nanoparticle-induced structural disjoining pressure at the atomistic scale. The results thus provide a better understanding on the fundamentals of nanofluids in confined channels and serve as guidelines for the design of NPs for EOR applications.

• Liu, Siqi; Wan, Di; Guan, Shuai; Fu, Yuequn; Ren, Xiaobo & Zhang, Zhiliang [Show all 7 contributors for this article] (2021). Microstructure and nanomechanical behavior of an additively manufactured (CrCoNiFe)94Ti2Al4 high-entropy alloy. Materials Science & Engineering: A. ISSN 0921-5093. 823. doi: 10.1016/j.msea.2021.141737. Full text in Research Archive Show summary

  Recent substantial studies indicate that high-entropy alloys (HEAs) possess superior mechanical performance, including exceptional strength, high creep resistance, etc. However, additive manufacturing (AM), a burgeoning manufacturing method, may induce extraordinary impacts on the resulting mechanical properties. For the additively manufactured (AM-ed) HEAs, the nanoscale mechanical performance and deformation mechanisms in accordance with the microstructural properties remain unclear. In this work, the microstructure and nanomechanical properties of an AM-ed (CrCoNiFe)94Ti2Al4 HEA were investigated. The local mechanical properties including hardness, elastic modulus, and nanoscale creep deformation, were explored by nanoindentation-based measurement. Simultaneously, the crystallographic orientation dependence on the mechanical behavior of AM-ed HEA was carried out by combining with electron backscattered diffraction (EBSD). It is found that the {101}-grain has the highest hardness and elastic modulus, whereas the creep resistance of {111}-grain is the greatest, with the indicators of the creep mechanism showing lattice diffusion is the dominant mechanism. Two different states of HEA, as-printed and heat-treated, were utilized to explore the effect of heat treatment. Heat treatment in the current study can increase the hardness and elastic modulus but decrease the creep resistance slightly. This work elucidates the underlying mechanisms of grain orientation dependence on nanomechanical properties and the effects of heat treatment. Moreover, it also sheds light on the particular creep behavior at the nanoscale and creep mechanism of the AM-ed (CrCoNiFe)94Ti2Al4 HEA.

• Fu, Yuequn; Wu, Jianyang; Xiao, Senbo; Liu, Siqi; Zhang, Zhiliang & He, Jianying (2021). Tensile mechanical characteristics of ultra-thin carbon sulfur nanothreads in orientational order. Carbon. ISSN 0008-6223. 184, p. 146–155. doi: 10.1016/j.carbon.2021.08.006. Full text in Research Archive Show summary

  Carbon sulfur nanothreads (CSNTs) mainly composed of two chiral long alkane chains have been recently fabricated from thiophene by a pressure-induced phase transition in low-temperature, but their mechanical properties remain unexplored. Here, the critical roles of morphology and temperature on the tensile characteristics of CSNTs are for the first time examined using molecular dynamic simulations with first-principles-based ReaxFF forcefield. It is revealed that CSNTs exhibit high tensile Young’s modulus, high tensile strength and excellent ductility, and their tensile properties are morphology and temperature dependent. Morphologically, atomic arrangement with various configurations makes every CSNTs possess unique mechanical properties. Thermally, as temperature varies from 1-1500 K, CSNTs become mechanically weakened. In comparison with conventional diamond nanothreads (DNTs) and carbon nitride nanothreads (CNNTs), CSNTs show distinct axial elongation mechanisms, with relatively insignificant changes in chemical bond orders and bond length in the skeleton prior to the final rupture. Instead, the stretching of bond angle and dihedral angle mainly contribute to the global axial elongation, while the torsional deformation is limited due to their perfect global symmetry in the configuration. This study provides fundamental insights into the mechanics of ultra-thin CSNT structures.

• Liu, Siqi; Lin, Meichao; Wang, Xu; Fu, Yuequn; Ren, Xiaobo & Zhang, Zhiliang [Show all 7 contributors for this article] (2021). A framework for predicting the local stress-strain behaviors of additively manufactured multiphase alloys in the sequential layers. Materials Science & Engineering: A. ISSN 0921-5093. 832, p. 1–10. doi: 10.1016/j.msea.2021.142367. Full text in Research Archive Show summary

  The additive manufacturing (AM) process often results in non-uniform microstructure and different mechanical properties in sequential layers, impacting the overall performance of the AM-ed component. However, it is extremely challenging to evaluate the local stress-strain behavior of each individual layer, owing to the limited size of the AM-ed layered structure. To this end, a framework for characterizing and predicting the mechanical evolution of AM-ed multiphase alloys by combing nanoindentation and microstructure-based finite element method (FEM) was proposed. The sample used in this study was superduplex stainless steel (SDSS) manufactured by wire arc additive manufacturing (WAAM), and the microstructure varied from layer to layer. Firstly, the mechanical properties of the two constituent phases in each layer, including elastic modulus and hardness, were obtained by nanoindentation, and the indentation size effect (ISE) was also evaluated. The yield strength and hardening exponent of each phase were subsequently estimated by reverse analysis method, and therefore the constitutive behaviors of the individual phase, which served as input parameters for FEM, were acquired. By aid of real microstructure-based FEM under uniaxial tension, the overall stress-strain behaviors of each layer and the distributions of the stress and strain during the deformation process were investigated. This work provides a new avenue for the characterization of the multiphase alloys in AM industry, beneficial to the understanding of the mechanical evolution in AM-ed materials.

• Yang, Yu-Qi; Li, Liang; Wang, Xiang; Fu, Yuequn; He, Xiao-Qing & Zhang, Shi-Ling [Show all 7 contributors for this article] (2020). A Surfactant for Enhanced Heavy Oil Recovery in Carbonate Reservoirs in High-Salinity and High-Temperature Conditions. Energies. 13(17). doi: 10.3390/en13174525. Full text in Research Archive Show summary

  In view of the difficulty of producing heavy oil from carbonate reservoirs, the surfactant SDY-1 was synthesized by homogeneous solution polymerization with a homogeneous solution polymerization technique using aliphatic amine polyoxyethylene ether (PAEn) H(OCH2CH2)nNR(CH2CH2O)nH as the raw material, epichlorohydrin as the reaction intermediate, tetrabutylammonium bromide and pentamethyldivinyltriamine as the promoters, and alkylphenol as the catalyst. Based on the analysis of reservoir fluid and rock properties, the performance of the surfactant SDY-1 was evaluated in terms of its heat resistance, its salinity tolerance, its ability to change the heavy oil–water interfacial tension and rock wettability and its oil washing efficiency. The results show that when the salinity of the formation water is 2.23 × 105 mg/L, the addition of surfactant SDY-1 can lower the super-heavy oil–water interfacial tension with an asphaltene concentration of 30.19 wt.%, which is aged at a temperature of 140 °C for 3 days, from 22.41 to 0.366 mN/m. In addition, the surfactant SDY-1 can change the contact angle of super-heavy oil–water–rock from 129.7 to 67.4° and reduce the adhesion of crude oil to the rock surface by 99.26%. The oil displacement experiment indicates that the oil washing efficiency of the surfactant SDY-1 can reach 78.7% after ageing at a temperature of 140 °C for 3 days. Compared with petroleum sulfonate flooding, the addition of SDY-1 can improve the displacement efficiency by 33.6%, and the adsorption loss is only 0.651 mg/g oil sand. It has broad application prospects for heavy oil reservoirs with high temperatures, high pressures and high asphaltene contents.

• Fu, Yuequn; Xu, Ke; Wu, Jianyang; Zhang, Zhiliang & He, Jianying (2020). The effects of morphology and temperature on the tensile characteristics of carbon nitride nanothreads. Nanoscale. ISSN 2040-3364. 12(23), p. 12462–12475. doi: 10.1039/D0NR03206A. Full text in Research Archive Show summary

  Very recently synthesized carbon nitride nanothreads (CNNTs) by compressing crystalline pyridine show outperformance in chemical and physical properties over diamond nanothreads. Here, using first-principle based ReaxFF molecular dynamics (MD) simulations, a comprehensive investigation on mechanical characteristics of seven experimentally synthesized CNNTs is performed. All the CNNTs exhibit unique tensile properties that change with molecular morphology, atomic arrangement and the distribution of nitrogen in the skeleton. CNNTs with more effective loading covalent bonds at cross-sections are more mechanically robust. Surprisingly, tiny CNNT with periodic unit structures of 5462-cage shows extreme ductility because of formation of linear polymer via 4-step dissociation-and-reformation of bonds at extremely low temperature of 1 to 15 K, however, it yields by brittle failure at one cross-section with low ductility at higher temperature, similar to other CNNTs at different temperatures, which offers a feasible way to design a kind of lightweight material that can be used in ultra-low temperature conditions, for example, harsh deep space environment. Results also show that temperature significantly affects the fracture stress and rupture strain but not the effective stiffness. Analysis of atomic bond orders and bond lengthening reveals that the unique nonlinear elasticity of CNNTs is attributed to the occurrence of local bond transformations. This study provides physical insights into the tensile characteristics of CNNTs for design and application of the CNNT-based nanostructures as multifunctional materials.

• Fu, Yuequn; Xiao, Senbo; Liu, Siqi; Wu, Jianyang; Wang, Xiao & Qiao, Lijie [Show all 8 contributors for this article] (2020). Stability, deformation and rupture of Janus oligomer enabled self-emulsifying water-in-oil microemulsion droplets. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 22(43), p. 24907–24916. doi: 10.1039/d0cp03092a. Full text in Research Archive Show summary

  Microemulsion exists widely in nature, daily life and industrial manufacturing, including petroleum production, food processing, drug delivery, new materials fabrication, sewage treatment, etc. The mechanical properties of microemulsion droplets and the correlation to their molecular structures are of vital importance to those applications. Despite researches on their physicochemical determinants, there are lots of challenges to explore mechanical properties of microemulsion by experimental studies. Herein, atomistic modelling was utilized to study the stability, deformation, and rupture of Janus oligomer enabled water-in-oil microemulsion droplets, aiming for revealing their intrinsic relationship to the Janus oligomer based surfactants and oil structures. The self-emulsifying process from a water, oil and surfactant mixture to a single microemulsion droplet was modulated by the amphiphilicity and the structure of the surfactants. Four microemulsion systems with interfacial thickness in the range of 7.4-17.3Å were self-assembled to explore the effect of the surfactant on the droplet morphology. By applying counter forces on the water core and the surfactant shell, the mechanical stability of microemulsion droplets was probed at different ambient temperatures. A strengthening response and a softening regime before and after a temperature-dependent peak force were identified followed by final rupture. This work demonstrates a practical strategy to precisely tune mechanical properties of a single microemulsion droplet, which can be applied in the formation, demulsification, and design of microemulsion in oil recovery and production, drug delivery and many other applications.

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• Fu, Yuequn (2023). Nano-Cavitation dynamics on the silica substrate. Full text in Research Archive
• Fu, Yuequn; Senbo, Xiao; Jianying, He & Zhiliang, Zhang (2019). Deformation mechanics of microemulsion droplets by atomistic modeling. Full text in Research Archive
• Fu, Yuequn; Senbo, Xiao; Jianying, He & Zhiliang, Zhang (2019). Mechanical properties of microemulsion droplet from a atomistic simulations. Full text in Research Archive
• Fu, Yuequn; He, Jianying & Zhang, Zhiliang (2021). Atomistic Insights to Interfacial Dynamics. Norges teknisk-naturvitenskapelige universitet. ISSN 9788232668946. Full text in Research Archive

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