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Molecular mechanism of adsorption/desorption hysteresis:dynamics of shale gas in nanopores

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Science China(Physics,Mechanics & Astronomy) 2017年第1期60卷 24-31页

作者： Jie Chen FengChao Wang He Liu hengan wu CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern Mechanics University of Science and Technology of China Hefei 230027 China PetroChina Research Institute of Petroleum Exploration & Development Beijing 100083 China

Understanding the adsorption and desorption behavior of methane has received considerable attention since it is one of the crucial aspects of the exploitation of shale ***,obvious hysteresis is observed from the ideally reversible physical sorption of methane in some ***,the underlying mechanism still remains an open *** this study,Monte Carlo(MC) and molecular dynamics(MD) simulations are carried out to explore the molecular mechanisms of adsorption/desorption ***,a detailed analysis about the capillary condensation of methane in micropores is *** influence of pore width,surface strength,and temperature on the hysteresis loop is further *** is found that a disappearance of hysteresis occurs above a temperature *** with the phase diagram of methane,we explicitly point out that capillary condensation is inapplicable for the hysteresis of shale gas under normal temperature ***,a new mechanism,variation of pore throat size,is proposed and *** methane to pass through the throat,a certain energy is required due to the repulsive *** required energy increases with shrinkage of the throat,such that the originally adsorbed methane cannot escape through the narrowed *** trapped methane molecules account for the ***,the hysteresis loop is found to increase with the increasing pressure and decreasing *** suggest that the variation of pore throat size can explain the adsorption/desorption hysteresis of shale *** conclusions and findings are of great significance for guiding the efficient exploitation of shale gas.

关键词： shale gas adsorption/desorption hysteresis numerical simulation capillary condensation pore throat

Molecular levers enable anomalously enhanced strength and toughness of cellulose nanocrystal at cryogenic temperature

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Nano Research 2023年第5期16卷 8036-8041页

作者： YuanZhen Hou Jun Xia ZeZhou He YinBo Zhu hengan wu CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern MechanicsCAS Center for Excellence in Complex System MechanicsUniversity of Science and Technology of ChinaHefei 230027China Faculty of Civil Engineering and Mechanics Jiangsu UniversityZhenjiang 212013China

The quest for widespread applications especially in extreme environments accentuates the necessity to design materials with robust mechanical and thermodynamic *** all existing materials yield temperature-variant mechanical properties,essentially determined by their different atomic bonding *** general,weak non-covalent interactions are considered to diminish the structural anti-destabilization of covalent crystals despite the toughening ***,starting from multiscale theoretical modeling,we herein reveal an anomalous stabilizing effect in cellulose nanocrystals(CNCs)by the cooperation between the non-covalent hydrogen bonds and covalent glucosidic skeleton,namely molecular levers(MLs).It is surprising to find that the hydrogen bonds in MLs behave like covalent bindings under cryogenic conditions,which provide anomalously enhanced strength and toughness for *** analyses demonstrate that the unique dynamical mechanical behaviors from ambient to deep cryogenic temperatures are synergetic results of the intrinsic temperature dependence veiled in MLs and the overall thermo-induced CNC destabilization/*** the consequence,the variation trend of mechanical strength exhibits a bilinear temperature dependence with~77 K as the turning *** underlying investigations not only establish the bottom–up interrelations from the hydrogen bonding thermodynamics to the crystal-scale mechanical properties,but also facilitate the potential application of cellulose-based materials at extremely low temperatures such as those in outer space.

关键词： cellulose nanocrystal molecular lever thermodynamic stability thermo-mechanical behavior cryogenic temperature

Molecular kinetic theory of boundary slip on textured surfaces by molecular dynamics simulations

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Science China(Physics,Mechanics & Astronomy) 2014年第11期57卷 2152-2160页

作者： WANG LiYa WANG FengChao YANG FuQian wu hengan CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern MechanicsUniversity of Science and Technology of China Materials Program Department of Chemical and Materials EngineeringUniversity of Kentucky

A theoretical model extended from the Frenkel-Eyring molecular kinetic theory(MKT)was applied to describe the boundary slip on textured *** concept of the equivalent depth of potential well was adopted to characterize the solid-liquid interactions on the textured *** slip behaviors on both chemically and topographically textured surfaces were investigated using molecular dynamics(MD)*** extended MKT slip model is validated by our MD simulations under various situations,by constructing different complex surfaces and varying the surface wettability as well as the shear stress exerted on the *** slip model can provide more comprehensive understanding of the liquid flow on atomic scale by considering the influence of the solid-liquid interactions and the applied shear stress on the ***,the slip velocity shear-rate dependence can be predicted using this slip model,since the nonlinear increase of the slip velocity under high shear stress can be approximated by a hyperbolic sine function.

关键词： constructing validated chemically zigzag considering hyperbolic fitting rectangular fitted Frenkel

Multiscale mechanics of noncovalent interface in graphene oxide layered nanocomposites

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Theoretical & Applied Mechanics Letters 2022年第1期12卷 3-9页

作者： ZeZhou He YinBo Zhu hengan wu CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern MechanicsCAS Center for Excellence in Complex System MechanicsUniversity of Science and Technology of ChinaHefei 230027China

Noncovalent interfaces play a vital role in inelastic deformation and toughening mechanisms in layered nanocomposites due to their dynamical recoverability. When interfacial engineering is applied to design layered nanocomposites, shear-lag analysis is usually implemented to evaluate the capability of interfacial loading transfer. Here, we introduce a multiscale shear-lag model that correlates macroscale mechanical properties with the molecular mechanisms to quantify the effects of interfacial configuration in graphene oxide(GO) layered nanocomposites. By investigating the mechanical responses of commensurate and incommensurate interfaces, we identify that the commensurate interface exhibits a pronounced size effect due to the nucleation and propagation of interfacial defects, whereas the incommensurate interface displays uniform deformation. Our predictions are further validated through large-scale molecular dynamics simulations for GO layered nanocomposites. This work demonstrates how size effects and interfacial configurations can be exploited to fabricate layered nanocomposites with superior mechanical properties despite relying on weak noncovalent interfaces.

关键词： Multiscale mechanics Noncovalent interface Commensurate and incommensurate Shear-lag model Layered nanocomposites

Molecular transport under extreme confinement

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Science China(Physics,Mechanics & Astronomy) 2022年第6期65卷 1-10页

作者： FengChao Wang JianHao Qian JingCun Fan JinChuan Li HengYu Xu hengan wu CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern MechanicsCAS Center for Excellence in Complex System MechanicsUniversity of Science and Technology of ChinaHefei 230027China

Mass transport through the nanoporous medium is ubiquitous in nature and *** the macroscale transport phenomena which have been well understood by the theory of continuum mechanics,the relevant physics and mechanics on the nanoscale transport still remain *** developments in fabrication of slit-like nanocapillaries with precise dimensions and atomically smooth surfaces have promoted the fundamental research on the molecular transport under extreme *** this review,we summarized the contemporary progress in the study of confined molecular transport of water,ions and gases,based on both experiments and molecular dynamics *** liquid exhibits a pronounced layered structure that extends over several intermolecular distances from the solid surface,which has a substantial influence on static properties and transport behaviors under *** studies have also shown that those molecular details could provide some new understanding on the century-old classical theory in this field.

关键词： confined mass transport nanocapillary solid-liquid interface confinement effect

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Production analysis in shale gas reservoirs based on fracturing-enhanced permeability areas

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Science China(Physics,Mechanics & Astronomy) 2019年第10期62卷 103-111页

作者： Chuang Liu YongKuan Shen JiaNing Zhang DeTang Lu He Liu hengan wu Chinese Academy of Sciences Key Laboratory ofMechanical Behavior and Design of Materials Department of Modern MechanicsUniversity of Science and Technology of ChinaHefei 230027China Hefei Guoxuan High-Tech Power Energy Company Hefei 230001China Petro China Research Institute of Petroleum Exploration&Development Beijing 100083China

Hydraulic fracturing has been widely applied in shale gas exploitation because it improves the permeability of the rock *** stimulation parameters such as the pumping rate, the fracturing sequence, and the fracture spacing significantly influence the distribution of the stimulated reservoir volume(SRV). In this research, we built a numerical model that incorporates the hydraulic fracturing process and predicts gas production. The simulation of fracture propagation is based on the extended finite element method(XFEM), which helps to calculate aspects of the fractures and the SRV; we imported the results into a production analysis model as the initial conditions for production prediction. Using the model, we investigated the effects of some key parameters such as rock cohesion, fracture spacing, pumping rate, and fracturing sequence on the shale gas *** results proved that the SRV was distributed in the vicinity of the main fractures, and the SRVs were connected between the fractures in a small fracture spacing. We obtained optimal spacing by analyzing the production increment. High pumping-rate treatment greatly changes the in-situ stress around the hydraulic fractures and enlarges the field of SRV. Simultaneous fracturing treatment improves the flow conductivity of formation more than sequential fracturing. This study provides insights into the hydraulic fracturing design for economical production.

关键词： shale gas production prediction numerical simulation enhanced permeability area hydraulic fracturing

Molecular dynamics studies on spreading of nanofluids promoted by nanoparticle adsorption on solid surface

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Theoretical & Applied Mechanics Letters 2013年第5期3卷 31-34页

作者： Fengchao Wang hengan wu CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern MechanicsUniversity of Science and Technology of China

Abstract Spreading of nanofluids on solid substrate was studied via molecular dynamics simulations. Simulation models for two immiscible fluids （oil and water based nanofiuids） confined in a slit between two planar solid walls were set up. The influence of the volume concentration of the nanoparticles on the three-phase contact line motion was investigated. We found that the larger volume concentration results in more visible nanoparticle adsorption on solid surface. This effect further induces an advancing displacement of the contact line compared with the meniscus profiles in low concentration case and that with the absence of nanoparticles. These findings are consistent with the previous experimental and theoretical results and provide the atomic-scale understanding on nanofluid spreading.

关键词： nanofluids three-phase contact line spreading nanoparticles molecular dynamics sim-ulations

A strategy to drive nanoflow using Laplace pressure and the end effect

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Droplet 2024年第3期3卷 107-113页

作者： Keli Zhang Hengyu Xu Jingcun Fan Cancan Ouyang hengan wu Fengchao Wang CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern MechanicsUniversity of Science and Technology of ChinaHefeiChina

Nanofluidics holds significant potential across diverse fields,including energy,environ-ment,and ***,the fundamental driving mechanisms on the nanoscale remain elusive,underscoring the crucial importance of exploring nanoscale driving *** study introduces a Laplace pressure-driven flow method that is accurately controlled and does not interfere with interfacial ***,we first confirmed the applicability of the Young–Laplace equation for droplet radii ranging from 1 to 10 *** that,a steady-state liquid flow within the carbon nanotube was attained in molecular dynamics *** flow was driven by the Laplace pressure difference across the nanochannel,which originated from two liquid droplets of unequal sizes positioned at the channel ends,***,we employ the Sampson formula to rectify the end effect,ultimately deriving a theoretical model to quantify the flow rate,which satisfactorily describes the molecular dynamics simu-lation *** research enhances our understanding on the driving mechanisms of nanoflows,providing valuable insights for further exploration in fluid dynamics on the nanoscale.

关键词： flow holds satis

Interfacial ion regulation on 2D layered double hydroxide nanosheets for enhanced thermal insulation

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Science China Chemistry 2022年第5期65卷 898-904页

作者： Chun Wang Hengyu Xu Han Cheng Hao Yu Si Liu Wenjie Wang Ruilin Yuan Hongfei Liu Tianpei Zhou Wangsheng Chu hengan wu Yi Xie Changzheng wu Hefei National Laboratory for Physical Sciences at the Microscale University of Science and Technology of ChinaCAS Center for Excellence in Nanoscienceand CAS Key Laboratory of Mechanical Behavior and Design of MaterialsHefei 230026China CAS Key Laboratory of Mechanical Behavior and Design of Materials Department of Modern MechanicsCAS Center for Excellence in Complex System Mechanics University of Science and Technology of ChinaHefei 230027China National Synchrotron Radiation Laboratory University of Science and Technology of ChinaHefei 230029China Institute of Energy Hefei Comprehensive National Science CenterHefei 230031China

Exploring new strategies to broaden the upper/lower limit of thermal conductivity is of great interest to develop thermal management materials that can adapt to extreme *** this work,we employ an interfacial ion regulation to enhance the thermal insulation performance of 2D layered double hydroxide *** introduction of interfacial ion enlarges the interplanar spacing of Co(OH)_(2) nanosheets from 4.64 to 8.05 ?,which reduces phonon scattering length perpendicular to the two-dimensional plane and leads to enhanced interlayer thermal *** interfacial ion-regulated Co(OH)_(2)(named as Co(OH)_(2)-M^(x-)) exhibits 3-fold enhancement of thermal insulation through decreasing the thermal conductivity to as low as 0.15 W m^(-1) K^(-1),which is among the top values in 2D solid *** anticipate that interfacial ion regulation for 2D nanosheets paves a new avenue to break through the thermal insulation limit.

关键词： two dimensional materials interfacial ion regulation thermal conductivity phonon scattering