Mingyang Chen

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Chen

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Mingyang

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0000-0003-4881-8875

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Publications 1 - 9 of 9

A Poromechanical Model for Sorption Hysteresis in Nanoporous Polymers
Chen, Mingyang; Coasne, Benoit; Guyer, Robert; et al. (2020)
The Journal of Physical Chemistry B
Sorption hysteresis in nanoporous polymer is an intriguing phenomenon that involves coupling between sorption and deformation. Based on the mechanism revealed at the microscopic level by use of molecular simulation, a poromechanical model is developed capturing all relevant physics and yielding a quantitative description. In this model, the coupling between sorption and deformation is described by a poromechanics framework. More in detail, an upscaling process from the molecular mechanism is implemented to model the hysteresis through the state change of each element upon deformation. We provide two solutions of the model: a numerical one based on the finite element method and an analytical one based on uniform strain assumption. The results from both solutions agree well with the molecular simulation and experimental results, therefore capturing and describing adequately sorption hysteresis. The developed model illustrates that water forms different structural distributions upon adsorption and desorption. A parametric study shows that sorption hysteresis is influenced by material properties. We find that a softer material with stronger adsorbent–adsorbate interaction tends to exhibit more profound sorption hysteresis. The developed model, which relies on the concepts of sorption–deformation coupling and multiscale modeling from atomistic simulations to domain dependent theory, paves the way for a new direction of modeling sorption hysteresis.
Hygromechanics of softwood cellulosic nanocomposite with intermolecular interactions at fiber-matrix interface investigated with molecular dynamics
Zhang, Chi; Chen, Mingyang; Coasne, Benoit; et al. (2022)
Composites Part B: Engineering
Intermolecular interactions at the fiber-matrix interface strongly affect the hygromechanical behavior and overall mechanical performance of hydrophilic cellulosic nanocomposites. The mechanics of a model interface consisting of cellulose and galactoglucomannan, inspired by the natural material wood, is investigated by molecular simulations over the full hydration range. With the increment of moisture content, the composite swells anisotropically and non-monotonically with an initial shrinkage. The interphase, a 1–2 nm thick region of matrix strongly influenced by the fiber, shows features of enrichment and ordered structure distinct from bulk. Pulling tests reveal the interfacial shear strength as a function of moisture content. The stick-slip behavior is explained by the strong correlation between the number of hydrogen bonds and the interfacial shear stress, suggesting the force rendered by a single hydrogen bond to be ∼140 pN. These insights shed light on the mechanics of interface and interphase, a topic of less attention yet critical for understanding the mechanical performance of fiber-reinforced composites.
Hygromechanical mechanisms of wood cell wall revealed by molecular modeling and mixture rule analysis
Zhang, Chi; Chen, Mingyang; Keten, Sinan; et al. (2021)
Science Advances
Despite the thousands of years of wood utilization, the mechanisms of wood hygromechanics remain barely elucidated, owing to the nanoscopic system size and highly coupled physics. This study uses molecular dynamics simulations to systematically characterize wood polymers, their mixtures, interface, and composites, yielding an unprecedented micromechanical dataset including swelling, mechanical weakening, and hydrogen bonding, over the full hydration range. The rich data reveal the mechanism of wood cell wall hygromechanics: Cellulose fiber dominates the mechanics of cell wall along the longitudinal direction. Hemicellulose glues lignin and cellulose fiber together defining the cell wall mechanics along the transverse direction, and water severely disturbs the hemicellulose-related hydrogen bonds. In contrast, lignin is rather hydration independent and serves mainly as a space filler. The moisture-induced highly anisotropic swelling and weakening of wood cell wall is governed by the interplay of cellulose reinforcement, mechanical degradation of matrix, and fiber-matrix interface.
Molecular Simulation of Sorption-Induced Deformation in Atomistic Nanoporous Materials
Chen, Mingyang; Coasne, Benoit; Guyer, Robert; et al. (2019)
Langmuir
Role of cellulose nanocrystals on hysteretic sorption and deformation of nanocomposites
Chen, Mingyang; Coasne, Benoit; Derome, Dominique; et al. (2020)
Cellulose
A molecular model of an all-cellulose nanocomposite, with an amorphous cellulose matrix reinforced by cellulose nanocrystals, is built to study the role of cellulose nanocrystal (CN) as a nanofiller in the coupled behavior between sorption and deformation. We find two competitive mechanisms. The first mechanism is the reinforcing effect through CN-matrix mechanical interaction, which constrains the sorption-induced swelling of the matrix and results in a reduction of sorption amount and of hysteresis in both sorption and deformation. The second mechanism is the CN-water interaction, enhancing water sorption in the matrix at the CN-matrix interface, increasing the sorption-induced swelling of the matrix, and increasing the resulting hysteresis in sorption and deformation. The final gain/reduction in sorption, swelling and related hysteresis depends on which of the two effects prevails. These findings shed light on the tailoring of cellulose-based composites for applications involving sorption and deformation. © 2020, Springer Nature B.V.
Moisture-induced deformations of wood and shape memory
Zhang, Chi; Chen, Mingyang; Derome, Dominique; et al. (2021)
Journal of Physics: Conference Series
Wood is known to swell substantially during moisture adsorption and shrink during desorption. These deformations may lead to wood damage in the form of cracking and disjoining of wooden components in e.g. floor or windows. Two swelling mechanisms may be distinguished: reversible swelling/shrinkage and moisture-induced shape memory effect. In the latter, wood is deformed in the wet state and afterward dried under maintained deformation, in order that wood retains its deformed shape even after the removal of the mechanical loading, called fixation. When wood is wetted again, it loses its fixation, partially regains its original shape, called recovery. These two mechanisms have their origin at the nanoscale and are modelled here using atomistic simulation and after upscaled to continuum level allowing finite element modelling. Hysteretic sorption and swelling are explained at nanoscale by the opening and closing of sorption sites in ad- and desorption, where in desorption water molecules preferentially remained bonded at sorption sites. The moisture-induced shape memory is explained by the moisture-induced activation of the interfaces between the reinforcing crystalline cellulose fibres and its matrix at nanoscale, referred to as a molecular switch. Our work aims to highlight that the understanding of sorption-induced reversible deformation and moisture-induced shape memory may play an important role in wood engineering and in building physics applications.
Wood-Moisture Relationships Studied with Molecular Simulations: Methodological Guidelines
Chen, Mingyang; Zhang, Chi; Shomali, Ali; et al. (2019)
Forests
This paper aims at providing a methodological framework for investigating wood polymers using atomistic modeling, namely, molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. Atomistic simulations are used to mimic water adsorption and desorption in amorphous polymers, make observations on swelling, mechanical softening, and on hysteresis. This hygromechanical behavior, as observed in particular from the breaking and reforming of hydrogen bonds, is related to the behavior of more complex polymeric composites. Wood is a hierarchical material, where the origin of wood-moisture relationships lies at the nanoporous material scale. As water molecules are adsorbed into the hydrophilic matrix in the cell walls, the induced fluid–solid interaction forces result in swelling of these cell walls. The interaction of the composite polymeric material, that is the layer S2 of the wood cell wall, with water is known to rearrange its internal material structure, which makes it moisture sensitive, influencing its physical properties. In-depth studies of the coupled effects of water sorption on hygric and mechanical properties of different polymeric components can be performed with atomistic modeling. The paper covers the main components of knowledge and good practice for such simulations.
Coupling of sorption and deformation in soft nanoporous polymers: Molecular simulation and poromechanics
Chen, Mingyang; Coasne, Benoit; Derome, Dominique; et al. (2020)
Journal of the Mechanics and Physics of Solids
Sorption-Induced Deformation of Nanoporous Materials
Chen, Mingyang (2019)
Sorption-induced deformation is ubiquitous in nanoporous media, but underlying mechanisms are not yet fully understood, and a reliable modeling of this phenomenon is absent. Moreover hysteresis in sorption and swelling isotherms is observed but its origin not yet fully understood and not modeled. In this thesis the sorption-induced deformation of nanoporous media is studied systematically with different approaches. Three different nanoporous materials are considered: microporous polymers, microporous polymer-based composites and mesoporous materials. With the help of molecular simulations, the coupling mechanisms between sorption and deformation are revealed and the sorption and strain isotherms, as well as their hysteresis, are quantitatively modeled. With the knowledge gained at molecular level, a macroscopic description of sorption-induced deformation is given with the help of a dependent domain model. Molecular simulations demonstrate that microporous polymers swell upon water sorption as water molecules have a tendency to create more space between the flexible polymer chains for accommodating their presence. Sorption hysteresis is found to be related to deformation: polymers swell to form water–polymer hydrogen bonds upon adsorption but these bonds do not break upon desorption at the same chemical potential, which leads to sorption hysteresis. This hysteresis also manifests itself in other physical properties such as heat of sorption and bulk modulus. The influence of temperature and stress state on the coupled behavior is also examined. It is found that, when relating observable variables to the correct independent variables, hysteresis disappears as such explaining the actual origin of hysteresis. As a statement, hysteresis does not exist when looking at it from the correct driving potential. With the knowledge acquired on the bulk microporous polymer, the sorption-induced deformation of a microporous polymer-based composite, with cellulose nanocrystal (CN) as reinforcement and amorphous cellulose (AC) as matrix, is studied. Two competitive mechanisms are found regarding the coupling between sorption and deformation. The first mechanism is the reinforcing effect through CN-AC mechanical interaction, which constrains the sorption-induced swelling of the matrix and results in a reduction of sorption amount and of hysteresis in both sorption and deformation. The second mechanism is the CN-water interaction, enhancing water sorption in the matrix at the CN-matrix interface, increasing the sorption-induced swelling of the matrix and increasing the resulting hysteresis in sorption and deformation. Sorption-induced deformation in mesoporous materials is studied at single pore level with two atomistic models, a slit pore and a cylindrical pore. Two driving mechanisms are revealed for both slit and cylindrical pore models. At high relative vapor pressure, pore deformation is governed by Laplace pressure as the pore gets filled with liquid due to capillary condensation. At low pressure, when liquid films are formed on the pore surfaces and the pore remains mainly filled by vapor phase, the strain is driven by the attractive solid-fluid forces and the in-plane pressure within the film. Because of the interplay of these deformation mechanisms, the strain changes from shrinkage to expansion upon increase of pressure. The thesis ends with a Dependent Domain Model (DDM), developed to describe the coupled behavior at the macroscale of microporous polymers. The DDM is based on poromechanics taking into account the mechanical behavior of the solid and the influence of different pore sizes. The proposed dependent domain model captures the governing mechanism of the coupled behavior and provides a deeper understanding in sorption-induced deformation. Sorption-induced deformation is simulated and addressed systematically in this thesis regarding different materials, different coupling mechanisms and different scales. The simulation results agree with experiments and the proposed mechanism can explain the experimental results well. The outcome of this research provides a theoretical framework for modeling sorption-induced deformation of a great variety of nanoporous materials. Though the emphasis is laid at molecular scale, an upscaling approach is provided to connect the information at different scales.

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