Research

14 pages, 3532 KiB

Open AccessArticle

Molecular Dynamics Study on Mechanical Properties of Interface between Urea-Formaldehyde Resin and Calcium-Silicate-Hydrates

by Xianfeng Wang, Wei Xie, Taoran Li, Jun Ren, Jihua Zhu, Ningxu Han and Feng Xing

Materials 2020, 13(18), 4054; https://doi.org/10.3390/ma13184054 - 12 Sep 2020

Cited by 10 | Viewed by 2502

Abstract

Microcapsule based self-healing concrete can automatically repair damage and improve the durability of concrete structures, the performance of which depends on the binding behavior between the microcapsule wall and cement matrix. However, conventional experimental methods could not provide detailed information on a microscopic [...] Read more.

Microcapsule based self-healing concrete can automatically repair damage and improve the durability of concrete structures, the performance of which depends on the binding behavior between the microcapsule wall and cement matrix. However, conventional experimental methods could not provide detailed information on a microscopic level. In this paper, through molecular dynamics simulation, three composite models of Tobermorite (Tobermorite 9 Å, Tobermorite 11 Å, Tobermorite 14 Å), a mineral similar to Calcium-Silicate–Hydrate (C–S–H) gel, with the linear urea–formaldehyde (UF), the shell of the microcapsule, were established to investigate the mechanical properties and interface binding behaviour of the Tobermorite/UF composite. The results showed that the Young’s modulus, shear modulus and bulk modulus of Tobermorite/UF were lower than that of ‘pure’ Tobermorite, whereas the tensile strength and failure strain of Tobermorite/UF were higher than that of ‘pure’ Tobermorite. Moreover, through radial distribution function (RDF) analysis, the connection between Tobermorite and UF found a strong interaction between Ca, N, and O, whereas Si from Tobermorite and N from UF did not contribute to the interface binding strength. Finally, high binding energy between the Tobermorite and UF was observed. The research results should provide insights into the interface behavior between the microcapsule wall and the cement matrix. Full article

(This article belongs to the Special Issue Molecular Dynamics in Nanomaterials and Nanofluids)

► Show Figures

Figure 1

11 pages, 2530 KiB

Open AccessArticle

The Effect of Co-Doping at the A-Site on the Structure and Oxide Ion Conductivity in (Ba_0.5−xSr_x)La_0.5InO_3−δ: A Molecular Dynamics Study

by Kuk-Jin Hwang, Hae-Jin Hwang, Myung-Hyun Lee, Seong-Min Jeong and Tae Ho Shin

Materials 2019, 12(22), 3739; https://doi.org/10.3390/ma12223739 - 13 Nov 2019

Cited by 1 | Viewed by 2219

Abstract

A molecular dynamics simulation was used to investigate the structural and transport properties of a (Ba_0.5−xSr_x)La_0.5InO_3−δ (x = 0, 0.1, 0.2) oxygen ion conductor. Previous studies reported that the ionic conductivity of Ba-doped LaInO₃ decreases [...] Read more.

A molecular dynamics simulation was used to investigate the structural and transport properties of a (Ba_0.5−xSr_x)La_0.5InO_3−δ (x = 0, 0.1, 0.2) oxygen ion conductor. Previous studies reported that the ionic conductivity of Ba-doped LaInO₃ decreases because Ba dopant forms a narrow oxygen path in the lattice, which could hinder the diffusion of oxygen ions. In this study, we reveal the mechanism to improve ionic conductivity by Ba and Sr co-doping on an La site in LaInO₃ perovskite oxide. The results show that the ionic conductivity of (Ba_0.5−xSr_x)La_0.5InO_3−δ increases with an increasing number of Sr ions because oxygen diffusion paths which contain Sr ions have a larger critical radius than those containing Ba ions. The radial distribution function (RDF) calculations show that the peak heights in compositions including Sr ions were lower and broadened, meaning that the oxygen ions moved easily into other oxygen sites. Full article

(This article belongs to the Special Issue Molecular Dynamics in Nanomaterials and Nanofluids)

► Show Figures

Figure 1

9 pages, 1921 KiB

Open AccessArticle

The Energy Storage Properties of Refrigerants (R170, R134a, R143a, and R152a) in Mof-5 Nanoparticles: A Molecular Simulation Approach

by Qiang Wang, Zhengyong Huang, Shucheng Ou and Ruiqiang Zhang

Materials 2019, 12(21), 3577; https://doi.org/10.3390/ma12213577 - 31 Oct 2019

Cited by 4 | Viewed by 2958

Abstract

The thermophysical properties of refrigerant can be modified via adding solid materials to it. In this paper, molecular simulations and thermodynamic calculations were employed to investigate the adsorption and energy storage of ethane (R170), 1,1,1,2-tetrafluoroethane (R134a), 1,1,1-trifluoroethane (R143a), and 1,1-difluoroethane (R152a) in metal [...] Read more.

The thermophysical properties of refrigerant can be modified via adding solid materials to it. In this paper, molecular simulations and thermodynamic calculations were employed to investigate the adsorption and energy storage of ethane (R170), 1,1,1,2-tetrafluoroethane (R134a), 1,1,1-trifluoroethane (R143a), and 1,1-difluoroethane (R152a) in metal organic framework (MOF)-5 nanoparticles. The results show that the fluorine atom in the refrigerants will strengthen the adsorption of refrigerants in MOF-5. However, the fluorine-free refrigerant, R170, owns larger enthalpy difference of desorption than the other refrigerants with fluorine under high pressure. The thermal energy storage capacity of the refrigerant/MOF-5 mixture is larger than that of the pure refrigerant at low pressure. Also, the negative enhancement of the energy storage property of the mixture is found in some cases when the refrigerant experiences phase transition. Full article

(This article belongs to the Special Issue Molecular Dynamics in Nanomaterials and Nanofluids)

► Show Figures

Figure 1

15 pages, 3651 KiB

Open AccessArticle

Effect of Water on the Dynamic Tensile Mechanical Properties of Calcium Silicate Hydrate: Based on Molecular Dynamics Simulation

by Jikai Zhou and Yuanzhi Liang

Materials 2019, 12(17), 2837; https://doi.org/10.3390/ma12172837 - 03 Sep 2019

Cited by 28 | Viewed by 3110

Abstract

To study the effect of water on the dynamic mechanical properties of calcium silicate hydrate (C–S–H) at the atomic scale, the molecular dynamics simulations were performed in uniaxial tension with different strain rates for C–S–H with a degree of saturation from 0% to [...] Read more.

To study the effect of water on the dynamic mechanical properties of calcium silicate hydrate (C–S–H) at the atomic scale, the molecular dynamics simulations were performed in uniaxial tension with different strain rates for C–S–H with a degree of saturation from 0% to 100%. Our calculations demonstrate that the dynamic tensile mechanical properties of C–S–H decrease with increasing water content and increase with increasing strain rates. With an increase in the degree of saturation, the strain rate sensitivity of C–S–H tends to increase. According to Morse potential function, the tensile stress-strain relationship curves of C–S–H are decomposed and fitted, and the dynamic tensile constitutive relationship of C–S–H considering the effect of water content is proposed. This reveals the strain rate effect of the cementitious materials with different water content from molecular insights, and the dynamic constitutive relationship obtained in this paper is necessary to the modelling of cementitious materials at the meso-scale. Full article

(This article belongs to the Special Issue Molecular Dynamics in Nanomaterials and Nanofluids)

► Show Figures

Figure 1

11 pages, 9657 KiB

Open AccessArticle

Molecular Dynamics Simulations of Atomic Diffusion during the Al–Cu Ultrasonic Welding Process

by Jingwei Yang, Jie Zhang and Jian Qiao

Materials 2019, 12(14), 2306; https://doi.org/10.3390/ma12142306 - 19 Jul 2019

Cited by 31 | Viewed by 5238

Abstract

Ultrasonic welding (UW) is an important joining technique in the electrical industry. Molecular dynamic simulation has been shown to possess several advantages for revealing the evolution of the atomic-scale structure and the interpretation of diffusion mechanisms at the microscopic level. However, voids associated [...] Read more.

Ultrasonic welding (UW) is an important joining technique in the electrical industry. Molecular dynamic simulation has been shown to possess several advantages for revealing the evolution of the atomic-scale structure and the interpretation of diffusion mechanisms at the microscopic level. However, voids associated with the understanding of microstructure evolution in the weld zone and dynamic processes that occur during ultrasonically welded materials still exist, and no UW studies at the atomic scale have so far been reported. In this study, molecular dynamic simulations of UW between Al and Cu were performed to investigate the diffusion behaviors of Al and Cu atoms. The results confirmed the occurrence of asymmetrical diffusion at the Al/Cu interface during UW. Meanwhile, recovery was noticed in the disordered Al blocks at low temperature. The thickness of the diffusion layer increased with the welding time. For relatively long welding times (1 ns), the concentrations of Al and Cu revealed the appearance of phase transitions. In addition, the diffusion during UW was identified as a dynamic and unsteady process. The diffusion coefficient was much larger than that underwent during the steady diffusion process despite the low interfacial temperature (below 375 K), which was mainly attributed to shear plastic deformation at the interface. Full article

(This article belongs to the Special Issue Molecular Dynamics in Nanomaterials and Nanofluids)

► Show Figures

Figure 1

10 pages, 3032 KiB

Open AccessArticle

The Effect and Associate Mechanism of Nano SiO₂ Particles on the Diffusion Behavior of Water in Insulating Oil

by Wenxin Tian, Chao Tang, Qian Wang, Shiling Zhang and Yali Yang

Materials 2018, 11(12), 2373; https://doi.org/10.3390/ma11122373 - 26 Nov 2018

Cited by 23 | Viewed by 3957

Abstract

Moisture has a significant effect on the internal insulation performance of transformers, and is closely related to the breakdown voltage of transformer insulating oil. In the present work, we studied the effect of nano-SiO₂ particles on the diffusion of water in insulating [...] Read more.

Moisture has a significant effect on the internal insulation performance of transformers, and is closely related to the breakdown voltage of transformer insulating oil. In the present work, we studied the effect of nano-SiO₂ particles on the diffusion of water in insulating naphthenic mineral oil using molecular dynamics simulation. Six models were established, three of which contained nano-SiO₂ particles together with water concentration of 1 wt.%, 2 wt.%, or 3 wt.%. For each model variations in free volume, mean square displacement, and interaction energy were assessed. The addition of nano SiO₂ particles was found to reduce the free volume fraction of the model and as well as the free motion of water molecules in the oil. These particles also increased the interaction between the oil and water molecules, indicating that insulating oil containing nano-particles has a greater binding effect on water. The diffusion coefficient of water in oil containing nano-SiO₂ particles was reduced, such that water molecules were less likely to diffuse. The results also show that these particles adsorb water molecules in the oil and to reduce diffusion. Consequently, the addition nano-scale SiO₂ particles could potentially improve the breakdown voltage of the insulating oil. Full article

(This article belongs to the Special Issue Molecular Dynamics in Nanomaterials and Nanofluids)

► Show Figures

Figure 1

14 pages, 6073 KiB

Open AccessArticle

Phase Transformation, Twinning, and Detwinning of NiTi Shape-Memory Alloy Subject to a Shock Wave Based on Molecular-Dynamics Simulation

by Man Wang, Shuyong Jiang and Yanqiu Zhang

Materials 2018, 11(11), 2334; https://doi.org/10.3390/ma11112334 - 21 Nov 2018

Cited by 30 | Viewed by 6858

Abstract

Martensitic transformation, reverse martensitic transformation, twinning, and detwinning of equiatomic nickel–titanium shape-memory alloy (NiTi SMA) under the action of a shock wave are studied using a molecular-dynamics simulation. In the loading process of a shock wave, B2 austenite is transformed into B19′ martensite, [...] Read more.

Martensitic transformation, reverse martensitic transformation, twinning, and detwinning of equiatomic nickel–titanium shape-memory alloy (NiTi SMA) under the action of a shock wave are studied using a molecular-dynamics simulation. In the loading process of a shock wave, B2 austenite is transformed into B19′ martensite, whereas in the unloading process of the shock wave, B19′ martensite is transformed into B2 austenite. With repeated loading and unloading of the shock wave, martensitic transformation occurs along with twinning, but reverse martensitic transformation appears along with detwinning. The mechanisms for the twinning and detwinning of NiTi SMA subjected to a shock wave are revealed in order to lay the theoretical foundation to investigate the shape-memory effect and superelasticity. Full article

(This article belongs to the Special Issue Molecular Dynamics in Nanomaterials and Nanofluids)

► Show Figures

Figure 1

12 pages, 4138 KiB

Open AccessArticle

Influence of Polymethylsilsesquioxane Content to the Thermal Stability of Meta-Aramid Fiber Insulation Paper

by Wei Zheng, Jufang Xie, Jingwen Zhang, Chao Tang and Zhongyong Zhao

Materials 2018, 11(11), 2317; https://doi.org/10.3390/ma11112317 - 19 Nov 2018

Cited by 11 | Viewed by 3419

Abstract

Polymethylsilsesquioxane (PMSQ) nanoparticles with mass percentages of 0, 2.5, 5.0, 7.2, 9.4 wt %, respectively, were constructed by molecular dynamics methods in this paper. Composite molecular models were established using PMSQ and MPIA (poly-metaphenylene isophthalamide) fiber. The influence of different PMSQ contents on [...] Read more.

Polymethylsilsesquioxane (PMSQ) nanoparticles with mass percentages of 0, 2.5, 5.0, 7.2, 9.4 wt %, respectively, were constructed by molecular dynamics methods in this paper. Composite molecular models were established using PMSQ and MPIA (poly-metaphenylene isophthalamide) fiber. The influence of different PMSQ contents on the thermal stability of meta-aramid insulation paper was analyzed from the parameters of mechanical property, interaction energy, and mean square displacement. The results showed that the trend of mechanical properties decreased with the increase of PMSQ content. When the PMSQ content was 2.5 wt %, the mechanical properties of the composited model were the best, which was about 24% higher than that of the unmodified model. From an intermolecular bonding and nonbonding point of view, the energy parameters of composite model with the 2.5 wt % content was better than those of the composite model with other contents. Therefore, it is considered that MPIA can interact better with the 2.5 wt % content PMSQ composite model. When the PMSQ content is 2.5 wt %, the overall chain movement in the composite model is slower than that of the unmodified model, which can effectively inhibit the diffusion movement of the MPIA chain. In general, the thermal stability of composite molecular models MPIA and PMSQ (2.5 wt %) was better improved. Full article

(This article belongs to the Special Issue Molecular Dynamics in Nanomaterials and Nanofluids)

► Show Figures

Figure 1

11 pages, 5157 KiB

Open AccessArticle

Atomistic Investigation on Diffusion Welding between Stainless Steel and Pure Ni Based on Molecular Dynamics Simulation

by Yanqiu Zhang and Shuyong Jiang

Materials 2018, 11(10), 1957; https://doi.org/10.3390/ma11101957 - 12 Oct 2018

Cited by 12 | Viewed by 3878

Abstract

Based on molecular dynamics (MD) simulation, the behaviors and mechanisms of diffusion welding between 304 stainless steel (304 SS) and pure Ni were investigated in the present study. The results show that surface roughness has a significant influence on the diffusion behaviors of [...] Read more.

Based on molecular dynamics (MD) simulation, the behaviors and mechanisms of diffusion welding between 304 stainless steel (304 SS) and pure Ni were investigated in the present study. The results show that surface roughness has a significant influence on the diffusion behaviors of atoms during diffusion welding between two different materials, and it is suggested that the rough surface should be set on the pure Ni rather than the 304 SS during the diffusion welding between them. Temperature plays an important role in the interface diffusion. With the increase of temperature, the number of atoms diffusing into the opposite side increases and the diffusion distances increase as well. As a consequence, the diffusion welding should be performed at a suitably elevated temperature. The influence of vertical pressure on the diffusion bonding between the two materials includes two aspects. One is to increase the contact area via deforming the asperities or grooves at the interface, which provides more opportunities for the diffusion between the two materials. The other is to reduce the mobility of atoms within a lattice. As a consequence, the pressure effect is smaller than temperature effect during diffusion welding between 304 SS and pure Ni. Full article

(This article belongs to the Special Issue Molecular Dynamics in Nanomaterials and Nanofluids)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Molecular Dynamics in Nanomaterials and Nanofluids

Share This Special Issue

Special Issue Editor

Special Issue Information

Keywords

Published Papers (9 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI