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Li C.,China University of Petroleum - East China | Zhang T.,Petrolum Production Engineering Research Institute of Huabei Oilfield Company | Ji X.,China University of Petroleum - East China | Wang Z.,China University of Petroleum - East China | And 3 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2016

Molecular dynamics simulations were carried out to investigate the influence of cations (Ca2+/Mg2+) on the stability of the foam system stabilized by sodium dodecyl polyoxyethylene sulfonate (A12E2SO3). First, the structure of A12E2SO3 monolayer at the air/water interface was studied through analyzing the distribution of A12E2SO3 headgroups and the orientation of surfactant molecules. Results show that the addition of Mg2+ can increase the distance between A12E2SO3 headgroups, broaden the distribution thickness of A12E2SO3 headgroups along z axis, and improve the orientation of A12E2SO3 molecules, which favored the foam stability. On the contrary, the addition of Ca2+ in the foam system made surfactant molecules more aggregated, which was detrimental to the foam stability. Second, the interaction of surfactant molecules and cations was also studied through calculating their binding/dissociation energy and mobility. Results reveal that the binding tendency of the head-Ca2+ ion-pair was stronger than that of the head-Mg2+ ion-pair, which disturbed the foam stability. Third, we studied the hydration of surfactant headgroups and cations through calculating the number and the mobility of hydrated water molecules around headgroups. Results show that due to the extra hydration of cations in the foam system, especially for that with the addition of Mg2+, the number of water molecules around headgroups was increased and their mobility was restricted, which was beneficial to the foam stability. In addition, two forms of hydrogen bond bridging structures (O1⋯H2O⋯O2 and O2⋯H2O⋯Os) were observed for the first time in anionic surfactants. The location and the formation probability of these structures were found to be related to the gauche conformation of A12E2SO3 headgroup backbones. It was also found that hydrogen bond bridging structures can affect the foam stability. © 2015 Elsevier B.V. Source

Jing N.,Shandong University | Jing N.,China University of Petroleum - East China | Xue Q.,Shandong University | Xue Q.,China University of Petroleum - East China | And 6 more authors.
RSC Advances | Year: 2012

The effect of defects including vacancy and Stone-Wales (SW) defects on the Young's modulus of graphene sheets is investigated using molecular dynamic (MD) simulations. The simulations show that the presence of defects reduces the Young's modulus of graphene sheets and Young's modulus decreases with increasing degree of defects. In addition, the vacancy defects bring about a decrease in the Young's modulus, but their reconstruction is an important factor in stabilizing the modulus. Furthermore, we explore the Young's modulus of graphene with defects functionalized by hydrogen atoms and find that the hydrogenation of vacancy defects can increase the Young's modulus of the defective graphene but the hydrogenation of SW defects has the opposite effect. © 2012 The Royal Society of Chemistry. Source

Hu S.,China University of Petroleum - East China | Hu S.,Key Laboratory of New Energy Physics and Materials Science in Universities of Shandong | Guo A.,Sinopec | Geng Y.,China University of Petroleum - East China | And 3 more authors.
Materials Chemistry and Physics | Year: 2012

The effect of 2-oleyl-1-oleylamidoethyl imidazoline ammonium methylsulfate (ODD) and halide ions on corrosion inhibition of mild steel in HCl solution has been studied by experimental and molecular dynamics simulation methods. Synergistic effects were observed between ODD and the halides, and the inhibition efficiency was found to follow the trend ODD-Cl - < ODD-Br - < ODD-I -. In molecular dynamics simulation, the analysis of fractional free volume and diffusion coefficient showed that the synergistic effect increased in the order ODD-Cl - < ODD-Br - < ODD-I -. The molecular dynamics simulation analysis agreed with the experimental results. © 2012 Elsevier B.V. All rights reserved. Source

Li X.,China University of Petroleum - East China | Xue Q.,China University of Petroleum - East China | Xue Q.,Key Laboratory of New Energy Physics and Materials Science in Universities of Shandong | Liu Z.,China University of Petroleum - East China | And 3 more authors.
Journal of Physical Chemistry C | Year: 2014

C4H nanotube (C4HNT) which is a novel kind of hydrogenated carbon nanotubes (CNTs) has gradually attracted much attention due to its unique structure and potential applications. In this work, we systematically studied the mechanical properties of C4HNT using classical molecular dynamics and molecular mechanics simulations. It is found that C4HNT can bear much greater radial pressure than CNT. For example, the collapse pressure of (10, 0) C4HNT can reach 25 GPa, which is more than 4 times that of (10, 0) CNT (6 GPa). However, hydrogenation weakens the value of Young's modulus of CNT, and leads to the descent of axial strength of CNT. Besides, it is demonstrated that the collapse pressure of C4HNT decreases with increasing tube diameter while the Young's modulus of C4HNT is independent of tube diameter. And the tube number, chirality, length have no effect on the axial and radial mechanical properties of C4HNT. The results show that C4HNT has much better radial mechanical properties than CNT so that C4HNT may be an ideal filler to enhance the local mechanical support of nanocomposites. © 2014 American Chemical Society. Source

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