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1

Isomorph Scaling of Hard Sphere and Lennard-Jones Fluids

Heyes David M., Pieprzyk Sławomir, Brańka Arkadiusz C.

Computational Methods in Science and Technology

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2023

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Vol. 29, No. 1-4

45--55

EN

The transport coefficients of model monatomic fluids are explored within the context of isomorph theory. An extension of our previous study in this field to the thermal conductivity of Lennard-Jones (LJ) fluids is reported here. The relationship to and comparisons with the behavior of the LJ system and those of hard spheres (HS), which form perfect isomorphs at all densities are made. The HS and LJ transport coefficients obtained by MD simulations when scaled by socalled macroscopic (‘isomorph’) units, and the density is scaled by the freezing density, form curves which are extremely similar, and in near quantitative agreement apart from close to freezing in most cases. It is shown that to a large extent the excellent ‘isomorph’ scaling of the transport coefficients exhibited by the LJ system, even at low densities, can be traced back to the dominance of the repulsive part of this potential for these dynamical quantities, which can reasonably accurately be accounted for by the scaling behavior of hard spheres. Numerical support for this conclusion using molecular dynamics data for the HS and LJ model fluids is presented.

2

Morphological analysis of organo-montmorillonites via MD simulations

Karataş Deniz, Tekin Adem, Can Muhammed F., Xu Zhenghe, Çelik Mehmet S.

Physicochemical Problems of Mineral Processing

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2022

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Vol. 58, iss. 5

art. no. 152499

EN

Adsorption on clay surfaces has been studied intensively in recent years. The most curious subject of these studies, which are generally experimental, is how the surfactants are adsorbed at the atomic level to the surface. In this study, the adsorption of quaternary amine salt (tetradecyl dimethyl ethyl benzyl ammonium chloride–TDEBAC) to sodium montmorillonite (Na-MMT) with various cation exchange capacities (CEC) was investigated by using Molecular Dynamics (MD) simulation. In the simulations, as in the experimental studies, it was revealed that the surfactants were both adsorbed on to basal surfaces and settled between the layers. From the morphological analysis obtained from MD simulations, it was calculated that the inter-molecular interaction between the layers was higher than on the basal surface. For example, for the model with 118 CEC motif, the binding energy of all three surfactants in the models with the hydrophilic heads facing the same direction was calculated as -678.18 kcal/mol at the basal surface, while this value was found to be -688.90 kcal/mol in the interlayer. The more striking result is that in the simulations made by turning the head of the middle one of the three surfactants towards the tails of the right and left ones, only -34.86 kcal/mol binding energy was calculated on the basal surface, while this value was -525.63 kcal/mol in the interlayer. As compared middle reversed surfactant models with the same direction ones, despite increased CEC the intermolecular interaction decreased for the basal surface, but the interaction increased between the layers.

3

Effect of the oxygen-containing functional group on the adsorption of hydrocarbon oily collectors on coal surfaces

Wan He, Hu Xianglin, Luukkanen Saija, Qu Juanping, Zhang Chonghui, Xue Jiwei, Li Hui, Yang Wei, Yang Shenghong, Bu Xianzhong

Physicochemical Problems of Mineral Processing

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2022

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Vol. 58, iss. 4

art. no. 149937

EN

The oxygen-containing functional groups (OCFG) on the coal surface affect the adsorption effect of hydrocarbon oily collectors (HOC). An investigation of the interaction between the HOC and OCFG in the absence and presence of water is conducive to understanding the effect of OCFG type on the adsorption of HOC on the coal surface. In this paper, FTIR analysis was used to analyze the OCFG type of coal surface. The adsorption behavior of HOC on different OCFG surfaces was investigated using molecular dynamics simulation. The results indicated the presence of OCFG such as -OH, -COOH, -C=O, and -COCH3 on the coal surface. In conditions without water, the effect of OCFG on HOC adsorption capability follows the order -COOH > -C=O > -OH > -COCH3. In an aqueous solution, the effect of OCFG on HOC adsorption capability follows the order -C=O>-COCH3>-OH>-COOH. Moreover, the hydrophilicity of OCFG is the key factor that affects the adsorption effect of HOC. In other words, the adsorption effect of HOC on the coal surface in an aqueous solution does not depend on the strength of the interaction between the OCFG and HOC in the absence of water, but on the hydrophilicity of the OCFG. The -COOH and -OH on the coal surface are not conducive to the adsorption of HOC onto the coal surface. Masking the -COOH and -OH of the coal surface is beneficial in improving the coal flotation performance with HOC as a collector.

4

Molecular dynamics study of the fracture of single layer buckled silicon monosulfide and germanium selenide

Le M.-Q

Archives of Mechanics

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2022

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Vol. 74, nr 1

3--12

EN

Molecular dynamics simulations were conducted with the Stillinger–Weber potential at room temperature to study the mechanical properties and find the mode-I critical stress intensity factor of buckled two-dimensional (2D) hexagonal silicon mono-sulfide (SiS) and germanium selenide (GeSe) sheets. Uniaxial tensile tests were simulated for pristine and pre-cracked sheets. 2D Young’s modulus of SiS and GeSe are estimated at 38.3 and 26.0 N/m, respectively. Their 2D fracture strength is about 3.1–3.5 N/m. By using the initial crack length with the corresponding fracture stress, their mode-I critical stress intensity factor is estimated in the range from 0.19 through 0.22 MPapm. These values differ within 5% from those obtained by the surface energy and are very small compared to the reported fracture toughness of single-crystalline monolayer graphene.

5

Effect of Nanoindentation Rate on Plastic Deformation in Cu Thin Films

Chocyk Dariusz, Zientarski Tomasz

Advances in Science and Technology. Research Journal

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2022

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Vol. 16, no 1

170--179

EN

The paper investigates the nanoindentation process with different rates in the Cu (001) of FCC system. The indentation process was done using molecular dynamics simulation based on the embedded atom method theory and Morse potential. Simulation process of indentation used a rigid spherical indenter with the diamond structure. To structure characterization we applied the adaptive common neighbour and the dislocation extraction analysis. It was found that the range of the linear change of the indentation force depends on the rate of response of the system. The initial range of the linear dependence of stress evolution also depends on the rate of indentation. Moreover, the average total normal stress in the system is only compressive. After linear changes, we observe oscillating changes in stress evolution. During indentation, for the range of linear changes of stress, dislocations aggregated only around the indenter surface. The creation of dislocations is directly connected with the structural changes. The structure analysis revealed the formation of HCP and BCC structure in the Cu (001) of FCC systems and a correlation with the creation of dislocations.

6

Influence of Temperature on the Properties of Cellulose Iβ based on Molecular Dynamics Simulations

Huang Shuang, Wu Xin, Li Peixing

Fibres & Textiles in Eastern Europe

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2021

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Vol. 29, no. 6 (150)

32--36

EN

Natural plants, such as cotton and linen, are rich in cellulose Iβ. The properties of cellulose Iβ under different temperatures was studied using molecular dynamics simulations. Firstly, the crystal of cellulose Iβ was built. To verify the model, the X-ray fibre diffraction and thermal expansion coefficients were calculated, which were found to agree with experimental results. Then the Mulliken population of the bonds were computed and the movement of the centre chain and hydrogen bonds studied over the range 300-550 K using a PCFF force field. The results of the Mulliken population reveal the three steps of pyrolysis. The higher the temperature is, the more intensely the movement of the centre chain is. However, the impact of temperature on the movement of the centre chain is not obvious. From 300 K to 550 K, the total number of hydrogen bonds decreased by only 20%. Moreocer, the rupture of intrachain hydrogen bonds and the formation of interchain hydrogen bonds at 400 K~450 K temperature occurred.

7

Effect of rubber particles on impact resistance of concrete at a temperature of - 20 ℃

Yu Yong, Jin Zuquan, Zhu Han, Song Huamiao

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

383--396

EN

Studies have shown that rubberised concrete is a potential pavement material. Pavement materials are generally expected to possess concrete with high impact resistance, especially in regions where winter temperatures remain lower than the freezing point for long periods. However, knowledge about the performance of rubberised concrete on impact under low temperatures is still limited. In this study, experiments were conducted to evaluate the compressive strength, elasticity modulus, bending strength, and impact resistance of rubberised concrete at room temperature (20 °C) and at a sub-zero temperature (− 20 °C). Meanwhile, a new U-shaped specimen drop-weight test was performed as an impact test. The results indicated that although the impact toughness of both rubberised and plain concrete types decreased at low temperatures, rubber particles also had positive effects on concrete impact resistance at − 20 °C. In addition to macroscopic tests, mercury injection and molecular dynamics simulations were performed to understand the mechanism through which rubber particles improve the impact resistance of concrete at low temperatures. The pores that could not freeze accounted for 1.55% of the total pores in plain concrete; this value was 2.36% in concrete with a rubber particle density of 50 kg/m3. From the results of this study, we can conclude that the addition of rubber can change the distribution of water or ice in concrete pores, which leads to an improvement in the toughness of concrete at a low temperature (- 20 °C).

8

Flotation and molecular dynamics simulation of muscovite with mixed anionic/cationic collectors

Bai Yang, Li Caixia, An Hongyun, Wang Guoliang, Zhao Xin, Zhang Jinqi

Physicochemical Problems of Mineral Processing

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2020

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Vol. 56, iss. 2

313--324

EN

In this study, three kinds of anionic collectors (sodium oleate (NaOl), sodium dodecyl sulfonate (SDS) and naphthenic acid (NA)) were used in combination with dodecylamine (DDA) to investigate the flotation behavior of muscovite under the action of different mixed anionic/cationic collectors, and their mechanisms for adsorption on the muscovite (001) Surface were clarified using molecular dynamics simulations. The flotation results indicated that different mixed anionic/cationic collectors could improve the recovery of muscovite to varying degrees, but the optimum molar ratio of anionic collectors to DDA and the optimum mixed collector dosage were different. Molecular dynamics simulations showed that the mixed anionic/cationic collectors could significantly increase the hydrophobicity of the muscovite, as evidenced by the decrease in the calculated water molecule density on the muscovite surface and the diffusion coefficient of water molecules at the solid/liquid interface. The interaction between the amino group and the polar group of anionic collectors reduced the electrostatic repulsion between DDA cations and theoretically increased the adsorption capacity of the mixed anionic/cationic collectors on the muscovite surface. Moreover, DDA/NA and DDA/NaOl could improve the calculated carbon atom density on the muscovite surface, which enhanced the hydrophobic association between nonpolar carbon chains, thus further achieving an enhanced flotation performance.

9

Analysis of elastic deformation of amorphous polyethylene in uniaxial tensile test by using molecular dynamics simulation

Le Tien-Thinh

Computer Methods in Materials Science

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2020

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Vol. 20, No. 2

38--44

EN

In this paper, the linear elastic response to uniaxial tension of amorphous polyethylene was investigated by using Molecular Dynamics (MD) simulation. The polymeric system was initiated using a Monte Carlo-based technique and then equilibrated by a relaxation sequence at temperature of 100 K under a NPT control. Uniaxial tension test was carried out by modifying the corresponding component of the pressure tensor, with a loading rate of 0.5 bar/ps. The results showed that at 100 K (which is smaller than the glass transition temperature), the amorphous polymeric material exhibited a linear elastic response to uniaxial tension. The obtained Young’s modulus and Poisson’s ratio were also compared with values reported in the literature. Finally, parametric studies were performed on the stress-strain curve as a function of loading axis, number of chains and number of monomer units, respectively.

PL

W pracy przeprowadzono badania metodą dynamiki molekularnej sprężystej odpowiedzi amorficznego polietylenu w osiowosymetrycznej próbie rozciągania. System polimetryczny został zainicjowany metodą Monte Carlo a następnie zrównoważony poprzez relaksację w temperaturze 100 K ze sterowaniem NPT. Próby rozciągania przeprowadzono poprzez zmodyfikowanie odpowiedniej składowej tensora naprężeń, przyjmując prędkość obciążania 0.5 bar/ps. Wyniki wykazały, że w temperaturze 100 K (która jest niższa od temperatury zeszklenia), amorficzny polimer wykazuje liniową sprężystość w próbie rozciągania. Wyznaczone wartości modułu Younga i współczynnika Poissona zostały porównane z danymi literaturowymi. Wreszcie przeprowadzono parametryczną ocenę krzywych naprężenieodkształcenie w zależności od kierunku obciążenia, liczby łańcuchów oraz liczby jednostek monomeru.

10

Application of the Lennard-Jones potential in modelling robot motion

Wójcicki Piotr, Zientarski Tomasz

Informatyka, Automatyka, Pomiary w Gospodarce i Ochronie Środowiska

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2019

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T. 9, nr 4

14--17

EN

The article proposes a method of controlling the movement of a group of robots with a model used to describe the interatomic interactions. Molecular dynamics simulations were carried out in a system consisting of a moving groups of robots and fixed obstacles. Both the obstacles and the group of robots consisted of uniform spherical objects. Interactions between the objects are described using the Lennard-Jones potential. During the simulation, an ordered group of robots was released at a constant initial velocity towards the obstacles. The objects’ mutual behaviour was modelled only by changing the value of the interaction strength of the potential. The computer simulations showed that it is possible to find the optimal value of the potential impact parameters that enable the implementation of the assumed robotic behaviour scenarios. Three possible variants of behaviour were obtained: stopping, dispersing and avoiding an obstacle by a group of robots.

PL

W artykule zaproponowano metodę kontrolowania ruchu grupy robotów za pomocą modelu stosowanego do opisu oddziaływań międzyatomowych. Przeprowadzono symulacje metodą dynamiki molekularnej w układzie składającym się z ruchomych grup robotów oraz nieruchomych przeszkód. Zarówno przeszkody, jak i roboty składały się z jednolitych sferycznych obiektów. Oddziaływania między obiektami opisano za pomocą potencjału Lennard-Jonesa. Podczas symulacji, początkowo uporządkowana grupa robotów poruszała się ze stałą prędkością w kierunku przeszkód. Wzajemne zachowanie obiektów modelowano tylko poprzez zmianę wartości parametrów potencjału oddziaływań. Symulacje komputerowe wykazały, że możliwe jest znalezienie optymalnych wartości parametrów oddziaływania, które umożliwiają uzyskanie pożądanego zachowania robotów. W trakcie symulacji uzyskano trzy możliwe warianty zachowania: zatrzymywanie, rozpraszanie i omijanie przeszkód przez grupę robotów.

11

The cavitation nuclei transient characteristics of Lennard-Jones fluid in cavitation inception

Fu Q., Zhang B., Zhao Y., Zhu R., Liu G., Li M.

Polish Maritime Research

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2018

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S 2

75--84

EN

In the field of ocean engineering, cavitation is widespread, for the study of cavitation nuclei transient characteristics in cavitation inception, we applied theoretical analysis and molecular dynamics (MD) simulation to study Lennard-Jones (L-J) fluid with different initial cavitation nuclei under the NVT-constant ensemble in this manuscript. The results showed that in cavitation inception, due to the decrease of liquid local pressure, the liquid molecules would enter the cavitation nuclei, which contributed to the growth of cavitation nuclei. By using molecular potential energy, it was found that the molecular potential energy was higher in cavitation nuclei part, while the liquid molecular potential energy changes greatly at the beginning of the cavitation nuclei growth. The density of the liquid and the surface layer changes more obvious, but density of vapor in the bubble changes inconspicuously. With the growth of cavitation nuclei, the RDF peak intensity increased, the peak width narrowed and the first valley moved inner. When cavitation nuclei initial size reduced, the peak intensity reduced, the corresponding rbin increased. With the decrease of the initial cavitation nuclei, the system pressure and total energy achieved a balance longer, and correspondingly, they were smaller. In addition, at the beginning of the cavitation nuclei growth, the total energy and system pressure changed greatly.

12

Water film structure during rupture as revealed by MDS image analysis

Truong N. T., Dang L. X., Lin C.-L., Wang X., Miller J. D.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 4

1060--1069

EN

The structure of thin water films during the rupture process was investigated by a new approach, which combines molecular dynamics simulation (MDS) with image processing analysis. The analysis procedure was developed to convert MDS trajectories to readable 3D images. The water films were studied at different thicknesses by MDS to determine the critical thickness at which the film ruptures. The potential energy of each specific film thickness during the simulation time was analyzed, and the results showed that the potential energy of stable films remained unchanged while the potential energy kept decreasing for films which ruptured during the simulation time. By applying the new procedure, the molecular porosity, which is defined as the void fraction between the volume of molecular pores in the water film and the total volume of the water film, was calculated. The results of molecular porosity for different film thicknesses during the simulation time suggested a critical molecular porosity as 49%. In other words, stable films have a molecular porosity of less than 49%. If a water film has a molecular porosity greater than 49%, rupture occurs during the simulation.

13

Effect of oxidation on the wetting of coal surfaces by water: experimental and molecular dynamics simulation studies

Li E., Lu Y., Cheng F., Wang X., Miller J. D.

Physicochemical Problems of Mineral Processing

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2018

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Vol. 54, iss. 4

1039--1051

EN

The wettability of coal surfaces by water continues to be one of the key factors which determines the success of coal flotation. Consequently, oxidation of coal surfaces is a fundamental issue of interest. In this work, the effect of oxidation on the wetting of coal surfaces and the interaction between water molecules and oxygen-containing sites at the coal surface was investigated based on advancing/receding contact angle measurements and molecular dynamics simulations. For the simulation studies, a flat coal surface was constructed with the assistance of the molecular repulsion between graphite surfaces and the assembly of Wiser coal molecules. Our results indicated that the simulated advancing and receding contact angles were very similar, and both of them decreased, as expected, with an increase of hydroxyl sites at the coal surface. The good agreement between the simulated advancing/receding contact angles and the experimental receding contact angle values suggested that the configuration of the systems and the set of parameters for the simulation were appropriate. The spreading of water is mainly due to the hydrogen bonds formed between the interfacial water molecules and the hydroxyl sites at the coal surface. The hydroxyl groups show stronger hydration capacity than other oxygen-containing groups according to the calculated hydrogen bonds and interaction energies.

14

Synthesis, characterization and molecular dynamics simulation of dendronized poly(3,5-diphthalimidoalkylphenyl methacrylate)s

Alvarado N., Alegría L., Sandoval C., Gargallo L., Leiva A., Radic D.

Polimery

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2016

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T. 61, nr 1

10--15

EN

Dendronized methacrylates containing 3,5-diphthalimidoalkylphenyl moieties (with ethyl, propyl or butyl spacer groups) were synthesized. These monomers were then polymerized using radical polymerization. Monomers and polymers were characterized using Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance methods (1H NMR and 13C NMR). Molecular weight was estimated by multi-angle static light scattering (MALS). Molecular dynamics simulation was performed to evaluate the conformational radius of gyration (Rg) and the end-to-end distance (ree). Different spatial arrangements depending on the length of the spacer group are observed.

PL

Zsyntezowano dendrymeryczne metakrylany zawierające ugrupowania 3,5-diftalimidoalkilofenylowe (z etylowymi, propylowymi lub butylowymi grupami dystansującymi), a następnie monomery te poddano polimeryzacji rodnikowej. Do określenia struktury wyjściowych monomerów oraz otrzymanych polimerów zastosowano spektroskopię w podczerwieni z transformacją Fouriera (FT-IR) i metody magnetycznego rezonansu jądrowego (1H NMR i 13C NMR). Oznaczono również masę cząsteczkową polimerów metodą wielokątowego rozpraszania światła (MALS). Symulacje metodą dynamiki molekularnej pozwoliły na wyznaczenie konformacyjnych promieni bezwładności (Rg), a także odległości między końcami łańcucha (ree). Zaobserwowano różne układy przestrzenne, których rodzaj zależał od wielkości grupy dystansującej.

15

Molecular Dynamics Simulation Studies of the CL-20/DNB Co-crystal

Sun T., Xiao J. J., Ji G. F., Zhao F., Xiao H. M.

Central European Journal of Energetic Materials

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2016

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Vol. 13, no. 3

677--693

EN

Molecular dynamics (MD) simulation was conducted for a DNB (1,3-dinitrobenzene) crystal, a ε-CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) crystal, a CL-20/DNB co-crystal and a CL-20/DNB composite. From the calculated maximum bond length (Lmax) of the N−NO2 trigger bond, the cohesive energy density (CED) and the binding energy (Ebind), it was found that the CL-20/DNB co-crystal is more insensitive than its composite. Its thermal stability is also better than that of its composite. The pair correlation function (PCF) analysis method was applied to investigate the interfaces between different molecular layers in the CL-20/DNB co-crystal, and in the composite. Additionally, the calculated mechanical data showed that the moduli of the CL-20/DNB co-crystal and its composite are smaller and their elastic elongation and ductility are better than those of the ε-CL-20 and DNB crystals.

16

The interaction of poly(L-lactic acid) and the nucleating agent N,N'-bis(benzoyl) suberic acid dihydrazide

Cai Y.-H., Zhao L.-S.

Polimery

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2015

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T. 60, nr 11-12

693--699

EN

Since N,N'-bis(benzoyl) suberic acid dihydrazide [NA(S)] acts as a powerful nucleating agent for poly(L-lactic acid) (PLLA), it is necessary to study the nucleation mechanism of NA(S) in the crystallization of PLLA. The interaction between PLLA and NA(S) was investigated by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and temperature-dependent Raman spectroscopy. The results from FT-IR and temperature-dependent Raman spectroscopy showed that a hydrogen bond between the C=O of PLLA and the N-H of NA(S) was formed. The TGA also indicated the existence of an intense interaction between PLLA and NA(S), resulting in the potent nucleation ability of NA(S) for PLLA. Molecular dynamics simulations (MDS) were employed to simulate the interaction of PLLA on the NA(S) surface. The simulation results further confirmed the hydrogen bond between PLLA and NA(S). The MDS study also analyzed the interaction energy between PLLA and NA(S). The MDS results can be used to select the proper nucleating agents and design novel organic nucleating agents.

PL

Zbadano mechanizm zarodkowania przy użyciu N,N'-bis(benzoilo)dihydrazydu kwasu suberynowego [NA(S)] w procesie krystalizacji poli(kwasu L-mlekowego) (PLLA). Interakcje między cząsteczkami PLLA i NA(S) oceniano na podstawie spektroskopii w podczerwieni z transformacją Fouriera, analizy termograwimetrycznej oraz widm Ramana, rejestrowanych w różnej temperaturze. Stwierdzono, że pomiędzy tlenem z grupy C=O w łańcuchu PLLA a wodorem z grupy N-H obecnej w NA(S) tworzą się wiązania wodorowe. Analiza TGA wykazała, że ww. intensywne interakcje są wynikiem dużej zdolności NA(S) do zarodkowania krystalizacji PLLA. Do zbadania oddziaływań na powierzchni NA(S) zastosowano także symulacje metodą dynamiki molekularnej (MDS), które potwierdziły występowanie wiązań wodorowych PLLA/NA(S). Metodą MDS określono też energię interakcji (technika MDS może być wykorzystana przy wyborze środka zarodkującego odpowiedniego dla danego układu).

17

The Lennard-Jones Fluid in the Liquid-Vapour Critical Region

Heyes D. M.

Computational Methods in Science and Technology

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2015

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Vol. 21, No. 4

169--179

EN

The equation of state of the Lennard-Jones (LJ) fluid in the liquid-vapour (LV) critical region is investigated by Molecular Dynamics simulation (MD). The calculated pressure (P) and chemical potential (μ) are, within the simulation statistics, flat at the critical temperature between LJ reduced densities of ca. 0:26 to 0:34. The critical temperature, Tc, determined for an isotherm where (∂P/∂)T = 0 and (∂μ/∂ρ)T = 0, is shown to decrease with increasing system size and pure LJ potential interaction range, rc, using a tapering function going to zero beyond rc. The value of Tc obtained by extrapolating the system size and rc to ∞ is 1:316 ± 0:001, which is statistically within the uncertainties of previous literature values. The percolation threshold separation, rp, along the critical isotherm decreases monotonically with increasing density, ρ, and is for intermediate densities lower than that of the nearest equivalent hard-sphere system. The lines of constant percolation distance on the density-temperature projection of the phase diagram reveal a difference in qualitative behaviour, indicative of underlying structural differences on either side of the critical envelope. The mean square force in the critical region near to Tc is linear in ρ. Probability distributions of the nearest neighbour distance, absolute particle force and potential energy per molecule are presented.

18

Thermal Expansion of Explosive Molecular Crystals: Anisotropy and Molecular Stacking

Qian W., Zhang C., Xiong Y., Zong H., Zhang W., Shu Y.

Central European Journal of Energetic Materials

|

2014

|

Vol. 11, no. 1

59--81

EN

Molecular dynamics simulations of three typical explosive crystals, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 1,1-diamino-2,2- dinitroethene (FOX-7) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), were carried out under NPT ensemble and selected force field. The equilibrium structures at elevated temperatures were obtained, which show that the stacking behaviour of the molecules does not change with temperature. The coefficient of thermal expansion (CTE) values were calculated by linear fitting methods, and the results show that the CTE values are close to the experimental results and are anisotropic. The total energies of the cells expanding along each single crystallographic axis were calculated by the periodic density functional theory method, indicating that the energy change rates are anisotropic, and correlation equations of the energy change vs. CTE values were established. The essence of the anisotropy of the explosive crystal’s thermal expansion was compared and elucidated.

19

Modelowanie adsorpcji związków biologicznie czynnych na materiałach węglowych

Gauden P. A., Terzyk A. P., Furmaniak S., Wiśniewski M., Bielicka A., Werengowska-Ciećwierz K, Zieliński W., Kruszka B., Bieniek A.

Inżynieria i Ochrona Środowiska

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2013

|

T. 16, nr 2

225--234

PL

Omówiono wpływ porowatości oraz chemicznej natury powierzchni węgla aktywnego na adsorpcję trzech związków organicznych (benzenu, fenolu oraz paracetamolu) z rozcieńczonych roztworów wodnych w oparciu o obliczenia dynamiki molekularnej (pakiet GROMACS). Wykorzystano model porów szczelinopodobnych oraz model tzw. „miękkiego” węgla aktywnego. Charakteryzują się one stopniową zmianą struktury mikroporowatej. Ponadto w strukturę materiałów węglowych wbudowano różną ilość grup funkcyjnych. Wyniki otrzymanych symulacji komputerowych wykazują jakościową zgodność z pomiarami eksperymentalnymi. I tak na przykład zaobserwowano spadek adsorpcji dla paracetamolu w porównaniu z adsorpcją benzenu. Ponadto wyniki obliczeń komputerowych wskazują, że na proces adsorpcji związków organicznych mają wpływ zarówno porowatość, jak i chemiczna natura materiału węglowego (zawartość tlenu). Ten drugi z czynników decyduje o mechanizmie blokowania porów i związany jest ze zwiększeniem gęstości wody w pobliżu grup chemicznych (tworzenie klastrów). Efekt blokowania porów zależy także od rozmiaru porów i przestaje odgrywać rolę dla porów o szerokościach większych niż 0,68 nm. W konsekwencji cząsteczki adsorbowanych związków organicznych nie mogą wnikać w głąb struktury materiału węglowego, ale adsorbują się na powierzchni zewnętrznej porów w pobliżu ich wejść.

EN

MD simulation studies (GROMACS package) showing the influence of porosity and carbon surface oxidation on adsorption of three organic compounds (i.e. benzene, phenol, and paracetamol) from aqueous solutions on carbons were reported. Based on a model of slit-like pores and “soft” activated carbons different adsorbents with gradually changed microporosity were created. Next, different amount of surface oxygen groups was introduced. We observe quantitative agreement between simulation and experiment, i.e. the decrease in adsorption from benzene down to paracetamol. Simulation results clearly demonstrate that the balance between porosity and carbon surface chemical composition in organics adsorption on carbons, and the pore blocking determine adsorption properties of carbons. Pore blocking effect decreases with diameter of slits and practically vanishes for widths larger than c.a. 0.68 nm. Moreover, adsorbed molecules occupy the external surface of the slit pores (the entrances) in the case of oxidized adsorbents.

20

Zinc ion adsorption on carbon nanotubes in an aqueous solution

Ansari A., Mehrabian M. A., Hashemipour H.

Polish Journal of Chemical Technology

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2012

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Vol. 14, nr 3

29-37

EN

The literature devoted to numerical investigation of adsorption of heavy metal ions on carbon nanotubes is scarce. In this paper molecular dynamics is used to simulate the adsorption process and to investigate the effect of the infl uencing parameters on the rate of adsorption. The predictions of the molecular dynamics simulation show that the adsorption process is improved with increasing the temperature, pH of solution, the mass of nanotubes, and surface modifi cation of CNT using hydroxyl and carboxyl functional groups. The results predicted by the model are compared with the experimental results available in the literature; the close agreement validates the accuracy of the predictions. This study reveals that the water layers around the carbon nanotubes and the interaction energies play important roles in the adsorption process. The study also shows that electrostatic force controls the attraction of zinc ions on the nanotube sidewall.