جستجوی مقالات مرتبط با کلیدواژه « شبیه سازی دینامیک مولکولی » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

The asphaltene molecules play a very important role in the crude oil for the exteraction of oil from oil reservoirs. Therefore, in this study, the aggregation and deposition of asphaltene N6 in aromatic solvents such as cyclohexane, benzene, toluene, chlorobenzene and bromobenzene were investigated by using molecular dynamics simulation at room temperature and pressure. In addition, physical properties such as density and solubility parameter for N6 asphaltene and pure solvents were calculated and compared with experimental data. There is a good agreement between the simulation results and experimental data. In addition, the behavior of asphaltene molecules was studied for pure and soluble in aromatic solvents conditions. The results show that the asphaltene molecules aggregate due to π-π bonds between the aromatic rings in the structure of them. Finally, the simulation results indicate that the asphaltene molecules are soluble in chlorobenzene better than other solvents, and also it is better than toluene solvent.

We conducted a set of molecular dynamics simulations, as the first comparative study of the adsorption behavior of liquid hydrocarbon (propane, n-hexane, n-heptane, n-decane)/acid gases/water molecules over {} calcite surface and {001} octahedral kaolinite surface in nano-confined slit. According to atomic z-density profiles, hydrocarbon molecules have higher tendency towards the {} calcite surface than the {001} octahedral kaolinite surface. In addition, water molecules showed the same tendency for stronger adsorption over calcite surface than kaolinite. In contrast, acid gas molecules showed higher tendency towards kaolinite surface than calcite surface. This behavior was spotted within nanometer-sized slit pores. The results also pointed to reduction in self-diffusion coefficient of molecules with strong adsorption over mineral surfaces in nano-confined environment. Existence of a water phase in the middle-region of slit was confirmed by the molecular dynamics simulations’ results.

Poly()ε-caprolactone) ()PCL) has been widely investigated for medical applications because of its good physicochemical properties; however hydrophobic nature of PCL has been a colossal obstacle toward achieving scaffolds which offer satisfactory cell attachment and proliferation. To date, different methods have been proposed to lower the hydrophobicity of PCL. Moreover, molecular dynamic simulation (MD) is an excellent method to predict and study the chemical and physical properties of polymeric systems. To this end, MD study was assigned to evaluate the PCL/Pluronic blend. Moreover, some experimental data on PCL/Pluronic blend were collected and compared with the simulated results. Thermodynamic properties of neat and blended PCL were also calculated using MD simulation. The blend of PCL/Pluronic possessed lower density and higher free volume in comparison with neat PCL because of high mobility and low glass transition temperature of Pluronic chains and due to good molecular interactions between polypropylene oxide blocks of Pluronic and PCL. The ratio of the bulk to shear modulus revealed a toughened PCL blended substrate in comparison to its pure form. Moreover, a high interaction energy between the PCL/Pluronic blend and water molecules was observed due to the thermodynamically favored interactions of polyethylene oxide blocks of Pluronic and water molecules. Mean square displacement of water molecules at the bulk and in the surface of water layer placed in the vicinity of neat and blended PCL was calculated. The results revealed a difference between the behavior of the bulk and interfacial water molecules. Water contact angle measurements were carried out in order to evaluate the simulation results and demonstrated a considerable improvement in hydrophilicity of the PCL thin layers when blended with Pluronic.

Understanding the mechanism underlying the behavior of polymer-based nanocomposites requires investigations at molecular level that challenge experimental techniques. Molecular dynamic (MD) simulation as one of the most commonly used computation methods is being increasingly partnered with experiments. In the present work، we study some properties of polymer-based nanocomposites including carbon nanotube، boron nitrides nanotube، functionalized carbon nanotube and several polymers and copolymers. Radial distribution function، diffusion and radius of gyration are some physical chemistry properties that have been calculated for different polymerbased nano composites using MD simulation. Also، the interface of nanotube-polymer of polymeric nanocomposites is studied. The intermolecular interaction energy between carbon nanotubes and polymer molecules is computed and the morphology of polymers physisorbed to the surface of nanotubes is investigated by the radius of gyration and the dihedral angle. Our results show that the intermolecular interaction in our systems is strongly influenced by the specific monomer structure of polymer. The high values of intermolecular interaction energy of such composites suggest to us that an efficient load transfer would exist in the interface between nanotube and conjugated polymer، which is of a key role in the composite reinforcement practical applications.

Dendrimers are a relatively new class of materials with unique molecular architectures and dimensions in comparison to linear polymers. Dendritic macromolecules containing several types of functional groups can be successfully synthesized through divergent or convergent method. The functional surface groups make them very hydrophilic and highly water soluble. Dendrimer diameters increase with generations in increments of up to 1 nm per generation، while molecular weight and number of functional surface groups increase exponentialy. An ideal dendritic drug-carrier must be non-toxic، non-immunogenic، and preferably biodegradable and present an adequate biodistribution. This review investigates recent advances in the application of drug-conjugated PAMAM dendrimers in drug delivery and finally، molecular dynamics simulations of PAMAM structures and their properties are discussed

Investigation and optimization of polymeric nanocomposite properties including gas diffusion and barrier properties requires characterization study at the molecular level. Experimental methods at this scale are time consuming, expensive and in most cases associated with many experimental errors. Simulation approaches including molecular dynamics simulation (MDS) are very appropriate, fast and low expense alternatives for this purpose to study the properties at nanometric length scale. In this article, the structures of polymer-filled nanocomposites are described at molecular level, and the principles of MDS are introduced. Then, the literature is surveyed in the field of MD simulation of gas diffusion through polymer systems and their barrier properties. The softwares used for the study in this area is also introduced, classified and compared. The trend of the number of published papers during the last decade on this subject are finally described and discussed.

Present work aims at investigating rheological behavior of linear hydrocarbons by means of non-equilibrium molecular dynamics (NEMD) simulation. Simulation set up was a flow of hydrocarbon molecules confined between two molecular parallel plates. Through moving the top wall at constant velocity and investigation of relation of viscosity to shear stress, rheological behavior of hydrocarbons could be found out. Viscosity of hydrocarbons has been calculated by means of integration of Newtonian equations of motion and then shear stress tensor calculation and division of calculated shear stress by exerted shear rate. Our code verified with experimental data for light hydrocarbons (methane, ethane, propane and n-butane), reported results for a long chain hydrocarbon (C100H202), and results presented for some other hydrocarbons. According to the obtained results, it was found that with increasing hydrocarbon chain length, fluid viscosity will increase. Furthermore, the simulation results reveal that long chain hydrocarbons have a shear thinning non-Newtonian behavior with a power law relation.

Molecular Dynamic Simulation is a simple tool to investigate the molecular properties of the nanoscale systems. One of the most popular systems that is widely considered is Carbon Nano Tubes CNT immersed in water. In this research, NVT & NPT simulations are applied to study water molecule collections within CNT's as well as the effect of pressure on them. Results showed that water molecules can not enter CNT's of less than 6.78 Angestrom diameter. Also the current work confirmed the positive effect of pressure on water molecule's collection within CNTs.