ABSTRACT
Molecular dynamics (MD) simulation, by employing the COMPASS force field, was utilized to investigate structural and thermal characteristics as well as interfacial interactions between components of nanocomposite consisting of poly(lactic acid) (PLA)/natural rubber (NR)/nanosilica, abbreviated as PSxN, where 1 ≤ x ≤ 7 and it represents the parts of SiO2 nanoparticles added to the PLA/NR (PN) blend. Analysis of the obtained results including density (ρ), fractional free volume (FFV), glass transition temperature (Tg), interaction energy (Einteraction), and radial distribution function (RDF) of these nanocomposites was performed. Comparing Einteraction of nanocomposites with that of the PN blend showed that the interactions between the chains of the two polymers are highly dependent on the added amounts of silica nanoparticles, so that by adding silica to the PN blend to obtain PS1N and PS3N nanocomposites, the amount of Einteraction was reduced to a smaller positive value, which indicates the tendency of the nanocomposite's components to interact with each other. By further addition of silica nanoparticles to have PS5N and PS7N nanocomposites and then by analysis of the RDF results, it was found that the nanoparticles were not well dispersed in these two nanocomposites and they were accumulated in the NR rubbery phase. Therefore, the percolation threshold for silica loading on the PN blend is at most 3 parts (x = 3). These results as well as the other obtained simulation results were compared with the available experimental data, and the agreement observed between them approved the simulation procedure and validated the obtained results.
ABSTRACT
Molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations were conducted to investigate the transport properties of carbon dioxide, methane, nitrogen, and oxygen through pure and mixed matrix membranes (MMMs) based on polymers of intrinsic microporosity (PIM-1). For this purpose, first, 0.5 to 3 wt% of pristine single-walled carbon nanotube (p-SWCNT) and multi-walled carbon nanotube (p-MWCNT) were embedded into the pure PIM-1, and then for better dispersion of CNT particles into the polymer matrix and to improve the performance of the resulting MMMs, polyethylene glycol (PEG) functionalized SWCNT and MWCNT (f-SWCNT and f-MWCNT, respectively) were loaded. The characterization of the obtained MMMs was carried out by using density, glass transition temperature, X-ray pattern, and fractional free volume calculations. Comparing the obtained results with the available reported experimental data, indicate the authenticity of the applied simulation approach. The simulation results exhibit that the pristine and PEG-functionalized CNT particles improve the transport properties such as diffusivity, solubility, and permeability of the PIM-1 membranes, without sacrificing their selectivity. Also, the MMMs incorporated with 2 wt% of the functionalized CNT particles indicate better performance for the CO2 separation from other gases. According to the calculated results, the highest permeability and diffusivity for CO2 are observed in the [PIM-1/f-SWCNT] MMM among the other membranes which represent that the loading of the f-SWCNTs can enhance the CO2 separation performance of PIM-1 more than other CNTs studied in this work.
ABSTRACT
Pure polysulfone (PSF) and its composites with chitosan (CST), hyaluronic acid (HA), conventional poly(amidoamine), and hydroxyl poly(amidoamine) dendrimers as the membranes for separation of the gases, methane, carbon dioxide, hydrogen sulfide, nitrogen, and oxygen have been studied by molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The transport properties (solubility, diffusivity, and permeability) of pure and gas mixtures in the membranes were calculated and the results of the simulations were compared with the available experimental data. The simulated structural properties of the pure and composite PSF membranes including occupied volume, free volume, surface area, fractional free volume (FFV), and radius of gyration (R g ) were evaluated and their effects on the separability of the gases by the membranes were analyzed and interpreted by the obtained results.
