Molecular Simulation Study on the Hydrogen Permeation Behavior and Mechanism of Common Polymers

This research aimed to provide an understanding of the selection and safe application of pipeline liner materials for hydrogen transport by examining the permeation properties and mechanisms of hydrogen within polymers commonly used for this purpose, such as high-density polyethylene (HDPE) and ethylene-vinyl alcohol copolymer (EVOH), through molecular simulation. The study was carried out within defined operational parameters of temperature (ranging from room temperature to 80 °C) and pressure (from 2.5 to 10 MPa) that are pertinent to hydrogen pipeline infrastructures. The results reveal that with an increase in temperature from 30 °C to 80 °C, the solubility, diffusion, and permeability coefficients of hydrogen in HDPE increase by 18.7%, 92.9%, and 129.0%, respectively. Similarly, in EVOH, these coefficients experience increments of 15.9%, 81.6%, and 112.7%. Conversely, pressure variations have a negligible effect on permeability in both polymers. HDPE exhibits significantly higher hydrogen permeability compared to EVOH. The unique chain segment configuration of EVOH leads to the formation of robust hydrogen bonds among the hydroxyl groups, thereby impeding the permeation of hydrogen. The process by which hydrogen is adsorbed in polymers involves aggregation at low potential energy levels. During diffusion, the hydrogen molecule primarily vibrates within a limited range, with intermittent occurrences of significant hole-to-hole transitions over larger distances. Hydrogen exhibits a stronger interaction with HDPE compared to EVOH, leading to a higher number of adsorption sites and increased hydrogen adsorption capacity in HDPE. Hydrogen molecules move more actively in HDPE than in EVOH, exhibiting greater hole amplitude and more holes in transition during the diffusion process.

Impact of biochar coexistence with polar/nonpolar microplastics on phenanthrene sorption in soil

Microplastics and biochar normally coexist in soil. In this study, two microplastics of different polarities (nonpolar polyethylene (PE) and polar polybutylene adipate-co-terephthalate (PBAT)) and two wheat straw biochars produced at 400 (W4) and 700 °C (W7) were selected to investigate the sorption behaviors of phenanthrene in soil where microplastics and biochar coexisted. The results showed that the presence of PE more significantly weakened the adhesion of soil particles onto biochar than the presence of PBAT. Meanwhile, the presence of biochar enhanced the soil particle attachment on the microplastic surface. As a result, the sorption behavior of phenanthrene was significantly different in soil where biochar coexisted with microplastics of different polarities. The K_oc values of PE-biochar-soil mixtures at C_e= 0.005 C_s were up to 42 % lower than those of PBAT-biochar-soil mixtures, which is related to lower micropore area of particles isolated from the former. However, at C_e = 0.05 C_s and 0.5 C_s, the K_oc values of PE-biochar-soil mixtures were up to 1.4 times higher than those of PBAT-biochar-soil mixtures because of a more significant reduction in biochar surface polarity when it coexisted with nonpolar PE.

Multiscale Strategy for Predicting Radiation Chemistry in Polymers

A primary mode for radiation damage in polymers arises from ballistic electrons that induce electronic excitations, yet subsequent chemical mechanisms are poorly understood. We develop a multiscale strategy to predict this chemistry starting from subatomic scattering calculations. Nonadiabatic molecular dynamics simulations sample initial bond-breaking events following the most likely excitations, which feed into semiempirical simulations that approach chemical equilibrium. Application to polyethylene reveals a mechanism explaining the low propensity to cross-link in crystalline samples.

Crystal structures, crystallization and II-I transition behaviors of iPB-1 in iPB-1/UHMWPE blends - Part 1. Crystal structures and crystallization behaviors

Isotactic polybutene-1 (iPB-1) is of particular commercial interest due to its excellent mechanical performances. The form I polymorph is preferred in most industrial applications, while the form II is kinetically...

Critical Thickness of Free-Standing Nanothin Films Made of Melted Polyethylene Chains via Molecular Dynamics

The mechanical stability of nanothin free-standing films made of melted polyethylene chains was predicted via molecular dynamics simulations in the range of 373.15-673.15 K. The predicted critical thickness, tc, increased with the square of the temperature, T, with additional chains needed as T increased. From T = 373.15 K up to the thermal limit of stability for polyethylene, tc values were in the range of nanothin thicknesses (3.42-5.63 nm), which approximately corresponds to 44-55 chains per 100 nm2. The density at the center of the layer and the interfacial properties studied (density profiles, interfacial thickness, and radius of gyration) showed independence from the film thickness at the same T. The polyethylene layer at its tc showed a lower melting T (<373.15 K) than bulk polyethylene.

Temperature dependence of the interfacial bonding characteristics of silica/styrene butadiene rubber composites: a molecular dynamics simulation study

Based on our previous studies on the modification of in-chain styrene butadiene rubber (SBR) using 3-mercaptopropionic acid as well as its composites filled with silica, we further constructed two types of models (amorphous and layered) to investigate the temperature dependence of the interfacial bonding characteristics of silica/SBR composites via molecular dynamics (MD) simulation. The competing effects of rubber–rubber interactions and filler–rubber interactions were identified, and the relationship between the competing effects and the temperature was determined. Besides this, the effect of temperature on the mobility and distribution of SBR chains on the surface of silica was investigated. It was found that the stronger the interfacial interactions, the less sensitive the motion of SBR chains to temperature. Finally, the number and length of hydrogen bonds as a function of temperature were analyzed. These simulated results deepened the understanding of interface temperature dependence of the silica/SBR composites and gave a molecular level explanation for the existence of an optimum modifier content (14.2 wt%) that is temperature independent.

Temperature dependence of the interface between silica and styrene butadiene rubber modified by 3-mercaptopropionic acid was investigated by molecular dynamics simulation.

Role of conformation in crystal formation and transition of polybutene-1

Polymer conformation is the molecular basis underlying essentially all physical properties of polymers, and chain conformation and conformational energy play central roles in crystalline structure formations and structure transitions of polymers.

Computational study on acetophenone in amorphous polyethylene

Polyethylene (PE) is widely used as an electrical insulating material. Acetophenone (AP) is a major residue in PE and is considered one of the causes of insulation deterioration. However, the physicochemical explanation of the influence of AP is still unknown. Therefore, in the present study, the behavior of AP molecules in amorphous PE was investigated using molecular dynamics (MD) simulations and quantum chemical calculation. First, the basic properties of the AP molecule were evaluated from the viewpoint of molecular electrostatic potential (MEP), molecular orbitals, and energy levels. Subsequently, an amorphous PE system containing AP molecules was studied using MD simulations. The results clearly indicate that AP does not greatly change the density and radius of gyration of amorphous PE. Quantum computations were performed using a part of the structure obtained from the MD simulations, suggesting that AP acts as a trap site in amorphous PE. It was also revealed that under the external electric field, the total density of state (DOS) changes with a dependence on the applied direction. Results of these calculations help in explaining previous experimental results.

Molecular dynamics simulation of effect of glycerol monostearate on amorphous polyethylene in the presence of water

Polyethylene (PE) is used widely as an electrical insulating material. However, the deterioration of its insulating ability is accelerated by exposure to a humid environment. To prevent the influence of water molecules, mixing 2,3-dihydroxypropyl octadecanoate-known as glycerol monostearate (GMS)-into PE has been proposed. However, the physical mechanism underlying the effect of GMS remains unclear. In the present study, the behavior of water molecules in amorphous PE with and without GMS molecule(s) was investigated in terms of diffusion and clustering using molecular dynamics (MD) simulations. Analyzing the mean square displacement (MSD), diffusion coefficient and radial distribution function (RDF) of the water molecules revealed that GMS contributed to suppressing the diffusion and dispersion of water molecules. Furthermore, it was demonstrated that, in the case of 4 wt% GMS and less than 2 wt% water, GMS contributes to reducing the diffusion coefficient of water molecules but does not change the glass transition temperature (T _g) of the system drastically.