Abstract: HNBR is a widely used oil resistant polymer with good tear strength. Due to these properties, HNBR is used in oil wells. However, harsh working environments require high equipment maintenance fees and HNBR will be degraded when contacted with H2S. This study aims to improve the mechanical properties and H2S resistance of HNBR through molecular dynamics simulations. Some of the simulation results are compared with experimental results and literature values. In this study, the solubility parameters and densities of pure HNBR with varying acrylonitrile content, FKM and three surfactants (KBM503, a trimethoxysilane methacrylate, A10, a perfluoroalkoxy bis(alkylamide), and Capstone-62MA, a semifluorinated methacrylate) are calculated by molecular dynamics simulation. The cohesive energy densities of 50/50 HNBR/FKM blends with different kinds and content of surfactants are calculated. The diffusion of H2S and CO2 are predicted by molecular dynamics simulation. The solubility coefficients of H2S and CO2 are predicted by Grand Canonical Monte Carlo (GCMC) simulations. A series of NPT simulations (constant of number of atoms, pressure and temperature) are used to estimate the glass-transition temperature of Capstone-62MA grafted HNBR. Dissipative Particles Dynamics (DPD) simulations are used to obtain the micro phase separation of Capstone-62MA grafted HNBR. The results shows that the solubility parameter values and densities we obtained from molecular dynamics simulations are fitted very well with literature values. According to our calculation of energy of mixing for HNBR/FKM blends with three surfactant (KBM503, A10 and Capstone-62MA), KBM503 has the largest effect. Based on the experiment results for HNBR/FKM blends with different mass fractions of KBM503, the tensile stress at break and elongation at break increases with the increases of KBM503 content until the mass fraction KBM503 is equal to 5%. When the mass fraction of KBM503 is 5%, adding more KBM503 decreases both mechanical properties. However, the tear strength keeps increasing when the mass fraction of KBM503 increases. The conclusion obtained from these experiments and simulations indicates that mixing HNBR with FKM can improve some mechanical properties but this method has disadvantages due the large discrepancy between the solubility parameters of HNBR and FKM. Gas diffusion and solubility calculations indicate that the diffusion and solubility of H2S decrease with the content of Capstone-62MA increases. The gas diffusion of H2S also decreases with increasing content of acrylonitrile in HNBR. However, the solubility of H2S also increases with the content of acrylonitrile in HNBR. For comparison with H2S, the diffusivity and solubility of CO2 are calculated. The diffusion of CO2 increases with the increase of Capstone-62MA content. The solubility of CO2 decreases with increases of Capstone-62MA in HNBR with 17 wt% acrylonitrile content. For HNBR with 36 wt% acrylonitrile content, increasing the content of Capstone-62MA first increases the solubility of CO2 and then reduces it when the content of Capstone-62MA is larger than 2%. The calculation also indicates that diffusion and solubility coefficient are reduced when the content of acrylonitrile increases in HNBR. Calculations for the glass-transition temperature of HNBR with different numbers of Capstone-62MA chains suggest that the glass-transition temperature is not changed by grafting Capstone-62MA onto the backbone of HNBR. These results are compared with experimental results. Although the glass-transition temperatures obtained from simulations are higher than those obtained from experiment, they have the same trend as the content of Capstone-62MA is changed. DPD simulations suggest that micro phase separation exists in the Capstone-62MA grafted HNBR and this phenomenon improves the mechanical performance of polymers. In summary, we have used computer modeling to design new polymer materials and perform molecular dynamics simulations, Monte Carlo simulations and DPD simulations to predict some properties of these new materials. Some simulation results are compared with experimental results indicating that we indeed obtain a newly a polymer material with improved properties with the help of computer simulations.
Keywords: Computer simulation,Design, New polymers