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Nanocomposite of Fullerenes and Natural Rubbers: MARTINI Force Field Molecular Dynamics Simulations.

ABSTRACT: The mechanical properties of natural rubber (NR) composites depend on many factors, including the filler loading, filler size, filler dispersion, and filler-rubber interfacial interactions. Thus, NR composites with nano-sized fillers have attracted a great deal of attention for improving properties such as stiffness, chemical resistance, and high wear resistance. Here, a coarse-grained (CG) model based on the MARTINI force field version 2.1 has been developed and deployed for simulations of cis-1,4-polyisoprene (cis-PI). The model shows qualitative and quantitative agreement with the experiments and atomistic simulations. Interestingly, only a 0.5% difference with respect to the experimental result of the glass transition temperature (T_g) of the cis-PI in the melts was observed. In addition, the mechanical and thermodynamical properties of the cis-PI-fullerene(C₆₀) composites were investigated. Coarse-grained molecular dynamics (MD) simulations of cis-PI-C₆₀ composites with varying fullerene concentrations (0-32 parts per hundred of rubber; phr) were performed over 200 microseconds. The structural, mechanical, and thermal properties of the composites were determined. The density, bulk modulus, thermal expansion, heat capacity, and T_g of the NR composites were found to increase with increasing C₆₀ concentration. The presence of C₆₀ resulted in a slight increasing of the end-to-end distance and radius of the gyration of the cis-PI chains. The contribution of C₆₀ and cis-PI interfacial interactions led to an enhancement of the bulk moduli of the composites. This model should be helpful in the investigations and design of effective fillers of NR-C₆₀ composites for improving their properties.

SUBMITTER: Kitjanon J

PROVIDER: S-EPMC8626026 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:After the discovery of membrane-reversible electroporation decades ago, the procedure has been used extensively in biology, biotechnology and medicine. The research on the basic mechanism has increasingly attracted attention. Although most research has focused on models that consider all atomic and molecular interactions and much atomic-level information can be obtained, the huge computational demand limits the models to simulations of only a few nanometers on the spatial scale and a few nanoseconds on the time scale. In order to more comprehensively study the reversible electroporation mechanism of phospholipid membrane on the nanoscale and at longer time intervals of up to 100 ns, we developed a dipalmitoylphosphatidylcholine (DPPC) phospholipid membrane model with the coarse-grained Martini force field. The model was tested by separately examining the morphology of the phospholipid membrane, the hydrophilic channel size, the distribution of the voltage potential on both sides of the membrane, and the movement of water molecules and ions during electroporation. RESULTS:The results showed that the process went through several stages: (1) the formation of the pore with defects originating on the surface. (2) The maintenance of the pore. The defects expanded to large pores and the size remains unchanged for several nanoseconds. (3) Pore healing stage due to self-assembly. Phospholipid membrane shrunk and the pore size decreased until completely closed. The pores were not circular in cross-section for most of the time and the potential difference across the membrane decreased dramatically after the pores formed, with almost no restoration of membrane integrity even when the pores started to close. CONCLUSIONS:The mechanism of the reversible electroporation process on the nanoscale level, including defects, expansion, stability, and pore closing stages on a longer time scale of up to 100 ns was demonstrated more comprehensively with the coarse-grained Martini force field, which took both the necessary molecular information and the calculation efficiency into account.

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Nanocomposite of Fullerenes and Natural Rubbers: MARTINI Force Field Molecular Dynamics Simulations.

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