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 (Tg) 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 Tg 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.
Highlights
Natural rubber (NR), mainly consisting of cis-1,4polyisoprene with high elasticity, is acknowledged to be virtually irreplaceable in applications such as tires and seals
The carbon black (CB) concentration has a significant influence on the rubber composite properties; e.g., increasing the amount of CB has been shown to lead to enhanced tear strength, tensile strength, and elastic modulus [21,22]
CB is produced from petroleum feedstock, which has a negative impact on the environment [26]
Summary
Natural rubber (NR), mainly consisting of cis-1,4polyisoprene (cis-PI) with high elasticity, is acknowledged to be virtually irreplaceable in applications such as tires and seals. The CB concentration has a significant influence on the rubber composite properties; e.g., increasing the amount of CB has been shown to lead to enhanced tear strength, tensile strength, and elastic modulus [21,22]. Fullerene(C60) has been extensively used as a filler in polymer composites, especially for poly(3-hexylthiophene) in polymer-based solar cells for low-cost power production [30,31,32], and, in combination with epoxy, it has been shown to result in enhancements in the mechanical properties, electrical conductivity, flame resistance, and anti-corrosion [33]. Atomistic MD has been widely used in investigations of reinforced polymer nanocomposites, such simulations are computationally expensive To overcome this limitation, coarse-grained (CG) models have been developed to produce simplified representations of polymer molecules to access much larger time and length scales. Molecular visualizations were done using the Visual Molecular Dynamics (VMD) software (University of Illinois Urbana-Champaign, Urbana and Champaign, IL, USA) [74]
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