Structure–Mechanics Relation of Natural Rubber: Insights from Molecular Dynamics Simulations

Abstract

Attributed to its strain-induced crystallization (SIC), natural rubber (NR) exhibits more excellent mechanical properties compared to other elastomeric materials and has been attracting numerous scientific and technological attention. However, a systematical understanding of the structure–mechanics relation of NR is still lacking. Herein, for the first time, we employ molecular dynamics simulation to examine the effects of the key structural factors on the SIC and mechanical properties at the molecular level. We examine the effects of phospholipid and protein mass fraction (ω), the strength of hydrogen-bond interaction (εH), and the strength of non-hydrogen-bond interaction (εNH) on structural morphology, dynamic behavior, and mechanical properties. NR tends to form local clusters due to the hydrogen-bond interaction formed between phospholipids or proteins and chain ends, which is absent in the case of cis-1,4-polyisoprene (PIP). The polymer chain mobility of NR is retarded due to the formed clusters or even physical network at great εH and high ω. Interestingly, we find that the stress–strain behavior of NR is greatly manipulated by εH and ω, as evidenced by the increase of the chain orientation and the SIC, compared with the cases of PIP. This underlying mechanism results from the alignment of the molecular chains induced by the formed clusters along the deformed direction, and the clusters during the deformation become more stable, particularly at great εH. Lastly, we adopt a machine learning algorithm named extreme gradient boosting via data augmentation, finding that εH has the most significant influencing weight factor on the stress–strain behavior of NR. In general, this work demonstrates a detailed molecular-level structure–mechanics relation of NR and provides some rational guidelines for experimentally designing and synthesizing biomimetic NR.

Dispersion and Diffusion Mechanism of Nanofillers with Different Geometries in Bottlebrush Polymers: Insights from Molecular Dynamics Simulation

“…For the NRs, K θ = 20­(ε·rad –2 ) and the bond angle θ 0 = 180°. These potentials have been validated to be efficient in previous research studies. − The periodic boundary conditions are utilized in all three directions to eliminate the edge effects during the simulation.…”

Substantial Effect of Terminal Groups in cis-Polyisoprene: A Multiscale Molecular Dynamics Simulation Study

“…The natural rubber from Hevea brasiliensis consists of rubber particles, protein, lipid, carbohydrates, metal ions, and others. − Hevea natural rubber is mainly composed of cis -1,4-polyisoprene and two kinds of functional terminal groups. , The basic structure of natural rubber consists of cis -1,4-polyisoprene, ω-terminal and α-terminal. ω-Terminal contains a dimethylallyl group and two to three trans -isoprenes. ,, α-Terminal consists of hydroxy, ester, and phosphate groups. ,,− The resistance of rubber to the deformation and fracture before vulcanization is called the green strength .…”

“…The natural rubber from Hevea brasiliensis consists of rubber particles, protein, lipid, carbohydrates, metal ions, and others. − Hevea natural rubber is mainly composed of cis -1,4-polyisoprene and two kinds of functional terminal groups. , The basic structure of natural rubber consists of cis -1,4-polyisoprene, ω-terminal and α-terminal. ω-Terminal contains a dimethylallyl group and two to three trans -isoprenes. ,, α-Terminal consists of hydroxy, ester, and phosphate groups. ,,− The resistance of rubber to the deformation and fracture before vulcanization is called the green strength . The high green strength of Hevea natural rubber, i.e ., the increase in the sigmoidal stress of NR with increasing strain, is ascribed to these functional groups. − It is speculated that protein is bonded with ω-terminal and lipid is bonded with α-terminal and that both of these terminals can form branch points in the polymer chains with them .…”

Mechanically Robust and Self-Healing Elastomers Based on Dynamic Oxime–Carbamate Bonds: A Combined Experiment and All-Atom Simulation Study

“…When heated to a certain temperature, it can easily dissociate into isocyanate groups and oxime groups, and simultaneously also reform the oxime–carbamate bond. − Therefore, dynamic oxime–carbamate bonds are introduced into the polymer network to prepare elastomers with excellent self-healing properties. , However, the self-healing behavior and mechanisms of polyurethane based on dynamic oxime–carbamate bonds at the molecular level are not well understood. Our previous works have demonstrated the applicability of molecular dynamics (MD) simulations to study the dynamic and static mechanical properties of elastomers and to reveal their intrinsic mechanisms. − To date, although a large number of experimental studies have successfully designed and prepared elastomers with excellent self-healing ability, there are very few self-healing elastomers based on dynamic covalent bonds analyzed by a combination of experiments and MD simulations . In contrast to experiments, MD simulations have been used extensively to study the self-healing behavior and mechanisms of polymer networks at the molecular level. − To further improve the design and optimization of self-healing polymer networks, it is important to clarify the self-healing behavior and mechanisms at the molecular level. , …”