Revealing the toughening mechanism of graphene-polymer nanocomposite through molecular dynamics simulation

Advancing elastomer performance with dynamic bond networks in polymer-grafted single-chain nanoparticles: a molecular dynamics exploration

This research introduces a method to enhance the mechanical properties of elastomers by grafting polymer chains onto single-chain flexible nanoparticles (SCNPs) and incorporating dynamic functional groups. Drawing on developments in grafting polymers onto hard nanoparticle fillers, this method employs the distinct flexibility of SCNPs to diminish heterogeneity and enhance core size control. We use molecular dynamics (MD) simulations for a mesoscale analysis of structural properties, particularly the effects of dynamic functional group quantities and their distribution. The findings demonstrate that increased quantities of functional groups are correlated with enhanced mechanical strength and toughness, showing improved stress-strain responses and energy dissipation capabilities. Moreover, the uniformity in the distribution of these functional groups is crucial, promoting a more cohesive and stable dynamic bonding network. The insights gained from MD simulations not only advance our understanding of the microstructural control necessary for optimizing macroscopic properties, but also provide valuable guidance for the design and engineering of advanced polymer nanocomposites, thereby enhancing the material performance through strategic molecular design.

Modified magnesium oxide/silver nanoparticles reinforced poly (butylene succinate-co-terephthalate) composite biofilms for food packaging application

MgO/Ag nanoparticles (NPs) were surface-modified with titanate coupling agent titaniumtriisostearoylisopropoxide (NDZ-130). A new antibacterial biofilm for food packaging was synthesized by combining the modified MgO/Ag NPs with poly (butylene succinate-co-terephthalate) (PBST). The modification improved the compatibility between the MgO/Ag NPs and the PBST matrix. The effects of the modified MgO/Ag NPs on biofilm mechanical, barrier, thermal, antibacterial and food preservation properties were evaluated. Compared with the PBST/MgO/Ag composite film, the modified PBST/MgO/Ag composite film showed an increase in tensile strength (TS) of 8.71% and elongation at break (EB) of 16.66%, additionally decreasing water vapor permeability (WVP) by 42.86%. The composite film also exhibited over 95% inhibition of Staphylococcus aureus and Escherichia coli. The modified PBST/MgO/Ag composite film avoided microbial contamination and preserved cherry tomatoes while maintaining moisture and firmness for six days. All results indicated that the prepared biofilms have a high potential for use as food packaging films.

In Situ Grafted Composite Nanoparticles-Reinforced Polyurethane Elastomer Composites with Excellent Continuous Anti-Impact Performance

Polyurethane elastomer (PUE) has attracted much attention in impact energy absorption due to its impressive toughness and easy processability. However, the lack of continuous impact resistance limits its wider application. Here, an amino-siloxane (APTES) grafted WS₂-coated MWCNTs (A-WS₂@MWCNTs) filler was synthesized, and A-WS₂@MWCNTs/PUE was prepared by using the filler. Mechanical tests and impact damage characterization of pure PUE and composite PUE were carried out systematically. Compared with pure PUE, the static compressive strength and dynamic yield stress of A-WS₂@MWCNTs/PUE are increased by 144.2% and 331.7%, respectively. A-WS₂@MWCNTs/PUE remains intact after 10 consecutive impacts, while the pure PUE appears serious damage after only a one-time impact. The improvement of mechanical properties of A-WS₂@MWCNTs/PUE lies in the interfacial interaction and synergy of composite fillers. Microscopic morphology observation and damage analysis show that the composite nanofiller has suitable interfacial compatibility with the PUE matrix and can inhibit crack growth and expansion. Therefore, this experiment provides an experimental and theoretical basis for the preparation of PUE with excellent impact resistance, which will help PUE to be more widely used in the protection field.

Role of a nanoparticle network in polymer mechanical reinforcement: insights from molecular dynamics simulations

Fully understanding the mechanism by which nanoparticles (NPs) strengthen polymer matrices is crucial for fabricating high-performance polymer nanocomposites (PNCs). Herein, coarse-grained molecular dynamics simulations were adopted to explicitly investigate the reinforcing effect of a NP network. Our results revealed that increasing the NP-NP interactions induced the self-assembly of NPs into a three-dimensional (3D) network that reinforced the polymer matrix. The reinforcing mechanism of NP-NP interactions was quite different from that of NP-polymer interactions. The latter promoted the orientation of polymer chains to transfer the external stress, while the former distributed the stress throughout the NP network. This work revealed the mechanism by which the NP network reinforced the polymer matrix at the molecular level and also provided guidelines for developing high performance PNCs via interfacial modification.

Mechanical properties of graphene-reinforced aluminium composite with modified substrate surface: a molecular dynamics study

Due to its extraordinary properties, graphene has been widely used as reinforcing nanofillers to enhance the mechanical properties of polymer- or metal-based composites. However, the weak interfacial interaction between the matrix and graphene is still a major bottleneck that considerably hinders its reinforcing effectiveness and efficiency. This study presents an atomistic study via molecular dynamics simulation on a chemical modification strategy where the aluminium (Al) substrate is modified with Al₂O₃ (with or without covalent bonds formed between Al₂O₃ and graphene) or Al₄C₃ to achieve significantly improved interfacial shear strength and overall mechanical properties of graphene-reinforced aluminium (Al/Gr) composites. Numerical results show that this strategy works very well and among the three cases considered, modifying Al substrate by Al₂O₃ without covalent bonds formed at the interface between Al₂O₃ and graphene produces the strongest interfacial interaction and the best mechanical properties. In the presence of covalent bonds, however, the reinforcing effect is adversely affected due to the sp²-sp³ bond transformation which partially degrades graphene. The present work provides, for the first time, valuable insight into the role of substrate surface modification on the mechanical performance of Al/Gr nanocomposites.

Atomistic Insights into the Tunable Transition from Cavitation to Crazing in Diamond Nanothread-Reinforced Polymer Composites

Cavitation and crazing in thermosetting polymers can be sophisticatedly designed for valuable applications in optics, electronics, and biotechnology. It is a great challenge for numerical study to describe the formations of cavity and fibrils in polymer composite due to the complicated interfacial interaction. To explore this challenging task, we exploit a two-phase coarse-grained framework which serves as an efficient atomistic level-consistent approach to expose and predict the transition between cavitation and crazing in a polymeric system. The coarse-grained framework is utilized to transmit the information between single phase and interface in polymer composite, and the learning tasks of force field are fulfilled through parameterization of mechanical performances and structural characterizations. We elaborate on the intrinsic characteristics of the cavitation-crazing transition in diamond nanothread- (DNT-) reinforced polymethyl methacrylate composites, in which DNT plays a specific role of nanomodulator to tune the cavity volume ratio. The transition from cavitation to crazing can be induced through a novel dissipative mechanism of opening an interlocked network, in which case the DNT is stretched to the aligned fibrils and links crazing tightly by interfacial adhesion. The designed computational framework can broaden the scope of theoretical tools for providing better insights into the microstructure design of polymer composites.

Molecular dynamics simulation of thermo-mechanical behaviour of elastomer cross-linked via multifunctional zwitterions

Coarse-grained (CG) molecular dynamics simulations have been employed to study the thermo-mechanical response of a physically cross-linked network composed of zwitterionic moieties and fully flexible elastomeric polymer chains.

Simulational insights into the mechanical response of prestretched double network filled elastomers

This paper deals with molecular-dynamics simulations of the mechanical properties of prestretched double network filled elastomers. To this end, we firstly validated the accuracy of this method, and affirmed that the produced stress-strain characteristics were qualitatively consistent with Lesser's experimental results on the prestretched tri-block copolymers with a competitive double network. Secondly, we investigated the effect of the crosslinking network ratio on the mechanical properties of the prestretched double network homopolymers under uniaxial tension. We found that the prestretched double network contributes greatly to the enhanced tensile stress and ultimate strength at fracture, as well as to the lower permanent set (the residual strain) and dynamic hysteresis loss, both parallel and perpendicular to the prestretching direction. Notably, though, an anisotropic behavior was observed: in the parallel direction, both the first and the second crosslinked networks bore the external force; whereas in the perpendicular direction, only the second crosslinked network was relevantly effective. Finally, the polymer nanocomposites with a prestretched double network exhibited tensile mechanical properties similar to those of the studied homopolymers with prestretched double networks. Summing up the results, it can be concluded that the incorporation of prestretched double networks with a specified crosslinking network ratio seems to be a promising method for manipulating the mechanical properties of elastomers and their nanocomposites, as well as for introducing anisotropy in their mechanical response.

Self-Assembly of Block Copolymer Chains To Promote the Dispersion of Nanoparticles in Polymer Nanocomposites

In this paper we adopt molecular dynamics simulations to study the amphiphilic AB block copolymer (BCP) mediated nanoparticle (NP) dispersion in polymer nanocomposites (PNCs), with the A-block being compatible with the NPs and the B-block being miscible with the polymer matrix. The effects of the number and components of BCP, as well as the interaction strength between A-block and NPs on the spatial organization of NPs, are explored. We find that the increase of the fraction of the A-block brings different dispersion effect to NPs than that of B-block. We also find that the best dispersion state of the NPs occurs in the case of a moderate interaction strength between the A-block and the NPs. Meanwhile, the stress-strain behavior is probed. Our simulation results verify that adopting BCP is an effective way to adjust the dispersion of NPs in the polymer matrix, further to manipulate the mechanical properties.

Tuning the structure and mechanical property of polymer nanocomposites by employing anisotropic nanoparticles as netpoints

Introducing carbon nanotubes or graphene sheets into polymer matrices has received lots of scientific and technological attention. For the first time, we report a new kind of polymer nanocomposite (PNC) by means of employing anisotropic nanoparticles (NPs) as netpoints (referred to as an end-linked system), namely with NPs acting as netpoints to chemically connect the dual end-groups of each polymer chain to form a network. By taking advantage of this strategy, the anisotropic NPs can be uniformly distributed in the polymer matrix, with the NPs being separated via the connected polymer chains. And the separation distance between NPs, the stress-strain behavior and the dynamic hysteresis loss (HL) can be manipulated by varying the temperature and the polymer chain flexibility. Meanwhile, the physically mixed system is investigated by changing the interaction strength between polymer and NPs, and the temperature. It is emphasized that compared to the physically mixed system, the end-linked system which employs carbon nanotubes or graphene as netpoints possesses good thermal stability because of its thermodynamically stable morphology, exhibiting both excellent static and dynamic mechanical properties. These results help us to design and fabricate high performance and multi-functional PNCs filled with carbon nanotubes or graphene, facilitating the potentially large industrial application of these nanomaterials.