The mechanical properties of polymer nanocomposites (PNCs) depend sensitively on the structure (e.g., orientation, dispersion, and so on) of the incorporated nanofillers. Many studies have shown that the alignment of anisotropic nanofillers can improve the mechanical properties of PNCs. However, achieving this alignment typically requires complex preparation processes. To address this challenge, researchers have introduced dynamic covalent bonds to form reversible cross-linked polymer systems, which would lead to unique properties, such as self-healing, recyclability, and reprocessibility. In addition, inspired by the above ideas, we introduce nanorods as fillers into a linear vitrimer system to form nanorod vitrimer composites (NVCs). In NVCs, we can easily manipulate the alignment of the nanorods due to bond exchange reactions (BERs) in the vitrimer matrices. By using coarse-grained molecular dynamics (CGMD) simulations, we systematically investigate the factors affecting the nanorod orientation in NVCs. We find that the main factor affecting the nanorod orientation is the network rearrangement caused by BERs. Specifically, the BER potential barrier (ΔE sw) directly determines the probability of BERs’ occurrence. At the same time, the increase of the interfacial interaction between polymer chains and nanorods (εnp) confines the motion of the active beads, which slows down the rate of BERs. Additionally, the impact of temperature (T) and aspect ratio (ld) on the orientation of nanorods during uniaxial stretching or stress relaxation are also discussed. Finally, by combining uniaxial stretching and stress relaxation processes, we elucidate the orientation retention mechanism of NVCs and demonstrate the mechanical property enhancement phenomenon of the pre-oriented NVC systems. This work provides a simple strategy for manipulating the nanorod alignment in vitrimer matrices and uncovers guidelines for designing new functional polymer vitrimer nanocomposites at the molecular level.

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Densely grafted polymer chains onto spherical nanoparticles produce a diverse range of conformations. At high grafting densities, the corona region near the nanoparticle surface undergoes intense confinement due to a high concentration of chains in the concentrated polymer brush (CPB) region, which results in strong stretching for portions of the chains located within. In contrast, a semi-dilute polymer brush (SDPB) forms farther away from the core and offers reduced confinement for the polymer and more ideal conformations. However, conventional experimental methods are limited in their ability to provide detailed information on individual segments of grafted polymers in these regions; hence, molecular dynamics (MD) simulations are essential for gaining comprehensive insights into the behavior of the grafted chains. This study aims to explore the variations in polymer structure and dynamics that occur along the contour of the grafted chains as influenced by spatial confinement. We focus on the motions and relative positions of each bead along grafted polymers. Our results show that only the initial few grafted beads near the nanoparticle surface exhibit the strong stretching attributed segments in the CPB region of the brush. Increased grafting density or decreased chain flexibility leads to more stretched grafted chains and more aligned bond vectors. As a result, the relaxation dynamics of local regions of the polymer are also strongly influenced by these parameters. Although the grafted beads in the interior of the CPB region are highly sensitive to these parameters, those farther from the nanoparticle core experience significantly diminished effects. In comparison to the Daoud–Cotton (DC) model’s predictions of CPB size, beads near the nanoparticle surface show slower dynamic decay, especially in high grafting densities, aligning with the DC model’s estimates. Finally, we compare our simulations to previous works for additional insight into polymer-grafted nanoparticles.

A coarse-grained molecular dynamics simulation was employed to examine the relationship between the morphology of carbon black particles and the mechanical properties of elastomer nanocomposites.

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This work investigates the compatibility of ten commercially available accelerators and ten antioxidants with three types of rubber by using molecular dynamics simulation. By constructing fully atomistic models of rubber and small molecules, firstly, the length and number of polymer chains, as well as the number of small molecules are optimized by calculating the solubility parameter. All simulated systems are guaranteed to reach equilibrium by checking the change of the density and energy. Then this work shows that the simulated results match well with each other, which are obtained from the value and the difference of the binding energy of the rubber systems, fractional free volume of the rubber systems, and self-diffusion coefficient of small molecules calculated from the mean square displacement-time curve. And some small molecules which are more compatible with rubbers are found. More importantly, this study can further determine their compatibility preference by calculating the partition coefficients of small molecules in the rubber blends. Meanwhile, the temperature effect on the change of the compatibility is as well examined. In general, this work provides some guidance for determining the compatibility between rubber and small-molecule additives, enabling the design of high-performance rubber materials.

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Background:Coloring is an important external quality of ‘Fuji’ apple (Malus domestica Borkh.) and there are two color patterns of apple peels, i.e., stripe and blush. The objectives of this study were to reveal the anthocyanin biosynthesis metabolic pathway in striped and blushed peels of Malus domestica using metabolomics and transcriptomics, to identify different anthocyanin metabolites, and to analyze the differentially expressed genes involved in anthocyanin biosynthesis.Result:The metabolite concentration and gene expression were profiled in the striped and blushed fruit peels of apple harvested at three ripening periods to elucidate the color formation mechanism. At the green fruit period, there were 83 DAMs,including 30 flavonoids, 674 DEGs (521 up-regulated and 153 down-regulated),including 3 MYB related genes (up-regulated, LOC103415449, LOC103421948, LOC103432338) and 2 bHLH genes(up-regulated, LOC103436250, LOC103437863) between striped and blushed apple.At the color turning period, there were 48 DAMs,including 20 flavonoids, 880 DEGs (274 up-regulated and 606 down-regulated), including 3 differentially expressed E2.3.1.133, HCT genes(down-regulated), 2 differentially expressed F3H genes (down-regulated), 1 differentially expressed BZ1 gene (down-regulated) and 2 differentially expressed ANS genes (up-regulated) and 2 up-regulated MYB related genes (LOC103411576, LOC103412495), 5 down-regulated MYB related genes(LOC103400953, LOC103408672, LOC103415404, LOC103420697, LOC103421948), 1 differentially expressed bHLH gene(down-regulated, LOC103400870). At the complete coloring period，there were 95 DAMs,including 34 flavonoids, 2258 DEGs (1159 up- and 1099 down-regulated), including 3 differentially expressed E2.3.1.133, HCT genes(down-regulated), 1 differentially expressed E2.3.1.133, HCT genes(up-regulated), 2 differentially expressed CYP98A genes (up-regulated), 4 differentially expressed CHS genes (up-regulated), 2 differentially expressed E5.5.1.6 genes(up-regulated), 2 differentially expressed CYP75B1 genes (up-regulated), 2 differentially expressed F3R genes (up-regulated), 2 differentially expressed ANS genes (up-regulated), 1 differentially expressed DFR genes (up-regulated), 2 differentially expressed BZ1 genes (up-regulated) and 1 differentially expressed MYB related gene (up-regulated, LOC103401575) .There were both 10 kinds of cyanidin in apple peel at color turning period and complete coloring period, Keracyanin and Cyanin were up-regulated at color turning period and Cyanidin-3-O-(6''-O-malonyl)glucoside was up-regulated at complete coloring period.Conclusions: Our researches provide important information on the anthocyanin metabolites and the candidate genes involved in the anthocyanin biosynthesis pathways of Fuji apple in M.domestcia.