The transport of nanoparticles in semiflexible networks, which form diverse principal structural components throughout living systems, is important in biology and biomedical applications. By combining large-scale molecular simulations as well as theoretical analysis, we demonstrate here that nanoparticles in polymer networks with semiflexible strands possess enhanced heterogeneous diffusion characterized by more evident hopping dynamics. Particularly, the hopping energy barrier approximates to linear dependence on confinement parameters in the regime of moderate rigidity, in contrast to the quadratic dependence of both its soft and hard counterparts. This nonmonotonic feature can be attributed to the competition between the conformation entropy and the bending energy regulated by the chain rigidity, captured by developing an analytical model of a hopping energy barrier. Moreover, these theoretical results agree reasonably well with previous experiments. The findings bear significance in unraveling the fundamental physics of substance transport confined in network-topological environments and would provide an explanation for the dynamics diversity of nanoparticles within various networks, biological or synthetic.
Ligaments are flexible and stiff tissues around joints to support body movements, showing superior toughness and fatigue-resistance. Such a combination of mechanical properties is rarely seen in synthetic elastomers because stretchability, stiffness, toughness, and fatigue resistance are seemingly incompatible in materials design. Here we resolve this long-standing mismatch through a hierarchical crosslinking design. The obtained elastomer can endure 30,000% stretch and exhibit a Young’s modulus of 18 MPa and toughness of 228 MJ m−3, outperforming all the reported synthetic elastomers. Furthermore, the fatigue threshold is as high as 2,682 J m−2, the same order of magnitude as the ligaments (~1,000 J m−2). We reveal that the dynamic double-crosslinking network composed of Li+-O interactions and PMMA nanoaggregates allows for a hierarchical energy dissipation, enabling the elastomers as artificial ligaments in soft robotics.
Harnessing anisotropic interactions in a DNA-mediated nanoparticle assembly holds great promise as a rational strategy to advance this important area. Here, using molecular dynamics simulations, we report the formation of novel hierarchical crystalline assemblies of Janus nanoparticles functionalized with two types of DNA chains (DNA-JNPs). We find that in addition to the primary nanoparticle crystallization into face-centered cubic (FCC) structure, sequence-specific DNA hybridization events further direct the rotational orientation of the DNA-JNPs to diverse secondary crystalline phases including simple cubic (SC), tetragonally ordered cylinder (P4), and lamella (L) structures, which are mapped in the phase diagrams relating to various asymmetric parameters. The crystallization dynamics of such hierarchical crystals is featured by two consequent processes: entropy-dominated translational order for the primary crystalline structure and enthalpy-dominated rotational order for the secondary crystalline structure. For DNA-JNPs with high asymmetry in DNA sequence length, tetrahedral nanoclusters tend to be favored, which is revealed to be governed by the conformational entropy penalty caused by bounded DNA chains. This work might bear important consequences for constructing new classes of nanoparticle crystals with designed structures and properties at multiple levels and in a predictable manner.
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