Biological staggered composites, like bone, nacre, and dentin, possess the superior capacity of energy dissipation than that of conventional materials. In these nanocomposites, different staggered microstructures are widely observed, for example, symmetric staggered structures with regular platelet layouts and asymmetric staggered structures with offset and stairwise platelet layouts. In addition, the thickness of platelets in these biological materials is at the nanoscale, and the distance between the adjacent ends of platelets is large enough in staggered structures, which indicates the interface effect and tension region cannot be ignored in staggered nanocomposites. In order to investigate the possible synergistic effect of the platelet layouts, interface effects, and tension region on the dynamic properties of the nanocomposites, a generalized tension-shear chain model (TSCM) with tension region (TR) is proposed. According to the analytical solutions derived, the staggered nanocomposites with optimal structures can be designed to obtain superior energy dissipation capacity. Considering different loading frequencies in natural environment, the optimal dynamic properties of nacre can be achieved with a regular staggering platelet distribution, while the optimal dynamic properties of bone can be achieved when the number of periodic stairwise staggering platelets is appropriately smaller. These optimal platelet layouts in nacre and bone are consistent with the experimental results reported in many literatures. Therefore, the energy dissipation capacity of staggered nanocomposites can be highly improved, based on the profound understanding of the damping mechanism in biological nanocomposites.
Polydimethylsiloxane/silica (PDMS/SiO2) particle-reinforced nanocomposites prepared at the present study are typical viscoelastic materials. Due to the high surface-to-volume ratio of the SiO2 nanoparticles, the interface effects on the overall properties of the nanocomposites cannot be ignored. In order to investigate the interface effects on the viscoelastic properties of the nanocomposites, a multiscale model is established at the present study, combining the molecular dynamics (MD) model of the interface at the nanoscale and the unit cell model of the nanocomposites at the mesoscale. In the MD model of the interface, the viscoelastic properties of the interphase region influenced by the interface are found to be different from that of the pure PDMS matrix and the bulk SiO2. Because of the polymer chains subject to different restrictions existing in the interphase region, this region can possess high stiffness and damping properties simultaneously. The interphase parameters can be determined by the inverse multiscale simulation method, taking advantage of both the numerical model and the experimental results. Due to the interface effects, as demonstrated by the unit-cell model, the dynamic shear dynamic moduli of the nanocomposites can be simultaneously improved by several times to an order of magnitude higher than that of the matrix, in consistent with experimental results. Thus, the mechanism of the interface effects enhancing the viscoelastic properties of the PDMS/SiO2 nanocomposites can be revealed at the present study, which can be useful for the design of viscoelastic nanocomposites with high stiffness and damping properties.
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