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As a typical viscoelastic material, solid propellants have a large difference in mechanical properties under static and dynamic loading. This variability is manifested in the difference in values of the relaxation modulus and dynamic modulus, which serve as the entry point for studying the dynamic and static mechanical properties of propellants. The relaxation modulus and dynamic modulus have a clear integral relationship in theory, but their consistency in engineering practice has never been verified. In this paper, by introducing the “catch-up factor λ” and “waiting factor γ”, a method for the inter-conversion of the dynamic storage modulus and relaxation modulus of HTPB propellant is established, and the consistency between them is verified. The results show that the time region of the calculated conversion values of the relaxation modulus obtained by this method covers 10−8–104 s, spanning twelve orders of magnitude. Compared to that of the relaxation modulus (10−4–104 s, spanning eight orders of magnitude), an expansion of four orders of magnitude is achieved. This enhances the expression ability of the relaxation modulus on the mechanical properties of the propellant. Furthermore, when the conversion method is applied to the dynamic–static modulus conversion of the other two HTPB propellants, the results show that the correlation coefficient between the calculated and measured conversion values is R2 > 0.933. This proves the applicability of this method to the dynamic–static modulus conversion of other types of HTPB propellants. It was also found that λ and γ have the same universal optimal value for different HTPB propellants. As a bridge for static and dynamic modulus conversion, this method greatly expands the expression ability of the relaxation modulus and dynamic storage modulus on the mechanical properties of the HTPB propellant, which is of great significance in the research into the mechanical properties of the propellant.

Articular cartilage has limited self-repair capacity due to the lack of vascularization, innervation and lymphatic networks. Biomimetic scaffolds with features of the extracellular matrix (ECM) of cartilage are advantageous to repair the injured cartilage tissue, but it remains a challenge to regulate its shear viscoelasticity to meet the needs of applications as articular cartilages. Fiber reinforced hydrogel is of great significance for their clinical application as cartilage tissue engineering scaffolds, especially for repairing the fibrocartilage tissue like meniscus or temporomandibular joint disc. In order to promote the shear viscoelasticity of alginate hydrogels, which was seldom studied, electrospinning PCL nanofiber layers were added into the alginate hydrogels to prepare PCL nanofibers reinforced alginate hydrogel composites (PNRAHCs). Compared with neat alginate hydrogel scaffolds, the PNRAHCs presented coral-like structure and spider web-like structure, and some PCL nanofibers form reinforced fiber bundles. Those special structures make the PNRAHCs have higher porosity, higher shear storage modulus and higher shear loss modulus than the neat alginate hydrogels, indicating better shear mechanical properties. They have the potential to be applied as the scaffolds to repair fibrocartilage tissues.

Ecological impact of improper disposal of growing agricultural waste is huge. These low cost, renewable, and biodegradable materials can be utilized in production of eco-friendly polymer composite. However, further property enhancement can be achieved by hybridization. This work evaluated the feasibility of enhancing the properties of Bambara nut shell particulate (BNSp) reinforced polyester composite by incorporation of clay. Ultimate tensile strength (UTS) of 23.98 MPa was recorded for the hybrid composite of 3 wt% clay + 12 wt% BNSp compared to 19.86 MPa for 12wt% BNSp polymer composite. DMA analysis showed a damping factor of 0.586 at 89.51 °C for 3 wt% clay + 12 wt% BNSp composite. Clay addition modifies and improves the properties of agro-waste reinforced polymer composites with clay/BNSp/polyester composite exhibiting higher mechanical properties compared to the BNSp reinforced polyester composite due to the ability of the clay to insert themselves between the layers of the polyester matrix. This work also showed that Bambara nut is a potential low-cost filler material for polymer composites and can be used in areas requiring medium strength but lightweight materials.

Epoxy with low viscosity and good fluidity before curing has been widely applied in the packaging of electronic and electrical devices. Nevertheless, its low flexibility and toughness renders the requirement of property improvement before it can be widely acceptable in dynamic loading applications. This study investigates the possible use of 2-hydroxyethyl methacrylate (HEMA) toughening agent and nano-powders, such as alumina, silicon dioxide, and carbon black, to form epoxy composites for dynamic property improvement. Considering the different combinations of the nano-powders and HEMA toughener, the Taguchi method with an L9 orthogonal array was adopted for composition optimization. The dynamic storage modulus and loss tangent of the prepared specimen were measured by employing a dynamic mechanical analyzer. With polynomial regression, the curve-fitted relationships of the glass transition temperature and storage modulus with respect to the design factors were obtained. It was found that although the raise in the weight fraction of nano-powders was beneficial in increasing the rigidity of the epoxy composite, an optimal amount of HEMA toughener existed for its best damping improvement.

The decellularization of organs has attracted attention as a new functional methodology for regenerative medicine based on tissue engineering. In previous work we developed an L-ECM (Extracellular Matrix) as a substrate-solubilized decellularized liver and demonstrated its effectiveness as a substrate for culturing and transplantation. Importantly, the physical properties of the substrate constitute important factors that control cell behavior. In this study, we aimed to quantify the physical properties of L-ECM and L-ECM gels. L-ECM was prepared as a liver-specific matrix substrate from solubilized decellularized porcine liver. In comparison to type I collagen, L-ECM yielded a lower elasticity and exhibited an abrupt decrease in its elastic modulus at 37 °C. Its elastic modulus increased at increased temperatures, and the storage elastic modulus value never fell below the loss modulus value. An increase in the gel concentration of L-ECM resulted in a decrease in the biodegradation rate and in an increase in mechanical strength. The reported properties of L-ECM gel (10 mg/mL) were equivalent to those of collagen gel (3 mg/mL), which is commonly used in regenerative medicine and gel cultures. Based on reported findings, the physical properties of the novel functional substrate for culturing and regenerative medicine L-ECM were quantified.

The structural breakup and recovery of coastal mud are closely related to wave propagation, mud transportation, and coastal morphology evolution. Due to the influence of climate, topography, and other factors, the wave frequency in marine environments is more variable than fixed. To investigate the mud structural breakup and recovery process under oscillatory shear loads with different frequencies, a series of oscillatory rheological experiments of the coastal mud collected from the tidal flats of Zhairuoshan Island, Zhejiang province, China, were carried out. The results revealed that the structural breakup of coastal mud had a two-step transition process. The fluidization occurs more rapidly at higher frequencies, but the influence of frequency on the two yield stresses is limited. In addition, frequency has a complex effect on the structural recovery of coastal mud. The normalized equilibrium storage modulus (G∞′/G0′) does not change monotonically with frequency. Moreover, the viscosity quickly approaches equilibrium when a shear load is applied. After that, when a low-frequency load is applied, G∞′/G0′ is no longer related to the pre-shear duration. However, when a high-frequency load is applied, G∞′/G0′ of the mud sample pre-sheared for 500 s is significantly larger than that of the sample pre-sheared to the minimum viscosity. This study is anticipated to provide reference and supplementary test data for understanding the interaction between waves of different frequencies and muddy seabed.

Thermal and rheological properties of plant-based natural filler-reinforced polyethylene bio-composites applying various filler loadings as well as the impacts of the different compatibilizers were investigated by means of differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA). As lignocellulosic materials, such as rice-husk flour and wood flour, are eco-friendly biomaterials and a thermoplastic polymer, for example, high-density polyethylene, has good physico-mechanical and thermal properties, therefore their bio-composites can combine and utilize these two advantages at the same time. The temperature of the α-relaxation (Tα) slightly increased and melting temperatures (Tm) of the matrix polymer in the case of the studied bio-composites did not shift significantly as the filler loading changed, because the rigid interphase hinders the motion of polymer segments resulting in the increase in Tα and only weak interactions developed at the interface between the matrix polymer and the reinforcement in the case of non-compatibilized composites. However, compatibility between the reinforcement and the matrix polymer was enhanced by incorporating compatibilizers, which further improved stiffness. From the DMTA experiment, the reinforcements result in composite samples having higher storage modulus (E′) than the neat polymer sample, indicating that incorporating lignocellulosic filler increased their stiffness.

Dynamic Mechanical Analysis (DMA) allows for the measurement of the complex shear modulus of an elastomer. Measurements at frequencies above the frequency range of the device can be reached thanks to the Time–Temperature Equivalence principle. Yet, frequencies higher than a few kHz are not attainable. Here, we propose a method exploiting the physics of bubble phononic crystals to measure the complex shear modulus at frequencies of a few tens of kHz. The idea is to fabricate a phononic crystal by creating a period arrangement of bubbles in the elastomer of interest, here PolyDiMethylSiloxane (PDMS), and to measure its transmission against frequency. Fitting the results with an analytic model provides both the loss and storage moduli. Physically, the shear storage modulus drives the position of the dip observed in transmission while the loss modulus controls the damping, and thus the level of transmission. Using this method, we are able to compare the high-frequency rheological properties of two commercial PDMS and to monitor the ageing process.

Rechargeable batteries paired with sodium metal anodes are considered to be one of the most promising high-energy and low-cost energy-storage systems. However, the use of highly reactive sodium metal and the formation of sodium dendrites during battery operation have caused safety concerns, especially when highly flammable liquid electrolytes are used. Here we design and develop solvent-free solid polymer electrolytes (SPEs) based on a perfluoropolyether-terminated polyethylene oxide (PEO)-based block copolymer for safe and stable all-solid-state sodium metal batteries. Compared with traditional PEO SPEs, our results suggest that block copolymer design allows for the formation of self-assembled nanostructures leading to high storage modulus at elevated temperatures with the PEO domains providing transport channels even at high salt concentration (ethylene oxide/sodium = 8/2). Moreover, it is demonstrated that the incorporation of perfluoropolyether segments enhances the Na + transference number of the electrolyte to 0.46 at 80 °C and enables a stable solid electrolyte interface. The new SPE exhibits highly stable symmetric cell-cycling performance at high current density (0.5 mA cm −2 and 1.0 mAh cm −2 , up to 1,000 h). Finally, the assembled all-solid-state sodium metal batteries demonstrate outstanding capacity retention, long-term charge/discharge stability (Coulombic efficiency, 99.91%; >900 cycles with Na 3 V 2 (PO 4 ) 3 cathode) and good capability with high loading NaFePO 4 cathode (>1 mAh cm −2 ). Rechargeable batteries with sodium metal anodes are promising as energy-storage systems despite safety concerns related to reactivity and dendrite formation. Solvent-free perfluoropolyether-based electrolytes are now reported for safe and stable all-solid-state sodium metal batteries.

Background: Inspired by structural hierarchies and the related excellent mechanical properties of biological materials, we created a smoothly graded micro- to nanoporous structure from a thermoplastic polymer. Results: The viscoelastic properties for the different pore sizes were investigated in the glassy regime by dynamic flat-punch indentation. Interestingly, the storage modulus was observed to increase with increasing pore-area fraction. Conclusion: This outcome appears counterintuitive at first sight, but can be rationalized by an increase of the pore wall thickness as determined by our quantitative analysis of the pore structure. Therefore, our approach represents a non-chemical way to tune the elastic properties and their local variation for a broad range of polymers by adjusting the pore size gradient.