| Rubber materials possess the characteristics of high elasticity,large deformation,and rapid recovery after deformation due to entropy elasticity,playing a pivotal role in many fields.However,rubber materials usually need mechanical reinforcement before they have engineering application value,and filled reinforcement strategy is a commonly used means.The introduction of nanomaterials can significantly improve the comprehensive mechanical properties of rubber.However,the filled strategy significantly increases the complexity of internal interactions within the rubber,leading to the deterioration of its high elasticity,hysteresis loss,and dynamic performance.Therefore,it is essential to balance the contradictions between reinforcement,toughening,and dynamic performance in rubber composites.Based on the above scientific issues,this paper selects two flexible substances(liquid metal and polymer-based particles)as reinforcing fillers.Starting from regulating the particle size of the fillers,improving the dispersion of the fillers,and optimizing the interfacial adhesion between the fillers and the matrix,rubber composites with mechanical strength,toughness,and optimized dynamic performance were prepared.In addition,this paper also adopts molecular dynamics simulation methods to construct a universal coarse-grained model similar to the experimental system,exploring the structure-property relationship between microstructure and performance.The main research contents and results are as follows:(1)The study investigated the effects of different phase structures and physical properties of nano liquid metal(LM)droplets undergoing solid-liquid phase transitions with temperature on the comprehensive mechanical properties of natural rubber(NR).The results showed that based on the liquid nature of LM at room temperature,LM can be uniformly dispersed in the NR matrix.At room temperature,the composites maintain the tensile crystallization properties of NR,and the deformable nature of LM allows the composites to combine high mechanical strength,toughness,and tear resistance.Additionally,the composites exhibit very low hysteresis loss.When the ambient temperature drops below the melting point and undercooling temperature of LM,LM undergoes two liquid-to-solid phase transitions,accompanied by an increase in modulus and volume.These two physical property changes enhance the interfacial physical interaction between the filler and the matrix,making solid LM particles more effective in mechanical reinforcement.Meanwhile,the uniform dispersion of LM keeps the hysteresis loss of the composites lower than that of traditional silica systems.In summary,the phase transition process of LM gives the composites temperature-responsive mechanical properties.(2)Focusing on how the structural changes of phase change materials before and after characteristic temperatures affect the properties of composites,a coarse-grained molecular dynamics simulation method was employed to construct a model of flexible filler-based polymer composites.The study investigated the influence of the flexibility and filling fraction of filler on the mechanical properties of the composites under different simulated temperature conditions,and analyzed the structure-property relationship between microstructure changes and performance.During non-equilibrium stretching,the evolution of filler topology at different temperatures was qualitatively compared through visual images.Secondly,by quantitatively calculating the structural parameters of each component,including the asphericity,relative shape anisotropy,and radius of gyration of the fillers,as well as the bond orientation and partial stress of the matrix chains,the changes in component structures with strain were tracked and analyzed.Finally,through triaxial stretching and cyclic stretching,the effects of temperature-dependent filler structure on the toughness and hysteresis loss of the composites were quantified.(3)A series of polymer-based micro/nanoparticles with different moduli were prepared through mechanical crushing and ball milling methods,and were then compounded with a rubber matrix.Depending on the chemical structures of the fillers and the matrix,dynamically covalent crosslinked networks and permanently crosslinked networks were established in the composites,respectively.Initially,the dispersion of the fillers within the matrix and the interfacial bonding strength were analyzed.Based on these findings,the focus was on investigating the effects of structural differences in polymer nanoparticles(PNPs)on the reinforcement,toughening,hysteresis loss,and dynamic properties of the composites.The results showed that low-modulus PNPs enabled the composites to exhibit optimal mechanical strength,while the toughening effect of the composites was evident with higher-modulus PNPs.By constructing a coarse-grained model similar to the experimental system,the stress contributions of PNPs with different modulus properties under interfacial co-crosslinking were simulated and calculated.This revealed the molecular mechanism of mechanical reinforcement by PNPs,which corroborated with the experimental results and conclusions.Benefiting from the good dispersion and interfacial adhesion of PNPs,the composites exhibited significant advantages in terms of hysteresis loss,rolling resistance,and dynamic heat generation performance compared to silica-based systems.The simple preparation method of PNPs achieved a balance between reinforcement,toughening,and hysteresis loss in the composites.Additionally,in the dynamically crosslinked network system,the interfacial co-crosslinking reaction between PNPs and the matrix significantly enhanced the high-temperature thermoplasticity of the system,enabling good reprocessability.Furthermore,simulation calculations revealed that accelerated dynamic bond exchange reactions in the interfacial region were a significant factor contributing to faster stress relaxation in the system. |
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