Atomic scale characterization of interfacial properties of polymer/metal composites
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摘要: 聚合物/金属界面性能显著影响由金属和聚合物形成的复合材料的力学性能。结合热力学理论分析和分子动力学模拟,系统计算了几种典型聚合物(PS、PE、PP)和金属(Al、Ni、Cu、Fe)形成界面的断裂能及界面强度。聚合物/金属界面的界面应力随着界面位移的增加先增加,达到强度后进入界面损伤阶段,界面应力减小,直到界面完全断裂,应力降低为零。不同聚合物/金属界面的强度大小变化趋势与界面断裂能一致,界面断裂能模拟与理论计算结果基本一致。聚合物/金属界面断裂能与金属表面能强弱有关,由于金属的表面能随着Ni、Fe、Cu、Al的顺序逐渐减小,相应形成的聚合物/金属界面的断裂能也按照聚合物/Ni、聚合物/Fe、聚合物/Cu、聚合物/Al的顺序逐渐减小;同种金属情况下,PE/金属和PP/金属的界面强度相近,且均小于PS/金属的界面强度。进一步,界面的损伤通过聚合物的自由体积演化进行了表征。研究结果为聚合物/金属复合材料的选材、设计以及应用提供了依据。Abstract: The interfacial properties of polymer/metal significantly affect the mechanical properties of composites formed by metal and polymer. Combined with thermodynamic theoretical analysis and molecular dynamics simulation, the interface fracture energy and interface strength of the interface formed by several typical polymers (PS, PE, PP) and metals (Al, Ni, Cu, Fe) were systematically calculated. With the increase of interface displacement, the interface stress of polymer/metal interface first increases, then reaches the strength and enters the interface damage stage, and the interface stress decreases until the interface is completely broken, and the stress decreases to zero. The strength change trend of different polymer/metal interfaces is consistent with the interface fracture energy, and the simulation results of interface fracture energy are basically consistent with the theoretical calculation results. The interface fracture energy of polymer/metal interface is related to the surface energy of metal. As the surface energy of metal decreases with the order of Ni, Fe, Cu and Al, the interface fracture energy of polymer/metal interface also decreases with the order of polymer /Ni, polymer /Fe, polymer /Cu and polymer /Al. Under the same metal condition, the interface strength of PE/ metal and PP/ metal is similar, and both are smaller than that of PS/ metal. Furthermore, the interface damage was characterized by the free volume evolution of the polymer. The research results provide a basis for material selection, design and application of polymer/metal composites.
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图 2 界面应力-位移曲线:(a)PE/Al、PE/Cu、PE/Fe和PE/Ni;(b)PP/Al、PP/Cu、PP/Fe和PP/Ni;(c)PS/Al、PS/Cu、PS/Fe和PS/Ni;(d)聚合物/金属界面强度比较
Figure 2. Interfacial stress-interfacial displacement curves: (a) PE/Al, PE/Cu, PE/Fe and PE/Ni; (b) PP/Al, PP/Cu, PP/Fe and PP/Ni; (c) PS/Al, PS/Cu, PS/Fe and PS/Ni; (d) Interface strength of polymer/metal interface models
表 1 聚合物和金属的热力学参数
Table 1. Thermodynamic parameters of polymers and metals
Material h/nm SV/(J·mol−1·K−1) H/(kJ·mol−1) V/(cm3·mol−1) γ/(J·m−2) Ni 0.27 10.12 17.47 6.59 1.19 Cu 0.27 9.58 13.00 7.10 0.76 Fe 0.28 8.23 14.90 7.10 0.78 Al 0.25 11.43 10.67 10.00 0.49 PP 1.16 19.86 8.70 2150 0.15 PE 0.81 11.26 4.11 94.70 0.06 PS 1.53 19.49 10.00 594.00 0.08 Notes:PP—Polypropylene; PE—Polyethylene; PS—Polystyrene; h is the equilibrium distance between atoms, Sv is the vibrational part of melting entropy, H is the melting enthalpy, V is the molar volume, and γ is the free energy of metal and polymer. 表 2 聚合物和金属间的界面自由能
$ {\gamma _{P - M}} $ Table 2. Interface energy of polymer/metal
$ {\gamma _{P - M}} $ J·m−2 PP PE PS Ni 0.670 0.627 0.636 Cu 0.455 0.412 0.421 Fe 0.465 0.422 0.431 Al 0.320 0.277 0.286 表 3 聚合物和金属的表面能
Table 3. Surface energy of polymers and metals
Metal γm/(J·m−2) Polymer γp/(J·m−2) Ni 2.426 PP 0.027 Cu 2.166 PE 0.030 Fe 2.222 PS 0.030 Al 1.347 Notes:γp is the surface energy of polymer and γm is the surface energy of metal. 表 4 聚合物/金属的界面断裂能
$ \Gamma $ Table 4. Interface fracture energy of polymer/metal
$ \Gamma $ J·m−2 PP PE PS Ni 1.783 1.830 1.820 Cu 1.738 1.785 1.775 Fe 1.784 1.831 1.821 Al 1.054 1.101 1.091 表 5 聚合物/金属界面模型的尺寸
Table 5. Size of polymer/metal interface models
Model PE/Al PE/Ni PE/Fe PE/Cu PP/Al PP/Ni Size/nm 3.65×3.65×5.92 3.52×3.52×5.16 3.58×3.58×5.15 3.62×3.61×5.24 4.05×4.05×5.87 4.23×4.23×4.78 Model PP/Fe PP/Cu PS/Al PS/Ni PS/Fe PS/Cu Size/nm 3.94×3.94×5.33 3.98×3.98×5.46 4.45×4.45×5.77 4.23×4.23×5.41 4.30×4.30×6.82 4.33×4.33×6.71 -
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