聚乙烯/银纳米颗粒复合物的分子动力学模拟研究

Molecular dynamics simulation of polyethylene/silver-nanoparticle composites

通过分子动力学模拟对聚乙烯/银纳米颗粒复合物的结构、极化率和红外光谱、热力学性质、力学特性进行计算,分析其随模拟温度和银颗粒尺寸的变化规律.模拟结果表明:聚乙烯/银纳米颗粒复合物为各向同性的无定形结构,温度升高可提高银纳米颗粒的分散均匀性;银纳米颗粒表面多个原子层呈现无定形状态,并在银颗粒和聚乙烯基体的界面形成电极化层,界面区域随颗粒尺寸和温度的增加分别减小和增加;与聚乙烯体系相比,聚乙烯/银纳米颗粒复合物的极化率高很多,且随温度的升高和银颗粒尺寸的减小而增大;银颗粒尺寸直接影响界面电偶极矩的强度和振动频率,红外光谱峰强度和峰位随颗粒尺寸发生变化;聚乙烯/银纳米颗粒复合物具有比聚乙烯体系更高的等容热容和与聚乙烯体系相反的负值热压力系数,热容随颗粒尺寸的变化较小,但随温度的升高而明显减小,具有显著的温度效应;热压力系数随温度的变化较小,但随颗粒尺寸的增加而减小,具有明显的尺度效应,温度稳定性更好;聚乙烯/银纳米颗粒复合物的力学特性表现出各向同性材料的弹性常数张量,具有比聚乙烯体系更高的杨氏模量和泊松比,并且都随温度的升高和银颗粒尺寸的增大而减小,加入银纳米颗粒可有效改善聚乙烯的力学性质.

Molecular dynamics simulations of polyethylene/silver-nanoparticle composites are implemented to calculate the structures,electrical,thermal and mechanical properties,thereby investigating their relationships with the nanoparticle dimension and simulation temperature.The results show that polyethylene/silver-nanoparticle composites are of isotropic amorphous structure,and the dispersion of nanoparticles in composite can be enhanced at a relatively higher temperature.Multi-layers of atoms on nanoparticle surface change into amorphous configurations,and electrical polarization interface layers are formed between silver nanoparticles and polyethylene matrix.The interface region shrinks and expends respectively with nanoparticle dimension and temperature increasing.Compared with polyethylene system,the polyethylene/silver-nanoparticle composite presents explicitly high polarizability which increases with temperature and nanoparticle size rising simultaneously.The silver nanopaticle dimension directly influences the intensity and frequency of interfacial dipole moment,resulting in corresponding variations of peak position and intensity in infrared spectrum.The polyethylene/silver-nanoparticle composite also shows higher isometric heat capacity and negative thermal pressure coefficient with better temperature stability,which decreases explicitly with temperature and nanoparticle size increasing respectively,than polyethylene system.The mechanical property of polyethylene/silver-nanoparticle composite shows isotropic elastic constant tensor with considerably higher Young modulus and Poisson ratio than the polyethylene system,both of which decrease with temperature and nanoparticle dimension increasing,which indicates the improvement on mechanical property with Ag nanoparticle filler.