Weng Can, Yang Dongjiao, Zhou Mingyong
College of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China.
Micromachines (Basel). 2019 Sep 23;10(10):636. doi: 10.3390/mi10100636.
Injection molding is one of the most potential techniques for fabricating polymeric products in large numbers. The filling process, but also the demolding process, influence the quality of injection-molded nanostructures. In this study, nano-cavities with different depth-to-width ratios (D/W) were built and molecular dynamics simulations on the demolding process were conducted. Conformation change and density distribution were analyzed. Interfacial adhesion was utilized to investigate the interaction mechanism between polypropylene (PP) and nickel mold insert. The results show that the separation would first happen at the shoulder of the nanostructures. Nanostructures and the whole PP layer are both stretched, resulting in a sharp decrease in average density after demolding. The largest increase in the radius of gyration and lowest velocity can be observed in 3:1 nanostructure during the separation. Deformation on nanostructure occurs, but nevertheless the whole structure is still in good shape. The adhesion energy gets higher with the increase of D/W. The demolding force increases quickly to the peak point and then gradually decreases to zero. The majority of the force comes from the adhesion and friction on the nanostructure due to the interfacial interaction.
注塑成型是大规模制造聚合物产品最具潜力的技术之一。填充过程以及脱模过程都会影响注塑纳米结构的质量。在本研究中，构建了具有不同深宽比（D/W）的纳米腔，并对脱模过程进行了分子动力学模拟。分析了构象变化和密度分布。利用界面粘附力研究了聚丙烯（PP）与镍模具镶件之间的相互作用机理。结果表明，分离首先会在纳米结构的肩部发生。纳米结构和整个PP层都会被拉伸，导致脱模后平均密度急剧下降。在分离过程中，3:1纳米结构的回转半径增加最大，速度最低。纳米结构会发生变形，但整个结构仍保持良好形状。粘附能随着D/W的增加而升高。脱模力迅速增加到峰值，然后逐渐降至零。大部分力来自于界面相互作用导致的纳米结构上的粘附力和摩擦力。
