We used molecular dynamics (MD) simulation to investigate whether an environmental stress cracking (ESC) agent would help the cavitation process in linear polyethylene (LPE) and branched polyethylene (BPE) by examining the free volume hole size and spatial distributions at the [PE]-[ESC agent] interfaces. The BPE models used contained 10 and 82 butyl/hexyl branches/1000 backbone carbons and the ESC agent used was nonyl ethoxylate (NE) at concentrations 0.001–1.4 $wt\%$. The results show that there exist no significant changes in the packings of LPE and BPE chains, as characterized by their radial distribution functions (RDFs), in the presence of NE regardless its concentration. However, molecular packings at the [PE]-[NE] interfaces vary with NE concentration. In particular, ethylene (E) segments of NE, compared to the ethylene oxide (EO) segments, exhibit stronger association with LPE and BPE chains. We used the Voronoi tessellation method to determine the size and spatial distributions of free volume holes at the [PE]-[NE] interfaces and found that more and larger free volume holes formed around the E-segments than the EO-segments. And such effect was found to be more pronounced in the case of LPE chains than the BPE chains. We further investigated the free volume holes coalescence dynamics using the Fourier mode analysis. The number of frequency modes and the corresponding intensities of the E-segments were significantly higher than those of EO-segments, suggesting that E-segments exhibited a higher tendency to form more and larger free volume holes. This suggests that [PE]-[E-segments] interfaces have a higher chance to form larger voids (i.e., cavitation, a feature of brittle failure that is experimentally observed in ESC). The tendency intensified with increasing NE concentration but was reduced by the presence of short chain branches. The high mobility of terminal carbons in the short chain branches is believed to suppress the formation of large free volume holes at the [PE]-[E-segments] interfaces by absorbing the newly formed free volume by that of the terminal carbons.

我们使用分子动力学 (MD) 模拟来研究环境应力开裂 (ESC) 剂是否有助于线性聚乙烯 (LPE) 和支化聚乙烯 (BPE) 的空化过程，方法是检查 [PE] 处的自由体积孔尺寸和空间分布]-[ESC代理]接口。使用的 BPE 模型包含 10 和 82 个丁基/己基支链/1000 个主链碳，使用的 ESC 试剂是壬基乙氧基化物 (NE)，浓度为 0.001–1.4$w吨\%$. 结果表明，在存在 NE 的情况下，无论其浓度如何，LPE 和 BPE 链的堆积都没有显着变化，其特征在于它们的径向分布函数 (RDF)。然而，[PE]-[NE] 界面处的分子堆积随 NE 浓度而变化。特别是，与环氧乙烷 (EO) 链段相比，NE 的乙烯 (E) 链段与 LPE 和 BPE 链表现出更强的结合。我们使用 Voronoi 镶嵌方法确定 [PE]-[NE] 界面处自由体积孔的大小和空间分布，发现 E 段周围形成的自由体积孔比 EO 段更多和更大。并且发现这种效果在 LPE 链的情况下比 BPE 链更明显。我们使用傅立叶模式分析进一步研究了自由体积孔聚结动力学。E段的频率模式数量和相应的强度明显高于EO段，表明E段表现出形成更多更大自由体积孔的更高趋势。这表明 [PE]-[E 段] 界面更有可能形成更大的空隙（即空化，一种在 ESC 中通过实验观察到的脆性破坏特征）。这种趋势随着 NE 浓度的增加而增强，但由于短支链的存在而减弱。