Liu Shanqiu, de Beer Sissi, Batenburg Kevin M, Gojzewski Hubert, Duvigneau Joost, Vancso G Julius
Materials Science and Technology of Polymers, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, the Netherlands.
ACS Appl Mater Interfaces. 2021 Apr 14;13(14):17034-17045. doi: 10.1021/acsami.1c00569. Epub 2021 Mar 30.
The interface between nucleating agents and polymers plays a pivotal role in heterogeneous cell nucleation in polymer foaming. We describe how interfacial engineering of nucleating particles by polymer shells impacts cell nucleation efficiency in CO blown polymer foams. Core-shell nanoparticles (NPs) with a 80 nm silica core and various polymer shells including polystyrene (PS), poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), and poly(acrylonitrile) (PAN) are prepared and used as heterogeneous nucleation agents to obtain CO blown PMMA and PS micro- and nanocellular foams. Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy are employed to confirm the successful synthesis of core-shell NPs. The cell size and cell density are determined by scanning electron microscopy. Silica NPs grafted with a thin PDMS shell layer exhibit the highest nucleation efficiency values, followed by PAN. The nucleation efficiency of PS- and PMMA-grafted NPs are comparable with the untreated particles and are significantly lower when compared to PDMS and PAN shells. Molecular dynamics simulations (MDS) are employed to better understand CO absorption and nucleation, in particular to study the impact of interfacial properties and CO-philicity. The MDS results show that the incompatibility between particle shell layers and the polymer matrix results in immiscibility at the interface area, which leads to a local accumulation of CO at the interfaces. Elevated CO concentrations at the interfaces combined with the high interfacial tension (caused by the immiscibility) induce an energetically favorable cell nucleation process. These findings emphasize the importance of interfacial effects on cell nucleation and provide guidance for designing new, highly efficient nucleation agents in nanocellular polymer foaming.
成核剂与聚合物之间的界面在聚合物发泡的异质泡孔成核过程中起着关键作用。我们描述了通过聚合物壳层对成核颗粒进行界面工程设计如何影响CO₂吹塑聚合物泡沫中的泡孔成核效率。制备了具有80 nm二氧化硅核以及包括聚苯乙烯（PS）、聚二甲基硅氧烷（PDMS）、聚甲基丙烯酸甲酯（PMMA）和聚丙烯腈（PAN）等各种聚合物壳层的核壳纳米颗粒（NPs），并将其用作异质成核剂，以制备CO₂吹塑的PMMA和PS微孔及纳米孔泡沫。采用傅里叶变换红外光谱、热重分析和透射电子显微镜来确认核壳NPs的成功合成。通过扫描电子显微镜确定泡孔尺寸和泡孔密度。接枝有薄PDMS壳层的二氧化硅NPs表现出最高的成核效率值，其次是PAN。接枝PS和PMMA的NPs的成核效率与未处理的颗粒相当，与PDMS和PAN壳层相比显著更低。采用分子动力学模拟（MDS）来更好地理解CO₂吸收和成核过程，特别是研究界面性质和CO₂亲合性的影响。MDS结果表明，颗粒壳层与聚合物基体之间的不相容性导致界面区域的不混溶，从而导致CO₂在界面处局部积累。界面处升高的CO₂浓度与高界面张力（由不混溶性引起）共同诱导了一个能量上有利的泡孔成核过程。这些发现强调了界面效应在泡孔成核中的重要性，并为在纳米孔聚合物发泡中设计新型高效成核剂提供了指导。
