We present a nonlinear rheological characterization and supercritical carbon dioxide foaming of Olefin Block Copolymers (OBC), aiming at the investigation of the effect of polymer structure on the melt fracture and the processability. We address the challenge of obtaining reliable measurements with sample masses of the order of a milligram, in nonlinear rheological regimes and foaming processes. We selected as model system a set of three polymers that have different length of the soft blocks, ceteris paribus. The nonlinear rheological experiments and the foaming were performed with a recently developed microrheometer, μCR. The results show that, when suitable protocols and careful running conditions are chosen, nonlinear rheological behavior and foaming can be obtained with good accuracy and reproducibility. The rheological results revealed that the critical stress for the melt fracture of the OBC samples varies between 400 and 800 kPa and it is tightly connected to the molecular architecture. We found that the onset of the melt fracture in OBC increases as function of the length of the soft block. We explained that results considering the different wetting properties of the three samples. The foaming results show that it is possible to produce microcellular foams in a broad foaming window from 110 to 140∘C, and those foams have a randomly short range ordered bimodal cell size distribution that depends and can be controlled by changing the foaming temperature and the length of the soft block. This result has strong implications on the processability of the polymer, in processes such as, extrusion, injection molding and film blowing and for the manufacturing of complex hierarchical structures with photonic properties.

中文翻译：

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使用高通量实验分析烯烃嵌段共聚物发泡中的双峰电池分布


我们提出了烯烃嵌段共聚物 （OBC） 的非线性流变表征和超临界二氧化碳发泡，旨在研究聚合物结构对熔体断裂和加工性能的影响。我们解决了在非线性流变状态和发泡过程中使用一毫克量级样品质量获得可靠测量结果的挑战。我们选择了一组三种具有不同软嵌段长度的聚合物 ceteris paribus 作为模型系统。非线性流变实验和发泡是使用最近开发的微流变仪 μCR 进行的。结果表明，当选择合适的方案和仔细的运行条件时，可以获得非线性流变行为和泡沫，具有良好的准确性和可重复性。流变学结果表明，OBC 样品熔体断裂的临界应力在 400 到 800 kPa 之间变化，并且与分子结构密切相关。我们发现 OBC 中熔体断裂的发生率随着软块长度的增加而增加。我们解释了考虑了三个样品的不同润湿性能的结果。发泡结果表明，可以在 110 至 140^°C 的宽发泡窗口中生产微孔泡沫，并且这些泡沫具有随机的短距离有序双峰泡孔尺寸分布，该分布取决于并可以通过改变发泡温度和软块的长度来控制。这一结果对聚合物的加工性能、挤出、注塑和吹膜等工艺以及制造具有光子特性的复杂分层结构具有重要影响。