Heterogeneous Nucleation of High-Density Polyethylene Crystals on Graphene within Microdomains
Heterogeneous Nucleation of High-Density Polyethylene Crystals on Graphene within Microdomains
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DOI：
10.1021/acs.macromol.3c00342
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发表时间：
2023-05-15
期刊：
影响因子：
5.5
通讯作者：
Rutledge，Gregory C. C.
中科院分区：
文献类型：
--
作者：
Volchko，Nathan W. W.;Rutledge，Gregory C. C.
在聚合物过程中，成核剂通常用于控制结晶动力学，但它们的应用在很大程度上仍然是一个试验和错误的问题。热力学上，成核剂的效率可以通过底物/晶体、晶体/熔体和底物/熔体界面能的差异来量化，Δσ。本文研究了石墨烯纳米片（GNP）作为高密度聚乙烯（HDPE）成核剂的效率。HDPE成核和结晶速度很快，因此Δσ在实验中特别难以测量。为了克服这一困难，将HDPE+GNP的共混物限制在微畴内，使结晶受到成核限制。采用了两种微畴形成方法。首先，HDPE+GNP与不混相的聚苯乙烯（PS）基体熔融共混，并用差示扫描量热法（DSC）对结晶进行表征；第二步，将HDPE+GNP在甲苯中的分散体喷射到PS基片上，并利用偏光显微镜（POM）对其结晶进行了表征。用这两种方法测量了几种结晶温度和几种GNP负载下的非均相成核率，发现在GNP负载下的非均相成核率非常一致。计算出HDPE+GNP的Δσ值为0.83±0.18 erg/cm2。该值仅比HDPE纤维（一种几乎理想的HDPE成核剂）上非均质成核的HDPE大2.8倍，比其他聚合物中许多最佳成核剂小得多。我们认为GNP是一种高效的HDPE成核剂。
In polymer processes, nucleating agents are often used to control the kinetics of crystallization, but their application remains largely a matter of trial and error. Thermodynamically, the efficiency of a nucleating agent can be quantified by the difference in substrate/crystal, crystal/melt, and substrate/melt interfacial energies, Δσ. In this work, the efficiency of graphene nanoplatelets (GNP) as nucleating agents for high-density polyethylene (HDPE) is investigated. HDPE nucleates and crystallizes rapidly, so Δσ can be especially difficult to measure experimentally. To overcome this difficulty, blends of HDPE+GNP are confined to microdomains so that crystallization becomes nucleation limited. Two methods of microdomain formation are employed. In the first, HDPE+GNP is melt-blended with an immiscible matrix of polystyrene (PS), and crystallization is characterized using differential scanning calorimetry (DSC); in the second, dispersions of HDPE+GNP in toluene are sprayed onto PS substrates, and crystallization is characterized with polarized optical microscopy (POM). Heterogeneous nucleation rates at several crystallization temperatures and for several GNP loadings were measured by these two methods and found to give excellent agreement across GNP loadings. The value of Δσ for HDPE+GNP is calculated to be 0.83 ± 0.18 erg/cm2. This value is only 2.8 times larger than that reported for HDPE nucleated heterogeneously on a HDPE fiber, a nearly ideal nucleating agent for HDPE, and much smaller than many of the best nucleating agents reported for other polymers. We conclude that GNP is an efficient nucleating agent for HDPE.