Bai Lian, Sharma Radhika, Cheng Xiang, Macosko Christopher W
Department of Chemical Engineering and Materials Science, University of Minnesota , 421 Washington Ave. SE, Minneapolis, Minnesota 55455, United States.
Langmuir. 2018 Jan 23;34(3):1073-1083. doi: 10.1021/acs.langmuir.7b03085. Epub 2017 Oct 30.
Selective localization of graphene in co-continuous polymer blends is an attractive method for preparing conductive polymer composites. Localization of graphene at the interface between the two polymer phases produces good conductivity at ultra-low concentrations. Although graphene localization is ultimately dependent on thermodynamic factors such as the surface energy of graphene and the two polymer components, kinetics also strongly affects the migration and localization of graphene in polymer blends during melt compounding. However, few studies have systemically investigated the important role of kinetics on graphene localization. Here, we introduced graphene nanoplatelets (GNPs) in polylactic acid (PLA)/polystyrene (PS) co-continuous polymer blends. Although GNPs in thermal equilibrium prefer the PS phase, we were able to kinetically trap GNPs at the interface of polymer blends via control of melt-compounding sequences, mixing times and shear rates. Utilizing morphological, rheological, and electrical measurements, we verified graphene localization and the suppression of coarsening in co-continuous polymer blends during annealing. When GNPs were premixed with the thermodynamically less-favorable PLA phase before mixing with the PS phase, GNPs can be kinetically trapped at the interface during melt compounding. Moreover, we show that a shorter melt-compounding time gives rise to a higher GNP interfacial coverage and a more effective morphology stabilization effect. Blends with as low as 0.5 wt % GNPs with only 30 s of melt compounding have a room-temperature conductivity of ∼10 S/cm, which is larger than blends with longer melt-compounding times and potentially useful for antistatic materials. The in-depth study on the kinetics of graphene localization in our work provides a general guideline for the kinetic control of the localization of platelike nanofillers in polymer blends. Our study also demonstrates a facile method for manufacturing conductive polymer blends with low percolation thresholds.
在互穿聚合物共混物中选择性地定位石墨烯是制备导电聚合物复合材料的一种有吸引力的方法。石墨烯在两个聚合物相之间的界面处定位能够在超低浓度下产生良好的导电性。尽管石墨烯的定位最终取决于热力学因素，如石墨烯和两种聚合物组分的表面能，但动力学在熔体共混过程中对石墨烯在聚合物共混物中的迁移和定位也有很大影响。然而，很少有研究系统地研究动力学对石墨烯定位的重要作用。在这里，我们将石墨烯纳米片（GNPs）引入聚乳酸（PLA）/聚苯乙烯（PS）互穿聚合物共混物中。尽管处于热平衡状态的GNPs更倾向于PS相，但我们能够通过控制熔体共混顺序、混合时间和剪切速率，在动力学上使GNPs捕获在聚合物共混物的界面处。利用形态学、流变学和电学测量，我们验证了在退火过程中互穿聚合物共混物中石墨烯的定位以及粗化的抑制。当GNPs在与PS相混合之前先与热力学上不太有利的PLA相预混合时，GNPs在熔体共混过程中可以在动力学上捕获在界面处。此外，我们表明较短的熔体共混时间会导致更高的GNP界面覆盖率和更有效的形态稳定效果。仅经过30秒熔体共混的含0.5 wt % GNPs的共混物在室温下的电导率约为10 S/cm，这比熔体共混时间更长的共混物的电导率更高，并且可能对抗静电材料有用。我们工作中对石墨烯定位动力学的深入研究为动力学控制聚合物共混物中片状纳米填料的定位提供了一般指导原则。我们的研究还展示了一种制造具有低渗滤阈值的导电聚合物共混物的简便方法。
