Hagen David A, Saucier Lauren, Grunlan Jaime C
Department of Mechanical Engineering, Texas A&M University , College Station, Texas 77843, United States.
ACS Appl Mater Interfaces. 2014 Dec 24;6(24):22914-9. doi: 10.1021/am507603z. Epub 2014 Dec 15.
Polymer-clay thin films constructed via layer-by-layer (LbL) assembly, with a nanobrick wall structure (i.e., clay nanoplatelets as bricks surrounded by a polyelectrolyte mortar), are known to exhibit a high oxygen barrier. Further barrier improvement can be achieved by lowering the pH of the clay suspension in the polyethylenimine (PEI) and montmorillonite (MMT) system. In this case, the charge of the deposited PEI layer is increased in the clay suspension environment, which causes more clay to be deposited. At pH 4, MMT platelets deposit with near perfect ordering, observed with transmission electron microscopy, enabling a 5× improvement in the gas barrier for a 10 PEI/MMT bilayer thin film (85 nm) relative to the same film made with pH 10 MMT. This improved gas barrier approaches that achieved with much higher aspect ratio vermiculite clay. In essence, lower pH is generating a higher effective aspect ratio for MMT due to greater induced surface charge in the PEI layers, which causes heavier clay deposition. These flexible, transparent nanocoatings have a wide range of possible applications, from food and electronics packaging to pressurized bladders.
通过层层（LbL）组装构建的具有纳米砖壁结构（即粘土纳米片作为砖块，被聚电解质灰浆包围）的聚合物 - 粘土薄膜，已知具有高氧气阻隔性。通过降低聚乙烯亚胺（PEI）和蒙脱石（MMT）体系中粘土悬浮液的pH值，可以进一步提高阻隔性能。在这种情况下，在粘土悬浮液环境中，沉积的PEI层的电荷增加，这导致更多的粘土沉积。在pH值为4时，用透射电子显微镜观察到蒙脱石薄片以近乎完美的有序方式沉积，对于10层PEI/MMT双层薄膜（85纳米），相对于用pH值为10的蒙脱石制成的相同薄膜，其气体阻隔性能提高了5倍。这种改进的气体阻隔性能接近用高得多的纵横比蛭石粘土所实现的性能。本质上，较低的pH值由于PEI层中更大的诱导表面电荷而为蒙脱石产生了更高的有效纵横比，这导致更重的粘土沉积。这些柔性、透明的纳米涂层具有广泛的可能应用，从食品和电子包装到加压气囊。
