Department of Polymer Engineering, University of Akron , Akron, Ohio 44325, United States.
Langmuir. 2016 Jun 21;32(24):6020-7. doi: 10.1021/acs.langmuir.6b00206. Epub 2016 Jun 7.
Weak polyelectrolyte multilayers (PEMs) prepared by the layer-by-layer technique have attracted a great deal of attention as smart responsive materials for biological and other applications in aqueous medium, but their dynamic behavior as a function of exposure to a wide temperature range is still not well understood. In this work, the thermally dependent swelling behavior of PEMs consisting of branched poly(ethylenimine) and poly(acrylic acid) is studied by temperature controlled in situ spectroscopic ellipsometry. Because of diffusion and interpenetration of polyelectrolytes during film deposition, the PEMs densify with increasing bilayer number, which further affects their water uptake behavior. Upon heating to temperatures below 60 °C, the worsened solvent quality of the PEM in water causes deswelling of the PEMs. However, once heated above this critical temperature, the hydrogen bonds within the PEMs are weakened, which allows for chain rearrangement within the film upon cooling, resulting in enhanced water uptake and increased film thickness. The current work provides fundamental insight into the unique dynamic behavior of weak polyelectrolyte multilayers in water at elevated temperatures.
弱聚电解质多层膜（PEMs）通过层层技术制备，作为智能响应材料，在水介质中具有很大的应用潜力，例如生物方面的应用，但它们在宽温度范围内的动态行为仍然不太清楚。在这项工作中，通过温度控制原位椭圆偏光光谱法研究了由支化聚（乙二胺）和聚（丙烯酸）组成的 PEMs 的热膨胀行为。由于在薄膜沉积过程中聚电解质的扩散和互穿，随着双层数的增加，PEMs 变得更加致密，这进一步影响了它们的吸水性。在加热到 60°C 以下的温度时，PEM 在水中的溶剂质量变差会导致 PEM 溶胀。然而，一旦加热到这个临界温度以上，PEM 内的氢键就会减弱，这使得链在薄膜内重新排列，从而增加水的吸收和薄膜厚度。目前的工作为了解高温下水环境中弱聚电解质多层膜的独特动态行为提供了基础。
