Guan Ying, Yang Shuguang, Zhang Yongjun, Xu Jian, Han Charles C, Kotov Nicholas A
State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China.
J Phys Chem B. 2006 Jul 13;110(27):13484-90. doi: 10.1021/jp061548g.
We observed Fabry-Perot fringes in the absorption spectra of hydrogen-bonded layer-by-layer (LBL) films of poly(vinyl pyrrolidone) (PVPON) and poly(acrylic acid) (PAA), which stem from the interferences between beams transmitted and partially reflected at the highly smooth film-air interface and film-quartz interface. The appearance and disappearance of Fabry-Perot fringes can be used to evaluate the homogeneity of the film. They also provide information about the film thickness. Using this optical phenomenon, with a minimal requirement of instrumentation, we studied the effect of several experimental conditions on the film buildup and structure. The film grows linearly with dipping cycles. Films fabricated from higher molecular weight polymers tend to be thicker. Increasing the concentration of the assembly solutions can also make thicker films. However, films from high molecular weight polymers or high concentration assembly solutions may be heterogeneous and do not display Fabry-Perot fringes in their absorption spectra. The defects in these heterogeneous films can be healed by a postannealing in water or diluted HCl to allow the chain rearrangement to complete. We further found the PVPON/PAA films can be eroded by long-term annealing in water or diluted HCl by monitoring the movement of the Fabry-Perot fringes. In most cases, the erosion rate is constant with annealing time. The erosion rate decreases with a decrease in the pH of the media and an increase in the molecular weight of the polymers.
我们在聚乙烯吡咯烷酮（PVPON）和聚丙烯酸（PAA）的氢键层层（LBL）薄膜的吸收光谱中观察到了法布里-珀罗条纹，这是由在高度光滑的薄膜-空气界面和薄膜-石英界面处透射和部分反射的光束之间的干涉引起的。法布里-珀罗条纹的出现和消失可用于评估薄膜的均匀性。它们还提供了有关薄膜厚度的信息。利用这种光学现象，在对仪器要求最低的情况下，我们研究了几种实验条件对薄膜形成和结构的影响。薄膜随浸渍循环呈线性生长。由高分子量聚合物制成的薄膜往往更厚。提高组装溶液的浓度也可以使薄膜更厚。然而，由高分子量聚合物或高浓度组装溶液制成的薄膜可能不均匀，并且在其吸收光谱中不显示法布里-珀罗条纹。这些不均匀薄膜中的缺陷可以通过在水中或稀盐酸中进行后退火来修复，以使链重排完成。通过监测法布里-珀罗条纹的移动，我们进一步发现PVPON/PAA薄膜可以通过在水中或稀盐酸中长时间退火而被侵蚀。在大多数情况下，侵蚀速率随退火时间恒定。侵蚀速率随介质pH值的降低和聚合物分子量的增加而降低。
