Department of Photochemistry, University of Haute Alsace, Ecole Nationale Supérieure de Chimie de Mulhouse, 3 rue Alfred Werner, 68093 Mulhouse Cedex, France.
Appl Spectrosc. 2011 Oct;65(10):1126-32. doi: 10.1366/11-06299.
The depth characterization of photopolymer films by confocal Raman microscopy is often troublesome due to refraction effects. To minimize these effects, we used an oil immersion objective and a method was developed to avoid penetration of the oil without damaging the sample surface. Since the surface may be sticky if oxygen in the air inhibits the photopolymerization, a protective layer could not be put onto the film. Therefore, the method consists in using a thin polypropylene foil as substrate for the coating and placing the sample upside down under the objective. In this manner, the immersion oil could be deposited on top of the polypropylene. The advantage of this setup is that the oil, polypropylene substrate, and photopolymer film have close refractive indices. Basic calculations showed that the depth resolution is hardly affected in that configuration and double-bond conversion profiles could be plotted as a function of reliable nominal depth. The validity of the methodology was confirmed by experiments carried out with a dry metallurgical objective on the sample surface, face up, where refraction effects are still minor. In addition, infrared spectroscopy, which was used to follow the photopolymerization, corroborated the Raman conversion of the films over their thickness. The confocal Raman microscopy method can be applied to various photopolymerized systems to characterize their behavior towards oxygen inhibition and other heterogeneities in conversion arising from inner filter effects or interactions between additives for instance.
由于折射效应，使用共焦拉曼显微镜对光聚合薄膜进行深度特性描述往往比较麻烦。为了最小化这些影响，我们使用了油浸物镜，并开发了一种方法来避免油的渗透而又不损坏样品表面。由于如果空气中的氧气抑制光聚合作用，表面可能会发粘，因此不能在薄膜上添加保护层。因此，该方法包括使用薄的聚丙烯箔作为涂层的基底，并将样品倒置放在物镜下。这样，浸油就可以沉积在聚丙烯的顶部。这种设置的优点是油、聚丙烯基底和光聚合薄膜具有相近的折射率。基本计算表明，在这种配置下，深度分辨率几乎不受影响，并且可以根据可靠的标称深度绘制双键转化率曲线。该方法的有效性通过在样品表面上使用干燥的金相物镜进行的实验得到了验证，在那里折射效应仍然较小。此外，用于跟踪光聚合的红外光谱证实了薄膜在其厚度上的拉曼转换。共焦拉曼显微镜方法可以应用于各种光聚合体系，以表征它们对氧气抑制的行为以及由于内滤效应或添加剂之间的相互作用等引起的转化率中的其他不均匀性。
