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In situ measurement of humidity induced changes in the refractive index and thickness of polyethylene glycol thin films

机译：原位测量湿度引起的聚乙二醇薄膜折射率和厚度的变化

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摘要

Humidity induced changes in the refractive index and thickness of polyethylene glycol (PEG) thin films are in situ determined by optical waveguide spectroscopy. PEG brushes are covalently attached to the surface of a thin gold film on a borosilicate crown glass (BK7) using a grafting-from chemical synthesis technique. The measurements are carried out in an attenuated total internal reflection setup. At low humidity levels, both the refractive index and the thickness change gradually due to swelling of the PEG thin films upon water intake. At around 80% relative humidity, a steep decrease in the refractive index and a steep increase in the thickness are observed as a result of a phase change from a semicrystalline state to a physical gel state. The hydrogenation of PEG films causes a less pronounced phase change from a semicrystalline state to a gel state. Due to fewer ether oxygen atoms available for the water molecules to make hydrogen bonding, the polymer has a more stable structure than before and the phase change is observed to shift to higher humidity levels. It is discussed that such a humidity induced change in the index of refraction can be utilized in constructing of a PEG based humidity sensor.
机译：湿度引起的聚乙二醇（PEG）薄膜的折射率和厚度变化是通过光波导光谱法原位确定的。使用化学合成接枝技术将PEG刷共价附着在硼硅酸盐冠玻璃（BK7）上的金薄膜表面上。测量是在衰减的全内反射设置中进行的。在低湿度下，由于吸水时PEG薄膜的溶胀，折射率和厚度都逐渐变化。在约80％的相对湿度下，由于从半晶态到物理凝胶态的相变，观察到折射率的急剧下降和厚度的急剧上升。 PEG膜的氢化导致从半晶态到凝胶态的相变不太明显。由于较少的醚氧原子可用于水分子形成氢键，因此该聚合物的结构比以前更稳定，并且观察到相变会移至更高的湿度水平。讨论了这样的湿度引起的折射率变化可以用于构建基于PEG的湿度传感器。

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