基于近红外光谱的柔性基底紫外臭氧改性效果表征研究

近年来，随着纳米科技、聚合物材料和先进制造技术的发展，以柔性传感器为代表的新兴柔性电子器件在可穿戴、健康医疗、物联网终端等领域发挥着越来越重要的作用。作为柔性电子器件的载体，柔性基底对传感器的机械可靠性和电学传感性能等方面有着重要的意义。但由于其表面非极性键造成的高疏水性限制了功能性材料在其表面的沉积，常常造成柔性基底层与电极层/敏感层之间不稳定的界面结合。因此，利用紫外臭氧处理对柔性基底表面改性受到了广泛的关注。利用近红外光谱技术对柔性基底的紫外臭氧处理效果进行快速精准评估，旨在从基团分子层面探究其改性效果，在实际应用中是对传统依靠接触角测量评估方法的有效补充。具体而言，对四种常见的柔性基底材料聚二甲基硅氧烷(PDMS)、聚萘二甲酸乙二醇酯（PEN）、聚对苯二甲酸乙二醇酯（PET）和聚酰亚胺（PI）进行了1/2/5/10 min不同时长的紫外臭氧（UVO）改性处理，并利用近红外光谱对其改性效果进行表征研究，最后利用接触角测量方法对上述的表征结果进行了验证分析。近红外光谱分析表明：对于柔性PDMS基底，紫外光能量不足以切断其中的甲基（—CH₃）官能团和（—C—Si—）等化学键，无法引入羟基、羧基等亲水性基团。对于柔性PEN和PET基底而言，紫外臭氧处理的效果要优于柔性PDMS基底，且对柔性PET基底的处理效果要优于柔性PEN基底，其原因可能是PEN基底材料中萘环的双环结构具有很强的紫外光吸收能力，阻隔了380 nm以下的大部分紫外线能量。对于柔性PI基底，紫外臭氧处理可以有效引入羟基（—OH）和羧基（—COOH）等活性基团，且这些官能团的强度和数量随着处理时间的增加而增加，从而在短时间内使得PI基底表面能增大、接触角减小、湿润性提高。接触角测试结果验证：紫外臭氧处理对于柔性PDMS基底处理效果不明显（接触角下降幅度为8.4%）；对柔性PET基底处理的效果（接触角下降幅度为39.6%）要优于柔性PEN基底的处理效果（接触角下降幅度为9.4%）；紫外臭氧处理的效果对柔性PI基底处理效果最佳，接触角下降幅度达到了62.7%。

Infrared Spectral Characterization of Ultraviolet Ozone Treatment on Substrate Surface for Flexible Electronics

In recent years, with the progress of nanotechnology, polymer materials and advanced manufacturing technology, emerging flexible electronic devices represented by flexible sensors are playing an increasingly important role in the fields of wearable, healthcare, Internet of Things terminal and so on. As the carrier of flexible electronic devices, the flexible substrates are of great significance to the mechanical reliability and electrical sensing performance of sensors. However, the high hydrophobicity caused by the dominant non-polar bonds on the flexible substrate surface restricts the deposition of functional materials on the surface, which results in the unstable interfacial bond between the substrate and the electrode＼sensitive layer. Therefore, the surface modification of flexible substrates by ultraviolet-ozone (UVO) treatment has received extensive attention. In this study, we explored the rapid and accurate evaluation of the UVO treatment effect of the flexible substrate by near infrared (NIR) spectroscopy, aiming to characterize the modification effect from the level of group and molecule, which is an effective supplement to the contact angle measurement method. In particular, four kinds of flexible substrates, polydimethylsiloxane (PDMS), polyethylene terephthalate (PEN), polyethylene terephthalate (PET) and polyimide (PI) were modified by 1/2/5/10 minutes with UVO treatment, and the modification effects were characterized by NIR spectroscopy. Finally, the characterization analysis results were verified by the contact angle measurement. The NIR spectrum analysis showed that the UV energy was not enough to break the methyl (—CH₃) functional group and (O—Si—O) chemical bond in the flexible PDMS substrate, so the hydrophilic groups such as hydroxyl group and carboxyl group could not be introduced. For flexible PEN and PET substrates, the treatment effect of UVO was better than that of flexible PDMS substrates, and the treatment effect of flexible PET substrates was better than that of flexible PEN substrates. The reason may be that the naphthalene ring double-ring structure in the PEN substrate has a strong ultraviolet light absorption ability, which blocks most ultraviolet energy below 380 nm. For flexible PI substrates, UVO treatment can effectively introduce active groups such as hydroxyl (C—OH) and carboxylic acid (OC═O), and the strength and number of these functional groups increase with the increase of modification time, so that the surface energy of PI substrates increases in a short time, the contact Angle decreases, and the wettability improves. The contact angle measurement results showed that the UVO treatment had no obvious effect on the flexible PDMS substrate (the contact angle decreased by 8.4%). The modification effect of flexible PET substrate (39.6% contact angle decline) was better than that of flexible PEN substrate (9.4% contact angle decline). UVO treatment was the most effective for the flexible PI substrate, since the contact angle decreased by 62.7%.