Analysis of automotive paints by ATR FT-IR microspectroscopy

ATR FT-IR microspectroscopy is used to analyze and identify the automotive paints. Three types of automotive paints including paint chips of different colors and shades, multilayer automotive paints, and thin trace smear on automotive paint were characterized by ATR FT-IR microspectroscopy. Two homemade [micro]ATR accessories; the slide-on diamond [micro]IRE and the slide-on Ge [micro]IRE, using an infrared microscope were employed for surface characterization of automotive paints. The spectra acquired by the slide-on diamond [micro]IRE and the slide-on Ge [micro]IRE were similar to those acquired by conventional ATR technique. The spectra from different colors and shades of paint show different spectral features due to the difference in compositions such as binder, pigment, and additive. Due to small contact area of the slide-on diamond [micro]IRE and slide-on Ge [micro]IRE, an individual layer of the multilayered automotive paints can be selectively analyzed without layer separation changing in chemical composition in each small sampling position can be analyzed. In additional, paints with the same colors but different chemical composition can be identified by surface line mapping. Thin trace smear were analyzed directly without interference from paint support by the slide-on Ge [micro]IRE. The slide-on diamond [micro]IRE and the slide-on Ge [micro]IRE were suitable for forensic analysis of automotive paint because of their small contact area and good contact with the sample. The technique is non-destructive, has short analysis time, can be performed without a sample preparation.

本研究采用衰减全反射傅里叶变换红外显微光谱（ATR FT-IR microspectroscopy）技术开展汽车涂料的分析与鉴别工作。本次实验对三类汽车涂料样品进行了表征，分别为不同颜色与色阶的涂料碎屑、多层结构汽车涂料，以及附着于汽车涂料表面的微量痕迹涂膜。实验采用两套自制[显微]ATR附件——贴合式金刚石[显微]内反射元件（slide-on diamond [micro]IRE）与贴合式锗[显微]内反射元件（slide-on Ge [micro]IRE），搭配红外显微镜完成汽车涂料的表面表征测试。通过上述两款附件采集得到的红外光谱，与常规ATR技术获取的光谱结果具有高度一致性。不同颜色与色阶的涂料样品，因其基料、颜料与助剂等组分存在差异，呈现出各不相同的光谱特征。由于贴合式金刚石[显微]内反射元件与贴合式锗[显微]内反射元件的接触面积较小，可对多层汽车涂料的单一层面进行选择性分析，无需进行分层处理，且可在每个微小采样点位精准分析其化学成分变化。此外，对于颜色一致但化学成分存在差异的涂料样品，可通过表面线扫描成像技术实现有效鉴别。采用贴合式锗[显微]内反射元件可直接对微量痕迹涂膜进行分析，不会受到涂料载体的信号干扰。鉴于上述两款附件接触面积小、与样品贴合效果优异，二者均适用于汽车涂料的法医鉴定分析。该技术具备无损检测、分析耗时短、无需样品前处理的显著优势。