Tazreiter Martin, Christian Paul, Schennach Robert, Grießer Thomas, Coclite Anna Maria
Institute of Solid State Physics , NAWI Graz , Graz University of Technology , 8010 Graz , Austria . Email:
Department Kunststofftechnik , Montanuniversität Leoben , 8700 Leoben , Austria.
Anal Methods. 2017 Sep 28;9(36):5266-5273. doi: 10.1039/c7ay01748k. Epub 2017 Aug 21.
The chemical composition of a copolymer drives many important material properties and quantification in terms of comonomer volume fraction is thus of practical relevance for many studies. Infrared spectroscopy is one of the most common techniques for compositional analysis but it usually relies on manual evaluation of baselines and peak heights, which can be rather inaccurate and become a laborious task when having multiple spectra to evaluate. On the contrary, Maxwell's theory of electrodynamics can be used to calculate the complex index of refraction from measured spectra promising a more accurate quantification. Since this procedure is rather involved, we propose a simple in-house developed IR-quantification routine to automatically evaluate the comonomer volume fractions of thin copolymer films by using the Bouguer-Lambert-Beer approximation after correcting the baseline of all absorbance spectra automatically. This method was experimentally evaluated on over 40 thin polymeric coatings synthesized by initiated chemical vapor deposition on silicon substrates. The samples comprised a wide range of different compositions and were synthesized from four different monomers, with single films consisting of up to three components. All data obtained by our routine was compared with data from spectroscopic ellipsometry and with X-ray photoelectron spectroscopy data of selected samples. The comparisons show that the IR-quantification routine reliably evaluated the polymer composition even when the involved comonomers exhibited similar chemistry, as it is the case for methacrylic acid cross-linked with ethylene glycol dimethacrylate.
共聚物的化学组成决定了许多重要的材料性能，因此根据共聚单体体积分数进行定量分析对于许多研究具有实际意义。红外光谱法是成分分析最常用的技术之一，但它通常依赖于对基线和峰高的人工评估，这可能相当不准确，并且在评估多个光谱时会成为一项繁琐的任务。相反，麦克斯韦电动力学理论可用于根据测量光谱计算复折射率，有望实现更准确的定量分析。由于这个过程相当复杂，我们提出了一种简单的自行开发的红外定量程序，通过在自动校正所有吸收光谱的基线后使用布格-朗伯-比尔近似法来自动评估共聚物薄膜的共聚单体体积分数。该方法在通过引发化学气相沉积在硅衬底上合成的40多种聚合物薄膜涂层上进行了实验评估。样品包含广泛的不同组成，由四种不同的单体合成，单膜最多由三种成分组成。我们程序获得的所有数据与光谱椭偏仪的数据以及选定样品的X射线光电子能谱数据进行了比较。比较结果表明，即使所涉及的共聚单体具有相似的化学性质，如甲基丙烯酸与乙二醇二甲基丙烯酸酯交联的情况，红外定量程序也能可靠地评估聚合物组成。
