Studies of polymer-surface nitrogenation using dielectric-barrier postdischarges (“NitroPol”)

聚合物表面的等离子体氮化最近在诸如增强附着力、化学金属沉积或生物医学用途等应用中获得了很大的兴趣，举几个重要的例子。等离子体氮化聚合物表面与等离子体氧化聚合物表面的不同之处在于它们的碱性和亲核性，这是由带有未成键电子对的n官能团引入的，而含氧聚合物表面通常是酸性和亲电的。尽管等离子体氮化聚合物表面很重要，但目前对用氮气或含氮气体对聚合物表面进行等离子体处理的了解远不如氧气或空气等离子体处理先进。在这里提出的项目中，大气压DBDs在N2中的主要研究方向是它们与聚烯烃表面和模型化合物的相互作用。首先，这些研究应利用N2介质阻挡放电提供的流动后排放物，作为活性物质的来源，这些活性物质应该在表面修饰中起主导作用。本项目旨在根据主要涉及基态和亚稳态激发原子N（4S）和N（2P）以及亚稳态激发分子N2(A)的气相密度，鉴定上述相互作用的产物，即引入聚合物表面的官能团，以及产物形成的机理和动力学。通过光学发射光谱和化学动力学计算，可以很准确地确定密度。为了分析表面，将使用衰减反射模式的傅里叶变换红外光谱或浸没-红外反射-吸收光谱，以及x射线光电子光谱。还将使用化学衍生化和捕获技术对产品进行分类和量化，并稳定不稳定的部分。模型烷烃实验还将通过气相色谱法和高分辨率质谱法进行评估。本项目的科学目标是回答三个基本问题：(1)常压余辉氮化后聚烯烃表面的确切化学性质是什么，形成了什么样的官能团？(2)有哪些气相物质参与了特定官能团的形成，是否有一个合理的化学途径可以证明它的形成，并与最先进的化学机制知识相一致？(3)生成物的生成速率如何依赖于物种密度，能否形成一套速率方程？从更实用的等离子体表面技术的角度来看，该项目将提供放电和放电后参数的精确描述，以获得具有众所周知的含氮官能团的聚烯烃的可控表面改性。

Plasma-nitrogenation of polymer surfaces has recently gained much interest for applications such as adhesion enhancement, electroless metal deposition, or biomedical purposes, to name important examples. Plasma-nitrogenated polymer surfaces differ from plasma-oxidized ones by their basiscity and nucleophilicity, introduced by N-functional groups with unbonded electron pairs, while oxygen-containing polymer surfaces generally are acidic and electrophilic. In spite of the importance of plasma-nitrogenated polymer surfaces the current understanding regarding plasma treatment of polymer surfaces with nitrogen or nitrogen-containing gases is much less advanced than that of oxygen- or air-plasma treatment. In the project proposed here, atmospheric-pressure DBDs in N2 shall primarily be studied with respect to their interaction with polyolefin surfaces and with model compounds. In the first place these investigations shall be performed utilizing flowing postdischarges fed by dielectric-barrier discharges in N2, serving as sources of active species which are supposed to play a dominant role for the surface modification. The project aims at the identification of products of the mentioned interaction, i. e., functional groups introduced to the polymer surface, as well as on mechanism and kinetics of the product formation, based on gas-phase densities of reactive species mainly involved: groundstate and metastable excited atoms, N(4S) and N(2P), and metastable excited molecules, N2(A). The densities can be determined with sufficient accuracy from optical emission spectroscopy and chemical-kinetic calculations. To analyze the surfaces, Fourier-transform infrared spectroscopy in the attenuated reflection mode or immersion-IRRAS (infrared reflexion-absorption spectroscopy) will be applied, as well as X-ray photoelectrons spectroscopy. Use will also be made of chemical-derivatization and trapping techniques to classify and quantify products and to stabilize labile moieties. Experiments with model alkanes will additionally be evaluated by gas chromatography coupled with high-resolution mass spectrometry. Scientific objectives of this project are the answers to three fundamental questions: (1) What is the exact chemical nature of polyolefin surfaces after nitrogenation by an atmospheric-pressure afterglow, what kind of functional groups are formed? (2) What are the gas-phase species involved in formation of a specific functional group, can a plausible chemical pathway be demonstrated for its formation, in agreement with state-of-the-art knowledge about chemical mechanisms in general? (3) How does the rate of product formation depend on species densities, can a set of rate equations be formulated? From a more practical standpoint of plasma-based surface technology, the project will provide an exact description of discharge and postdischarge parameters to obtain a controlled surface modification of polyolefins with well-known nitrogen-containing functional Groups.