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粘附增强、无电金属沉积或生物医学目的的应用中获得了很大的兴趣，仅举重要的例子。等离子体氮化的聚合物表面与等离子体氧化的聚合物表面的不同之处在于它们的碱性和亲核性，由具有未键合电子对的N-官能团引入，而含氧聚合物表面通常是酸性和亲电子的。尽管等离子体氮化聚合物表面的重要性，但目前关于用氮气或含氮气体等离子体处理聚合物表面的理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，应主要研究N2中的大气压DBD与聚烯烃表面和模型化合物的相互作用。首先，应利用N2中介质阻挡放电提供的流动后放电进行这些研究，作为活性物质的来源，这些活性物质应在表面改性中发挥主导作用。该项目旨在确定上述相互作用的产品，即。例如，引入到聚合物表面的官能团，以及产物形成的机理和动力学，基于主要涉及的反应物种的气相密度：基态和亚稳态激发原子，N（4S）和N（2 P），以及亚稳态激发分子，N2（A）。密度可以由光发射光谱和化学动力学计算以足够的精度确定。为了分析表面，将应用衰减反射模式下的傅里叶变换红外光谱法或浸没-IRRAS（红外反射-吸收光谱法）以及X射线光电子光谱法。还将使用化学衍生和捕获技术对产物进行分类和定量，并稳定不稳定部分。模型烷烃的实验还将通过气相色谱法结合高分辨率质谱法进行评价。该项目的科学目标是回答三个基本问题：（1）大气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)什么是气相物质参与形成一个特定的功能团，可以证明一个合理的化学途径，其形成，与国家的最先进的知识，一般的化学机制？(3)产物生成速率如何依赖于物种密度，能否用公式表示一组速率方程？从基于等离子体的表面技术的更实用的角度来看，该项目将提供放电和放电后参数的准确描述，以获得具有众所周知的含氮官能团的聚烯烃的受控表面改性。

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.