Surface treatment of polyolefines by ambient-pressure discharges in N2-H2 mixtures - steps towards a new perspective

在之前的DFG项目（利用大气压屏障放电对聚合物的等离子基胺化的ATR-FTIR原位研究）（Kl1096/19-1； 24个月）中，我们证明了芳香醛的衍生化，迄今为止通常用于等离子处理的聚合物表面上的伯胺基- nh2的量化，并不仅限于胺，但也适用于其他官能团，如亚胺>C=N-。因此，与其他含氮官能团相比，氨基的作用在过去可能被高估了。应用FTIR-ATR原位研究氮等离子体处理聚乙烯表面和随后的H/D同位素交换或4三氟甲基苯甲醛的化学衍生化，我们表明，虽然不能用独立的方法（N-H与N-D的交换和预期ND2变形振动区域的红外光谱）检测到伯胺，但与醛的衍生化反应可能发生。这些发现对此类表面的应用以及对其化学性质和形成机制的理解具有重要意义。拟建项目的目的是通过对氮等离子体处理表面的组成和反应性进行物理化学研究，来弄清这些后果。为了验证表面化学是由兼具亲核和亲电性质的亚胺基主导而不是由胺主导的假设，我们将使用FTIR-ATR光谱原位研究与亲电和亲核试剂的化学气相衍生反应。所得的光谱将与在合适的模型化合物上测得的光谱进行比较。此外，将对等离子体处理的聚合物箔进行非原位测量，并将包括湿化学反应（还原，水解），以从新的角度获得这些表面的全面图像。化学研究将分别与柏林和克劳斯塔尔的研究伙伴联合使用NEXAFS、UPS和MIES进行物理测量；这些方法提供了额外的可能性来获得有关表面化学成分不饱和程度的信息（CH=CH- vs. - ch2 - ch2 -和-CH=N- vs. - ch2 - nh -）。关于等离子体氮化机制的一个问题是氮原子和氢在通常使用的N2-H2混合物中的作用。为此，计划在H2含量在0 - 4%之间变化的等离子体处理期间进行原位FTIR-ATR研究。这些研究应辅以光学发射测量，目的是对放电余辉中的N原子进行定量研究。基于这些数据，应该可以评估N原子和由此形成的激发的N2分子是否可能对表面修饰负责，或者是否必须考虑到另一种含氢物质NHx。

In the preceding DFG project (ATR-FTIR studies in situ of plasma-based amination of polymers using atmospheric-pressure barrier discharges) (Kl1096/19-1; 24 months) we demonstrated that the derivatization with aromatic aldehydes, hitherto commonly applied for quantification of primary amino groups -NH2 on plasma treated polymer surfaces, is by no means specific to amines but will also work with other functional groups such as imines >C=N-. Therefore the role of amino groups has probably been overestimated in the past, compared with alternative nitrogen-bearing functional groups. Applying FTIR-ATR in situ to the study of nitrogen-plasma treatment of polyethylene surfaces and the subsequent H/D isotope exchange or chemical derivatization with 4 trifluoromethyl-benzaldehyde we showed that a derivatization reaction with the aldehyde may take place although primary amines could not be detected with an independent method (exchange of N-H vs. N-D and IR spectroscopy of the region of expected ND2 deformation vibrations). These findings bear consequences for the applications of such surfaces as well as for the understanding of their chemical properties and formation mechanism.The purpose of the proposed project is to fathom these consequences, using physico-chemical investigations of the composition and reactivity of the nitrogen-plasma-treated surfaces. In order to test the hypothesis that the surface chemistry is dominated by imino groups, featuring both nucleophilic and electrophilic properties, rather than by amines, chemical gas-phase derivatization reaction with electrophilic and nucleophilic reagents will be studied in-situ using FTIR-ATR spectroscopy. Obtained spectra will be compared with those measured on suitable model compounds. In addition ex-situ measurements will be performed on plasma-treated polymer foils and wet-chemical reactions (reductions, hydrolyses) shall be included to obtain a comprehensive picture of these surfaces from a new perspective. The chemical studies will be complemented by physical measurements using NEXAFS, UPS and MIES jointly with research partners in Berlin and Clausthal, respectively; these methods offer additional possibilities to gain information with respect to the degree of unsaturation of chemical moieties on the surface ( CH=CH- vs. -CH2-CH2- and -CH=N- vs. -CH2-NH-).A question concerning the mechanism of plasma nitrogenation is the role of nitrogen atoms and hydrogen in the N2-H2 mixtures normally used. To this end FTIR-ATR studies in situ are planned during plasma treatment with varying H2 content between 0 and 4 %. These investigations shall be complemented by optical emission measurements aiming at a quantitative study of N atoms in the discharge afterglow. Based on these data it should be possible to assess if N atoms and excited N2 molecules formed therefrom may be responsible for the surface modification or if alternatively hydrogen-bearing species NHx have to be taken into consideration.