Comparative Molecular Adhesion Studies of Polyacrylic Acids on ZnO Single Crystal Surfaces and ZnO Nanocrystalline Films

该提案涉及大分子在氧化锌单晶表面和技术上相关的纳米氧化锌层上的相对附着力的主题。本项目的基本目的是用单分子力谱分析水溶液中聚丙烯酸和氧化锌表面之间的界面作用力和化学。除了范德华作用力外，这种界面作用力还包括静电相互作用、氢键和配位键。它们的强度受晶面取向、晶面末端、吸附层的性质以及丙烯酸和晶面的双电层的影响。对这些界面相互作用的分析应有助于了解含有羧酸的聚合物与氧化锌或氧化锌涂层基材之间的微观和宏观粘合过程。这些粘接过程对氧化锌基复合材料和聚合物涂层锌合金在环境和腐蚀条件下的功能和稳定性具有重要意义。为了对这种界面过程有一个基本的了解，我们将研究极性和非极性的氧化锌单晶：它们允许详细分析表面终止，同时在与电解液中界面稳定性相关的环境条件下是稳定的。用非原位电子衍射(LEED)和X射线光电子能谱(XPS)表征了氧化锌衬底的表面化学结构，用扫描原子力显微镜(AFM)原位分析了表面形貌和表面电荷。使用聚乙二醇键的单分子力谱研究聚丙烯酸在电解质/氧化物界面上的相互作用，作为表面化学和电解质组成的函数。此外，还将研究特定吸附的阴离子对不同晶向的大分子吸附/脱附行为的影响，以了解含丙烯酸的聚合物在腐蚀环境中对氧化锌的粘附性。对纳米晶氧化锌纳米线层进行的类似研究还应该允许比较大分子的纯化学吸附和在氧化锌棒之间的受限间隙中大分子的固定。通过这些研究，我们对聚合物/氧化物在水溶液中的界面结合过程有了基本的了解和预测。

The proposal addresses the topic of the comparative adhesion of macromolecules onto zinc oxide monocrystalline surfaces and onto technologically relevant nanocrystalline zinc oxide layers. The fundamental aim of this project is the analysis of the interfacial forces and chemistry between polyacrylic acids and zinc oxide surfaces in aqueous electrolytes by means of single molecule force spectroscopy. Beside van-der-Waals forces, such interfacial forces comprise electrostatic interactions, hydrogen bonds and coordinative bonds. Their strength is influenced by the orientation of the crystal surface, its termination, the nature of the adsorbate layer and the electric double layers of the acrylic acid and the crystal surface. The analysis of these interfacial interactions should allow for the understanding of microscopic and macroscopic adhesion processes between polymers with carboxylic acids and zinc oxide or zinc oxide-coated substrates. These adhesion processes are of great importance for the functionality and stability of ZnO-based composite materials and polymer-coated zinc alloys under ambient and corrosive conditions. To gain a fundamental understanding of such interface processes, polar and nonpolar ZnO single crystals will be studied: they allow for a detailed analysis of the surface termination and at the same time are stable under the ambient conditions relevant for interface stability in electrolytes. The surface chemistry of ZnO substrates will be characterised by ex-situ electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS); surface topography and surface charge will be analysed in-situ by means of scanning Atomic Force Microscopy (AFM). The interaction of the polyacrylic acid at the electrolyte/oxide interface will be investigated by means of single molecule force spectroscopy using PEG-linkers as a function of the surface chemistry and the electrolyte composition. Moreover, the influence of specific adsorbed anions on the adsorption/desorption behaviour of the macromolecules as a function of different crystallographic orientations will be studied in order to understand the adhesion of acrylic acid-containing polymers to zinc oxide in corrosive environments. Similar studies performed on nanocrystalline ZnO-nanowire layers should additionally allow for a comparison of the pure chemisorption of the macromolecule with the immobilisation of the macromolecule in the confined gaps between the ZnO rod. From these studies we aim at gaining fundamental understanding and prediction of interfacial binding processes at polymer/oxide interfaces in aqueous electrolytes.