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

• Applicant: Professor Dr.-Ing. Guido Grundmeier
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Solid State and Surface Chemistry, Material Synthesis ; Synthesis and Properties of Functional Materials
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 320414069

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.

• DFG Programme: Research Grants