Adsorption of organic molecules at sufaces: A first principles investigation

Abstract

The adsorption of a molecule at a surface is a fundamental step in a wide variety of industrially relevant phenomena, including adhesion, corrosion, and catalysis. The work presented in this thesis is motivated by the desire to contribute to a better understanding of the factors affecting the adhesion between an organic coating/adhesive and an aluminium alloy surface. A key factor is the nature and strength of the interfacial bonds between the binder polymers of the organic coating/adhesive and the substrate. The size of the polymers and complexity of the polymer-substrate interactions preclude a detailed, atomic-level description. The strategy followed in this thesis is to study the adsorption of small organic molecules, representing fragments of the industrially relevant amine-cured epoxides, with various surfaces, of metal oxides (α-Al2O3(0001) and α-Cr2O3(0001)), bimetallic alloys (NiAl(110)), and graphite(0001). This thesis consists of two parts, an introductory text and a collection of five papers. In the included papers we present results from density functional theory (DFT) calculations on the adsorption of methanol and methylamine on α-Al2O3(0001) and α-Cr2O3(0001), phenol on α-Al2O3(0001) and graphite(0001), and methoxy on α-Cr2O3(0001) and NiAl(110). We describe in detail the adsorption sites and geometry, and the nature and strength of the bonding at these surfaces. The majority of adsorption systems considered in this thesis are well described by traditional implementations of DFT. However, the adsorption of phenol on graphite is predominantly governed by van der Waals interactions. These interactions requires approximations beyond traditional DFT. In this thesis a recently presented functional (vdW-DF) is employed, and is found to be of decisive importance for describing the phenol-graphite interactions. We calculate the contribution from vdW interactions to the adsorption of phenol on α-Al2O3(0001), and compare their contribution to the adsorption bond to other forces