Obtaining a poly-epoxy surface model and its reactivity – OPOSUM

Polymers and composites are found in all modern industrial applications, from nanomedicine to communication satellites. The knowledge of their surface is a strategic challenge. Despite a few pioneering studies, it was only recently that research has started targeting the simulation of polymer surfaces. And these are very limited beginnings, with only few experimental data that can be used as inputs for theoretical studies. Nevertheless, the surface is the value-added of a great majority of advanced materials, and noticeably when the surface is functionalized. Then, beyond the unique increase of knowledge, the definition of models for the surface of polymers will allow the optimization of surface treatments that are still too much empirical. To that aim, it is necessary to define specific features of polymer surfaces (e.g. microstructure, composition, relaxation, etc.), as long as their reactivity and dynamical phenomena which take place on them. OPOSUM pursues these objectives, focusing on the surface of poly-epoxies, which are of great interest for paintings, adhesives, and composite materials. Noticeably, poly-epoxies are widely used in the aerospace industry. The PI has been studying the coating of the surface of composite components used in communication satellites for the last seven years, until he could establish a joint laboratory with an SME partner. But the lack of generic knowledge about these surfaces has always been a hindrance to the efficient solving of the metal/composite adherence bottleneck. Trial and error methods are costly and do not produce too much re-usable knowledge. This observation drives the OPOSUM project, which includes an ambitious methodology based on the combination of experiments and calculations. The experimental part consists in the synthesis of “model” polymer surfaces; “Model” meaning that the surface shows very few defects, that its chemical composition is homogeneous, and that its roughness is less than one nanometer. Consecutively, we render possible the study of widely-used industrial materials by fine techniques, such as atomic force microscopy (AFM) or x-ray photoelectron spectroscopy (XPS). In parallel, quantum mechanics calculations (density functional theory, DFT) and classical molecular dynamics calculations (MD) are developed in order to simulate mixture of monomers, the polymerization process in the presence of vacuum, and the resulting free surfaces. Finally, simulated and experimental surfaces are studied and compared, before they are used as templates for studying the mechanisms of formation of metallic thin films. Preliminary results led by the PI demonstrate the efficiency of the method, allowing a drastic improvement of the analysis of XPS spectra of a poly-epoxy surface. This example illustrate potentialities of the project; the surface of this polymer is better known, and the accuracy of the XPS analysis has been set to an unequalled level. Now, it is time to propose a more ambitious work program including an improved methodology, and an increased materials complexity. In OPOSUM, the PI will lead an innovative strategy with human and material resources that will create generic knowledge dedicated to the scientific community, and to students in Materials Sciences classes.