Eva Pospisilova oral presentation (OB2-Mon2-2-2)
Cross-linking degree of benzoxazine thin coatings determined by ToF-SIMS
1 Universite Catholique de Louvain, Place Louis Pasteur 1, 1348 Louvain-la-Neuve, Belgium
2 imec - KU Leuven, Kapeldreef 75, 3001 Leuven, Belgium
3 Instituut voor Kern- en Stralingsfysica - KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
4 Materials Engineering Research Center (CRIM), Univeristy of Mons, Rue de l'Epargne 56, 7000 Mons, Belgium
In 2017, the use of bio-toxic chromates has been banned. This change in law has affected aeronautical industry, where chromates were used for anti-corrosion treatments of aluminum alloys. New materials are studied to replace the chromates and poly-benzoxazines exhibit promising properties . In this study we focus on para-phenylenediamine benzoxazines (P-pPDA), which have been already studied by electro-chemical impedance spectroscopy (EIS) and exhibit excellent barrier properties. However, it seems that fully cross-linked P-pPDA coatings delaminate from the aluminum alloy during saline tests . The decrease of the curing temperature to avoid the delamination of the coating while preserving the mechanical properties of the alloy as well as the barrier properties of the coating is necessary. A decrease of curing temperature leads to partially cross-linked P-pPDA coatings. In the case of partially cross-linked epoxy resins, cross-linking degree is evaluated in bulk samples by differential scanning calorimetry (DSC), however in the case of thin films a tool for evaluating the cross-linking is missing. Therefore, a study dealing with partially cross-linked P-pPDA coatings has been conducted using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Partially cross-linked coatings were obtained by spin-coating a laboratory synthesized P-pPDA solution on silicon wafers and applying curing cycles in the temperature range from 100°C to 200°C. The SIMS data were calibrated with DSC for a first set of samples. As a result, a novel method using the ratio of intensities for different groups of sputtered fragments of the P-pPDA monomer and fragments of the polymerized material was developed. This protocol allows measuring the cross-linking degree of the P-pPDA coatings not only locally, at the surface, but also along the depth of the coating using dual-beam depth profiling with large Ar cluster sputtering. Other protocols, involving the total spectrum intensities, the sputtering yield of the polymer and the backscattering of Ar clusters are also investigated and compared. Via these new approaches, ToF-SIMS provides access to very detailed information about the cross-linking degree of thin organic coatings.
 H. Ishida, D. Allen, J. Polym. Sci. B: Polym. Phys. (34), 1996, 1019–1030.
M. Poorteman, A. Renaud, J. Escobar, L. Dumas, L. Bonnaud, P. Dubois, M.-G. Olivier, Prog. Org. Coat., (97), 2016, 99 – 109.