Molecular Characterization of Bonding Interactions at the Buried Steel Oxide–Aminopropyl Triethoxysilane Interface Accessed by Ar Cluster Sputtering

Abstract

The overall performance of any organic coating system on a metal is largely dependent on the primer coating which has the crucial function to ensure adhesion to the metal substrate. Although performance in terms of adhesion can be empirically measured, the underlying chemical adhesion mechanism is dicult to unravel. A detailed molecular characterization of interfacial chemistry is required for this purpose, but brings up the challenge to reach the buried interface without inducing excessive damage to its molecular structure. In this work, argon gas cluster ions are being applied to sputter through an aminosilane coating on steel, in order to access the steel oxide 1 silane interface with time-of-ight secondary ion mass spectrometry (ToF-SIMS). In-situ atomic force microscopy (AFM) measurements during the sputter process demonstrate the importance of optimizing the Ar gas cluster ion beam in order to minimize sputter induced roughness and molecular damage. ToF-SIMS spectra obtained at the buried steel oxide aminosilane interface accessed by sputtering were compared to spectra from a steel oxide aminosilane interface that was directly accessible without the need for sputtering. This comparison allowed to identify contributions from sputter induced damage in the buried interface spectra. Fragments characteristic for interfacial bonding interactions could be extracted, although there is a signicant loss of molecular information due to sputtering. Nevertheless, insights on the role of steel surface hydroxyl groups in the adsorption mechanism of aminosilanes could be obtained through deuteration of the steel substrate.

Nanostructured Poly(methyl Methacrylate)–Silica Coatings for Corrosion Protection of Reinforcing Steel

“…20 The covalent bonding between the silanol groups and the iron hydroxyls of the reinforcing steel surface is responsible for this excellent adhesion of the hybrid. 18,19 The highest adhesion value of 15.9 MPa was achieved for the B0.05 sample with an intermediate BPO/MMA ratio. This suggests the existence of a sensitive balance between the decreasing fraction of the silica phase (Table S2), which impairs adhesion strength, and the reduction of the average spacing between the silica nanodomains (Table 1), which favors better adhesion.…”

“…The pull-off assays showed a high critical tensile adhesion strength to the steel surface for the hybrid coatings with values of 11.1, 15.9, and 14.7 MPa for B0.025, B0.05, and B0.1 samples, respectively (Table ), which are significantly higher than the value of 6.7 MPa reported for pure PMMA coatings on carbon steel 1020 and on the Ti6Al4V alloy . The covalent bonding between the silanol groups and the iron hydroxyls of the reinforcing steel surface is responsible for this excellent adhesion of the hybrid. , The highest adhesion value of 15.9 MPa was achieved for the B0.05 sample with an intermediate BPO/MMA ratio. This suggests the existence of a sensitive balance between the decreasing fraction of the silica phase (Table S2), which impairs adhesion strength, and the reduction of the average spacing between the silica nanodomains (Table ), which favors better adhesion.…”

“…Recent results showed that the anticorrosive performance and durability of PMMA–silica coatings depend sensitively on the type of interphase between the uniformly distributed silica nodes and the polymeric phase, as well as the proportion between both phases and the amount of thermal initiator of polymerization. , The covalent conjugation of PMMA with silica nanodomains through a molecular coupling agent such as MPTS is the key element in achieving a dense nanostructured hybrid network that acts as an efficient barrier against the diffusion of corrosive species. The silica phase is responsible for the contraction of the polymeric segments − , and the adhesion of the coating to the metallic surface, , while the PMMA matrix contributes to maintain a hermetically sealed nanostructure. ,,, This type of hybrid material was investigated as a protective coating on carbon steel, − aluminum alloys, ,, and titanium alloy; however, studies on reinforcing steel were not reported so far. In addition, in previous studies, tetrahydrofuran (THF) was used as a solvent, presenting disadvantages associated with environmental and health impacts, flammability, reactivity, and stability …”

“…10,13 The covalent conjugation of PMMA with silica nanodomains through a molecular coupling agent such as MPTS is the key element in achieving a dense nanostructured hybrid network that acts as an efficient barrier against the diffusion of corrosive species. The silica phase is responsible for the contraction of the polymeric segments [10][11][12][13]17 and the adhesion of the coating to the metallic surface, 18,19 while the PMMA matrix contributes to maintain a hermetically sealed nanostructure. 10,11,13,20 This type of hybrid material was investigated as a protective coating on carbon steel, 10−12 aluminum alloys, 13,21,22 and titanium alloy; 20 however, studies on reinforcing steel were not reported so far.…”