Cathodic delamination kinetics of thin polystyrene model coatings bound to zinc via organosilanes

Abstract

The cathodic delamination of poly(styrene) [PS] model coatings from oxide‐covered zinc has been evaluated by scanning Kelvin probe (SKP). Linear and acrylate cross‐linked PS model coatings covalently bound to zinc oxide via ZnOSi bonds have been prepared. PS was prepared by thermally initiated free radical polymerization in the presence of vinyltrimethoxy silane modified zinc. Cross‐linkers ethylene glycol diacrylate (EDA) and hexanediol diacrylate (HDA) were used in some preparations. Resulting polymers are 8–15 nm thick. PS model coatings show a delamination rate of only ≈20% of that of comparable poly(methyl methacrylate) [PMMA] samples. The slower cathodic delamination of PS is attributed to denser chain packing and higher amounts of hydrophobic moieties, leading to a reduction in penetration of corrosive species. As opposed to the situation in PMMA, the addition of HDA increases the delamination rate, due to its flexible chains and hydrophilic groups. The lowest delamination rate is observed in the presence of 25% EDA. Consequently, ester hydrolysis of acrylates accelerates delamination, it is however not the main factor in cathodic delamination of such thin model system.

Molybdate and Phosphate Cross-Linked Chitosan Films for Corrosion Protection of Hot-Dip Galvanized Steel

“…The delamination rate of the chitosan-phosphate system is (0.19 ± 0.01) mm h –1 slightly higher, and the rate of the chitosan-molybdate system is (0.28 ± 0.01) mm h –1 , circa twice as high as the lowest rate observed. Generally, delamination rate decreases as cross-linking density increases. ,, Despite the fact that diffusive processes are not rate-determining, it is very probable that slow processes are involved such as diffusion of the ions formed in the first hours of the delamination and oxygen transport. At this point, deposition of phosphate and molybdate at the metal–polymer interface cannot be discarded.…”

“…A main aim of this work is to broaden the data basis for understanding the chemical processes during cathodic delamination by comparing systems with well-defined interfacial linkage, − thus broadening the understanding of the chemical processes during cathodic delamination in the presence of weak model top coatings . Deadhesion kinetics with a weak model top coating was characterized by scanning Kelvin probe (SKP) experiments, in line with community standards .…”

Delamination Kinetics of Thin Film Poly(acrylate) Model Coatings Prepared by Surface Initiated Atom Transfer Radical Polymerization on Iron

“…4 In the more hydrophobic poly(styrene) system on zinc, the effect of crosslinking was more involved. 58 While the initiator alone has not been investigated here, based on the experience from the Zn-PMMA system, a significant effect is to be expected here as well. In particular, an investigation of several acrylates on iron showed that PMMA alone is an extremely weak coating, weaker even than PVB.…”

Dynamic Electrochemical Impedance Spectroscopy for the Evaluation of Localised Corrosion on Aluminium Alloys

“…Because of the difficulty of determining the correct area ratio between anodic and cathodic region and the Ohmic drop due to the electrolyte resistance any correlation between the electrochemical properties and corrosion properties shall be expected to be of qualitative nature. In other mechanisms of underpaint corrosion, correlation between corrosion current density and disbonding rate is also not always given [42] …”

“…In other mechanisms of underpaint corrosion, correlation between corrosion current density and disbonding rate is also not always given. [42] For this study, we use anodised 3005 aluminium alloys with Cu content in the range 0.15-0.22 wt. % and Mn content in the range 1.08-1.39 wt-%, i. e., with only relatively minor variations in composition.…”