Effect of the Organic Functional Group on the Grafting Ability of Trialkoxysilanes onto Graphene Oxide: A Combined NMR, XRD, and ESR Study

Abstract

The functional properties displayed by graphene oxide (GO)-polymer nanocomposites are strongly affected by the dispersion ability of GO sheets in the polymeric matrix, which can be largely improved by functionalization with organosilanes. The grafting to GO of organosilanes with the general formula RSi(OCH3)3 is generally explained by the condensation reactions of silanols with GO reactive groups. In this study, the influence of the organic group on the RSi(OCH3)3 grafting ability was analyzed in depth, taking into account the interactions of the R end chain group with GO oxidized groups. Model systems composed of commercial graphene oxide reacted with 3-aminopropyltrimethoxysilane (APTMS), 3-mercaptopropyltrimethoxysilane (MPTMS), and 3-methacryloxypropyltrimethoxysilane, (MaPTMS), respectively, were characterized by natural abundance 13C, 15N and 29Si solid state nuclear magnetic resonance (NMR), x-ray diffraction (XRD), and electron spin resonance (ESR). The silane organic tail significantly impacts the grafting, both in terms of the degree of functionalization and direct interaction with GO reactive sites. Both the NMR and XRD proved that this is particularly relevant for APTMS and to a lower extent for MPTMS. Moreover, the epoxy functional groups on the GO sheets appeared to be the preferential anchoring sites for the silane condensation reaction. The characterization approach was applied to the GO samples prepared by the nitric acid etching of graphene and functionalized with the same organosilanes, which were used as a filler in acrylic coatings obtained by cataphoresis, making it possible to correlate the structural properties and the corrosion protection ability of the layers.

Effects of Graphene-Based Fillers on Cathodic Delamination and Abrasion Resistance of Cataphoretic Organic Coatings

“…These images are very interesting as it is very rare to be able to observe a graphene-based flake in profile, and even more difficult to analyse the presence of particular elements on its plane. These qualitative results confirm the effective presence of silane on the surface of the GO flakes, as previously studied in depth with infrared spectroscopy, X-ray diffraction analysis, and nuclear magnetic resonance techniques [44,45].…”

“…In previous studies, different types of silanes have been analysed [44], with particular attention to their grafting mechanism and interaction with GO flakes. Higher affinity and reactivity of (3-aminopropyl) trimethoxysilane (APTMS) were found compared with other organosilanes.…”

Graphene-Based Reinforcing Filler for Double-Layer Acrylic Coatings

“…The cataphoretic layers were reinforced by means of functionalized graphene oxide (fGO) powder, synthetized according to the procedures performed in previous works [ 47 , 58 , 59 , 60 ].…”

“…The graphene-based fillers were not characterized in this work, as the same products were already widely investigated by means of optical stereomicroscope, scanning transmission electron microscope observations [ 60 ], infrared (FTIR) and X-ray diffraction (XRD) analysis [ 47 , 59 ] and nuclear magnetic resonance (NMR) measurements [ 58 ].…”

“…A recent study [ 58 ] demonstrated the high reactivity of (3-aminopropyl)trimethoxysilane (APTMS) in interacting with graphene oxide flakes. Nuclear magnetic resonance (NMR) analyses highlighted the effectiveness of the silane functionalization process, even when the sheets’ oxidation level is limited.…”