Spectroscopically Detecting Molecular-Level Bonding Formation between an Epoxy Formula and Steel

Abstract

The formation of the interfacial adhesion between an epoxy adhesive and a substrate was normally accompanied by the epoxy curing process on the substrate. Although the debate on the formation mechanism of the interfacial adhesion is still ongoing, this issue can causally be resolved by studying the interfacial structural formation between the epoxy adhesive and the substrate. Herein, to reveal the interfacial structural formation of a representative formula composed of epoxy (digylcidyl ether of biphenyl A, DGEBA) and amine hardener (2,2′-(ethylenedioxy) diethylamine, EDDA) with the steel substrate upon curing and postcuring treatments, sum-frequency generation (SFG) vibrational spectroscopy with a sandwiched transparent window/epoxy adhesive/steel setup was applied to detect and track the buried molecular-level structures at the epoxy adhesive/steel interface. An X-ray photoelectron spectroscopic (XPS) experiment was performed to probe the intentionally exposed interface to disclose the occurring interfacial chemical reaction. The reaction between the epoxy groups and the steel-surface OH groups and the molecular reconstruction of interfacial epoxy methyl groups upon curing and postcuring steps were confirmed. The latter also indirectly indicated the formation of the additional hydrogen bonding and the former bonding reaction at the interface. The above two spectroscopic experimental results matched up with the further examination of the adhesion strength. Therefore, this work elucidates the formation of the interfacial bonding between the epoxy formula and the steel substrate upon curing and postcuring treatments at the molecular level, thus providing an in-depth insight into the origin of the interfacial adhesion.

Enhanced Adsorption of Epoxy‐Functional Nanoparticles onto Stainless Steel Significantly Reduces Friction in Tribological Studies

“…(c) Two possible mechanisms for the enhanced adsorption of epoxy‐functional P(LMA 50 ‐ stat ‐GlyMA 9 )‐PBzMA 245 nanoparticles onto stainless steel: (i) hydrogen bond formation between the polar epoxy rings and the surface hydroxyl groups (i.e., Fe‐OH) or (ii) epoxy ring‐opening reaction with the same surface hydroxyl groups to produce covalent bonds. The experimental evidence reported herein supports the latter interaction, for which there is also some literature precedent [52, 53] …”

“…Moreover, the same team reported enhanced adhesion for an epoxy‐amine adhesive when cured in contact with a stainless steel substrate. Again, direct spectroscopic evidence was provided for a chemical reaction between the epoxy rings and the Fe‐OH groups [53] …”

“…Thus, such temperature‐dependent studies suggest that nanoparticle adsorption involves a chemical reaction between the epoxy groups and the Fe‐OH groups located at the stainless steel surface. Indeed, there is some recent literature precedent for such surface chemistry [52, 53] . Increasing the nanoparticle diameter from ca.…”

Enhanced Adsorption of Epoxy‐Functional Nanoparticles onto Stainless Steel Significantly Reduces Friction in Tribological Studies

“…The experimental evidence reported herein supports the latter interaction, for which there is also some literature precedent. [52,53] Angewandte Chemie…”

Label-Free Sensing of Biomolecular Adsorption and Desorption Dynamics by Interfacial Second Harmonic Generation

“…As a spatial region with a thickness usually smaller than 10 nm, label-free probing of the interfacial dynamics of biomolecules is challenging. Thus far, only limited label-free probing techniques have been developed, such as surface plasmon resonance [ 6 , 7 ], optical fiber sensors [ 8 ], time resolved sum-frequency generation [ 9 , 10 ], surface-enhanced Raman spectroscopy and so on [ 11 , 12 , 13 , 14 , 15 ]. These methods have significantly improved the performance of interfacial biosensing in terms of high sensitivity, high resolution and real-time observation, and have greatly deepened the understanding of the interfacial dynamics at the molecular level.…”