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Updated: Sep 26, 2025
09:43
Interfacial Molecular-level Structures of Polymers and Biomacromolecules Revealed via Sum Frequency Generation Vibrational Spectroscopy
Published on: August 13, 2019
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Molecular-Level Correlation between Spectral Evidence and Interfacial Bonding Formation for Epoxy Adhesives on Solid
Zhaohui Xu1, Yinyu Zhang2, Yeping Wu2
1State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China.
Langmuir : the ACS Journal of Surfaces and Colloids
|April 20, 2022
Summary
This study used sum frequency generation (SFG) spectroscopy to reveal molecular-level changes in epoxy-based adhesives during curing on sapphire and silica surfaces. Stronger interactions and chemical bonding were observed on sapphire, correlating with higher adhesion strength.
Area of Science:
- Materials Science
- Surface Chemistry
- Spectroscopy
Background:
- Epoxy-based adhesive bonding strength is crucial for material applications.
- Understanding interfacial interactions during curing at a molecular level remains challenging.
- The curing process at the interface differs significantly from the bulk material.
Purpose of the Study:
- To investigate the interfacial structural evolution of an epoxy adhesive (DGEBA/EDDA) on sapphire and silica substrates.
- To probe molecular-level interfacial bonding formation during curing and post-curing using SFG vibrational spectroscopy.
- To correlate spectroscopic findings with macroscopic adhesion strength.
Main Methods:
- Sum Frequency Generation (SFG) vibrational spectroscopy was employed to analyze interfacial structures.
- The study focused on diglycidyl ether of biphenyl A (DGEBA) and 1,2-bis(2-aminoethoxy)ethane (EDDA) epoxy system.
- Experiments were conducted on sapphire and fused silica substrates during curing and post-curing stages.
Main Results:
- On sapphire, decreased methylene (CH2) signals and increased surface hydroxyl (OH) signals indicated rigidification and strong polar/hydrogen bonding.
- Post-curing on sapphire showed increased CH2 and decreased OH signals, suggesting chemical bond formation between epoxy and substrate.
- Silica exhibited weaker CH2/CH3 signals and very weak OH signals, indicating a less hydrophilic surface and weaker interfacial interactions compared to sapphire.
Conclusions:
- SFG spectroscopy successfully traced the molecular-level interfacial structural evolution of epoxy adhesives.
- Sapphire surfaces promote stronger interfacial interactions and chemical bonding, leading to enhanced adhesion.
- The study establishes a correlation between molecular-level interfacial structure and macroscopic bonding strength.
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