Understanding the interface structures of water-based and solvent-based poly(methyl methacrylate) coatings at the molecular level

Water-based polymer coatings usually exhibit poor adhesion performance compared to their solvent-based counterparts. Unveiling the difference in interface structures between water-based and solvent-based polymer coatings will help to improve the adhesion performance of water-based polymer coatings. Herein, sum frequency generation (SFG) vibrational spectroscopy was utilized to detect the buried interfaces of water-based and solventbased polymer coatings. Water-based poly(methyl methacrylate) (PMMA) coatings containing sodium dodecyl sulfate (SDS) as an emulsifier and solvent-based PMMA coatings using toluene as solvent were selected as the model systems for this investigation. The results demonstrate that the interface between water-based PMMA and silica substrate is mainly occupied by SDS and water molecules, and the polymer chains show random-coil conformations due to their encapsulation by SDS. In contrast, for the solvent-based PMMA, the PMMA chains directly contact the silica substrate and exhibit stretched chain conformations at the interface. The interface structure of water-based PMMA coatings can be improved by annealing at Tg + 70 celcius to form an adsorbed polymer layer. This work reveals the origin of the difference in the adhesion strength of water-based and solventbased polymer coatings at the molecular level, which is significant for the design and performance optimization of water-based polymer coatings.

Automated summary

Analysis using SFG vibrational spectroscopy detected distinct interface structures between water-based and solvent-based polymer coatings. Water-based PMMA coatings showed SDS and water molecules at the interface, while solvent-based PMMA coatings exhibited direct contact between PMMA chains and the substrate. Heat treatment was found to enhance the interface structure of water-based PMMA coatings, revealing the molecular level origin of the adhesion strength difference between water-based and solvent-based polymer coatings.