Interfacial Water at Polyurethane-Sapphire Interface

Area of Science:

• Materials Science
• Surface Chemistry
• Spectroscopy

Background:

• Understanding interfacial behavior is crucial for material performance.
• Polyurethane (PU) and sapphire interfaces are relevant in coatings and adhesion applications.
• The role of water at buried interfaces requires direct probing methods.

Purpose of the Study:

• To investigate the interfacial structure of water between polyurethane and sapphire.
• To differentiate the effects of liquid water versus water vapor on the interface.
• To understand how water influences interfacial interactions and adhesion.

Main Methods:

• Utilized infrared-visible sum frequency generation (SFG) spectroscopy.
• Probed the interface of polyurethane and sapphire samples exposed to liquid water and water vapor.
• Analyzed SFG peaks corresponding to water and substrate functional groups.

Main Results:

• Liquid water formed a hydrogen-bonded network at the PU/sapphire interface, disrupting interactions.
• Water vapor reached the interface but formed low-coordination water or hydroxyl groups, not a uniform layer.
• Water vapor exposure altered PU hydrocarbon and sapphire hydroxyl group signals without complete disruption of interactions.

Conclusions:

• The state of water (liquid vs. vapor) significantly impacts interfacial structure and interactions.
• Water's effect on PU/sapphire adhesion depends on its molecular arrangement at the interface.
• Findings have implications for designing durable coatings and preventing corrosion.