Hexadecylamine adsorption at the iron oxide-oil interface

Area of Science:

• Surface Science
• Materials Chemistry
• Physical Chemistry

Background:

• Understanding additive adsorption on metal surfaces is crucial for corrosion inhibition and lubrication.
• Hexadecylamine is a common model additive used to study surface interactions.
• Iron and its alloys are widely used in industrial applications, making their surface chemistry important.

Purpose of the Study:

• To characterize the adsorption behavior of hexadecylamine on an iron surface from hexadecane oil.
• To determine the structure, orientation, and dominant interaction mechanism of the adsorbed amine layer.
• To correlate adsorption properties with surface analytical data.

Main Methods:

• Polarized neutron reflectometry (PNR) for layer thickness and density.
• Sum-frequency generation (SFG) spectroscopy for molecular orientation and conformation.
• Solution depletion isotherm for adsorption quantification.
• X-ray photoelectron spectroscopy (XPS) for surface chemical states and bonding.

Main Results:

• Hexadecylamine forms a dense monolayer on iron with strong surface affinity.
• PNR data indicated a layer thickness of 16-20 Å, suggesting tilted molecules.
• XPS revealed dominant interaction via nitrogen lone pair electron donation to iron ions.
• SFG spectroscopy provided insights into alkyl chain order and orientation.

Conclusions:

• Hexadecylamine adsorbs strongly to iron surfaces, forming tilted monolayers.
• The primary adsorption mechanism involves electron donation from nitrogen to iron.
• Multiple spectroscopic and surface techniques provide complementary information on adsorption behavior.