Alkylphosphonate modified aluminum oxide surfaces.

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Surface properties of aluminum are critical for micro-/nano-electromechanical systems (MEMS/NEMS).
• Chemical modification of aluminum surfaces can alter key properties like friction, adhesion, and hydrophobicity.

Purpose of the Study:

• To investigate the surface properties of aluminum substrates chemically reacted with octadecylphosphonic acid (ODP/Al), decylphosphonic acid (DP/Al), and octylphosphonic acid (OP/Al).
• To characterize the impact of these modifications on surface chemistry, roughness, hydrophobicity, surface energy, friction, and adhesion.

Main Methods:

• X-ray photoelectron spectroscopy (XPS) for chemical composition analysis.
• Contact angle measurements to determine hydrophobicity.
• Atomic force microscopy (AFM) for surface roughness and friction force microscopy (FFM) for tribological properties.
• Zisman plot method for surface energy determination.

Main Results:

• XPS confirmed the successful grafting of alkylphosphonate molecules onto aluminum surfaces.
• All modified aluminum surfaces (ODP/Al, DP/Al, OP/Al) exhibited high hydrophobicity, with contact angles >105 degrees.
• Surface roughness remained below 15 nm for all samples.
• ODP/Al showed the lowest coefficient of friction, while bare aluminum had the highest.
• Surface energies were measured as ~21 mJ/m² for ODP/Al, ~22 mJ/m² for DP/Al, and ~25 mJ/m² for OP/Al.

Conclusions:

• Chemical modification of aluminum with alkylphosphonic acids effectively creates hydrophobic surfaces with tunable properties.
• These modifications significantly reduce friction and maintain comparable adhesion, indicating potential for improved performance in MEMS/NEMS applications.
• The study highlights the importance of surface functionalization for tailoring material properties at the micro- and nanoscale.