Self-Assembled Monolayers of Dodecyl and Hydroxy-dodecyl Phosphates on Both Smooth and Rough Titanium and Titanium Oxide Surfaces

Dodecyl phosphate and hydroxy-terminated dodecyl phosphate are shown to spontaneously assemble on smooth titanium oxide and titanium metal coated glass and silicon substrates, as well as on rough titanium metal implant surfaces. The surfaces were dipped in aqueous solutions of the corresponding ammonium salts for 48 h. The molecules are shown by X-ray photoelectron spectroscopy (XPS) to form densely packed, self-assembled monolayers (SAMs) on all surfaces investigated. The phosphate headgroups are believed to attach to the titanium (oxide) surface with the terminal end group (either methyl or hydroxy) pointing toward the ambient environment (air, vacuum, or water). Mixed SAMs are shown to be formed from mixed aqueous solutions of the two amphiphiles, with the hydroxy-terminated dodecyl phosphate adsorbing more favorably than the methyl-terminated molecule. The advancing water contact angles can be easily tailored via the composition of the self-assembly solution in the range of 110° (pure methyl) to 55° (...