Anchoring of sulfur-containing alkylphosphonic and semifluorinated alkylphosphonic molecules on a polycrystalline aluminum substrate

Structure and conformation of methyl-terminated poly(ethylene oxide)-bis[methylenephosphonate] ligands adsorbed to boehmite (AlOOH) from aqueous solutions. Attenuated total reflection infrared (ATR-IR) spectra and dynamic contact angles

A ligand with a bisphosphonate headgroup and methyl-terminated poly(ethylene oxide) 550 tail has been adsorbed to a boehmite (AlOOH) particle film from aqueous solutions at 9, 18, 26, and 40 degrees C with a range of coverages. In situ attenuated total reflectance infrared (ATR-IR) spectra of the PEO-modified boehmite particle films has been used to monitor surface coverage. PEO-related IR absorptions showed variation in band shape with coverage and temperature which reflect changes in the configuration and crowding of PEO ligand tails. The integrated absorbance of PEO-related absorptions arising from CH(2) wagging and twisting vibrations indicated the average conformation about the C-C and C-O bonds. At all values of coverage and temperature, the PEO tails of the PEO-phosphonate ligands were found to have a predominantly gauche conformation about C-C bonds and a predominantly trans conformation about C-O bonds. The proportion of PEO with this predominant configuration, termed TGT, was found to vary with coverage and temperature and was most prevalent for PEO-modified boehmite surfaces with a ligand coverage of approximately 0.95 at 18 degrees C. Dynamic water contact angle measurements showed that PEO-modified surfaces with the greatest proportion of PEO in the TGT configuration were also the most hydrophilic, thus indicating that PEO in the TGT configuration was more hydrated or polar than other configurations. Variation in the proportion of PEO in the TGT configuration with temperature and coverage have been used to explain the variable resistance to protein adhesion reported for PEO-modified surfaces. Factors influencing the configuration of surface-bound PEO with changes in ligand coverage and temperature have been discussed.