Formation of Nanosized Phosphonic Acid Self Assembled Monolayers on Cobalt-Chromium Alloy for Potential Biomedical Applications

Abstract

Formation of nanosized self assembled monolayers (SAMs) of carboxyl terminated 16-Phosphonohexadecanoic acid (16-PA) and methyl terminated Octadecylphosphonic acid (ODPA) on Cobalt-Chromium (Co-Cr) alloy have been successfully demonstrated. Nanosized monolayers were formed by adsorption of these phosphonic acid SAMs on bare Co-Cr alloy by solution deposition technique. The formation of the nanosized monolayers was confirmed by using characterization techniques like Fourier Transform Infrared Spectroscopy (FTIR) with Attenuated Total Reflectance (ATR) attachment, Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), Ellipsometry and Contact Angle measurements. FTIR confirmed the SAM formation due to the presence of characteristic stretching vibration of SAM functional groups. FTIR studies suggest the binding of the phosphonic SAMs to be a combination of mono and bidentate binding. XPS showed presence of phosphorous peak and an increase in carbon peak intensity after SAM deposition, while it consequently showed decrease in peak intensity of the metal alloy (Co and Cr) peaks. AFM images gave good understanding of the topography, surface roughness and uniformity of SAM formation. Ellipsometric studies indicate nanosized thickness of the SAMs formed, while contact angle measurements showed changes in surface hydrophilicity/hydrophobicity after SAM formation. By tailoring the terminal functional group of these SAMs on Co-Cr alloy these nanosized monolayers could be potentially used for various biomedical applications such as localized drug delivery, biocompatibility, tissue integration etc.