Study of the formation of self-assembled monolayers on nitinol.

Shape memory alloys such as nitinol (NiTi) have gained interest due to their unique and unusual properties of thermal shape memory, superelasticity, and good damping properties. Nitinol is mainly used for medical purposes. In order to control the surface properties of this alloy, self-assembled monolayers (SAMs) were formed and characterized on the native oxide surface of nitinol for the first time. Factors which affect the formation of SAMs, such as head group functionality, chain length, and tail group functionality, were varied and analyzed. Functionalized alkyl phosphonic acid molecules (OH, COOH, and CH3) formed monolayers on the nitinol surface using a simple deposition method resulting in the molecules being ordered and strongly bound to the surface. Diffuse reflectance infrared spectroscopy (DRIFT), contact angle goniometry, atomic force microscopy (AFM), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) were used to characterize the surfaces before and after organic modification.