Mechanism of Electrodeposition Process of Poly(Ethylene Glycol) Diamine to Titanium Surface

Electrodeposition of biofunctional molecules is effective in adding biofunction to metals; however, the mechanism of electrodeposition remains unclear. We consider the electrodeposition process of poly(ethylene glycol) (PEG) to the pure titanium surface, in which the termination of both PEG terminals proceeds with NH2 (PEG-diamine; MW: 1000). To elucidate this process, the thickness and mass change of the deposited layer and the electron transfer during electrodeposition was investigated using quartz crystal microbalance (QCM), ellipsometry, and cyclic voltammetry. Consequently, surface electric charge directly influenced the adsorption of PEG-diamine and unmodified PEG molecules. PEG-diamine was attracted to QCM electrode containing Ti (Ti-QCM electrode) and condensed on the surface by cathodic charge, by which electron transfer from PEG-diamine to the Ti surface occurred. Bonding of PEG-diamine with the Ti surface by electrodeposition was strong with no detachment from Ti. PEG-diamine was immediately adsorbed onto the Ti surface by the weak electrostatic force and bonded randomly via this force. Subsequent rearrangement and condensation occurred alongside a electrochemical reaction between the molecules and the Ti surface due to cathodic charge. Consequently, PEG-diamine molecules do not firmly remain on the Ti surface under electrodeposition, but shake near the Ti surface while undergoing repeated ionization and un-ionization.