Adsorption of γ-mercaptopropyltrimethoxysilane on zinc: A study of the competition between thiol and silanol functions related to the age of the siloxane solution, its pH and the oxidation state of the surface

► We analyse the way of adsorption on Zn substrate of a bipolar coupling agent (γ-MPS). ► For neutral pH , only the SH function reacts with the Zn substrate. ► At acid pH either SH group or SiOH one chemisorbs onto the surface. ► Age of the solution and surface treatment determines the ratio of grafted poles.