Dear Omid,

silane coupling agents, like your, are widely used for the preparation of self assembled monolayers. When your oxidized steel substrate become in contact with the solution of the coupling agents, the silane head groups react with the substrate, bonding to them, leaving the amine tails to form a "barrier" that can improve or prevent your polymer to form any bond or strong interaction with your steel substrate, so facilitating the detachment of your polymer.

I think that the main factor that determine the adhesion is the funtional group at the end of the tail of the silane.

Without changing your silane coupling agent, you could try to cure in oven your metal/polymer system in order to strengthen the bonding interaction.

Have you verified that all the surface functionalities reacted with the coupling agent?

Dear Omid,

I am not able to give you the one explanation. E.g. Your procedure and question is not clear. Is your aim to modify the bare metal surface or the oxide. Salinization can often be the critical point (what kind of bond to you expect to take place), compare to page 17 of the Gelest catalog (You need stable and reactive OH functionalities for direct linking). You will also find on this page the statement "reactivity to the organic compound" of the silane.So, you have also to consider what kind of adhesive interactions are in-between the polymer and the metal/oxide before the modification and what kind of interactions after the modification. Polymer surface interactions are often strong. For PA6 you may find the necessary information in the second link. You can also try to preform CA or IR measurements to investigate the surface modification (as performed in our own studies).

http://www.gelest.com/goods/pdf/couplingagents.pdf

http://reltekllc.com/adhesivesfornylon.aspx

Thanks a lot for your guide Fabio

you said that "you could try to cure in oven your metal/polymer system in order to strengthen the bonding interaction", but there is no any connection between my polymer and metal that I want to cure in oven for strengthen  the bonding interaction.

what do you mean exactly for this guide?

many thanks

Dear Dr.Michael Schmitt 

I read an article mentioning this silane is suitable for making connection between stainless steel and thermoplastic polyurethane. So, based on this article I selected methoxy group for reacting with stainless steel and selected Amino group based on suggestion of Dow Corning Company for PA6. In this recommendation PA6 and Polyurethane are in the same row that functional group for this row is Amine.

I have prepared a brief report of what I  have done that is attached. now in your opinion which part of my procedure is wrong?

Dear Omid,

I apologize for the misunderstanding.

With the sentence you mentioned I didn't mean that you have a direct metal-polymer interaction, but, since you have coupled with the silane the steel surface and than you have coated it with your Nylon, an oven cure could help to improve the connection between your polymer and the silane-coupled steel.

As you probably know already, the interaction polymer-amine is probably due to the hydrogen bonding interaction with the oxygen of the amide function present in nylon and the hydrogens of the terminal amine groups of the silane; so the cure in oven, increasing the mobility, could leave to a better interaction.

Yes your procedure is wrong. You need to blast the SS with alumina, clean with Acetone and dry. make a mixture of 80% EtOH 20% water and 2% Silane. mix for 30 min. apply wait 1 hr. at RT, heat 60-90 C for 1 hr. then inject the PA. good luck!!