In the past few months our team has been searching for the best methods to polymerize our monomers of choice (TMA/CAA, TMA/SA, SBMA) on aluminum 6061. Once polymerized, a gel layer is formed over metal, but polymer gels like ours don't innately "stick" or bind to metal. Think of jello on a plate, we want to find a way to make sure our gel doesn't slide off our metal.
First tests took place in January and showed that directly placing our monomers on aluminum caused all the polymers to float off the metal once placed in water. Our team decided to implement using a silane initiator. What this initiator does is modify the surface of the metal by creating reactive groups off the metal to allow the polymer coating to bind. Since the initiator binds to both the metal and the polymer our hope was that the gels would stop separating from the metal, and it worked!(to a degree).
Our first tests with the silane initiator showed that much of the polymer gel coating for TMA/CAA lifted off the aluminum piece but a thin layer stayed bound to the metal. With SBMA we found that none of the polymer layer lifted and that the coating was uniform and stable in water for 30 days. When it came to our TMA/SA monomer we found that all our polymer coating lifted off the metal, and we would have to find another method to make our coating stable. With each test we learn important information on how our polymer coatings act, whether or not the result was what we are hoping for or not.
Our last test used and increased silane initiator concentration. We found that at a higher concentration of the initiator, the TMA/SA polymer was able to bind to the metal and be stable in water for two weeks, the only issue was that the surface of the polymer was not smooth. We want each coating to be smooth so we don't introduce a rough surface where bacteria have an easier time growing. So, as we have found ways to bind all of our polymer coatings to aluminum, we are looking into ways to now make these coatings smooth and optimize them for long term stability. Over the next few weeks our team will be looking into ways to characterize these coatings and make sure we are getting consistent results.
Below is a picture of some of our coatings after using the silane initiator for the first time. On the top we have TMA/CAA which binds mostly to the middle. On the bottom left is SBMA which has a very even and smooth coating covering the whole coupon, and on the bottom right is our TMA/SA which has no coating left after being in water for a day.