I find the transparent polymer film, such as PMMA and PE, will get yellowish after metal deposition? Does anybody know the reason? Is it due to the thermal or photo-oxidation? If I want to get a transparent polymer film with high reflectivity silver layer, doesn't anybody know how to do it? Thank you.
Dear all, thank you for answering my question.
1. I also check the literature about the yellowing problem. The degradation should be the reason for the yellowing. Actually there are two possible mechanism: photo-oxidation or thermal oxidation. When temperature increases, the photo-oxidation will be accelerate. But it is difficult to distinguish photo-oxidation and thermal oxidation. Does anybody know which kind of by-product has the shift absorption? Is there any method to identify it?
2. Does anybody have experience about metallization on this transparent film without yellowing issue? I have tried thermal and e-beam evaporation. The one from E-beam evaporation is worse then that from thermal evaporation. I think photo-oxidation is attributed more than thermal-oxidation.
BOUAZIZ, Michael and Benalia,
I think you are right. The degradation should be the problem. I tested the UV-VIS spectroscopy and find the absorption increases a lot between 400 and 500nm. Do you have any experience to get avoid of thermo- or photo-oxidation during the metalization process? Thank you.
Gustavo,
Yes, I tried them both. E-beam is even worse than thermal. I think photo-oxidation accelerates while temperature increased.
Junggyu,
I will deposit enough thick silver on the polymer. I will test the reflectivity from the polymer side. The color issue is not from optical interference effect.
Generally, The reflection color of film will be changed due to reflective index. If thin film metal will be deposited on polymer film, the reflective light will be changed due to the thickness of metal films and also will be able to be changed the thickness of polymer film. I don't understand what phenamenon will be held in this evaluation.
your sight direction
thickness of film
which metal will be deposited?
You can calculate the thickness of metal for transparent film when considering absorption coefficient of deposited materials easily...
Dear all,
yes possible thermal oxidation may be the reason behind such a change in the transparency of the films mainly for PE. If I remember well it is the Norrish type 2 that applies. For the photo-oxidation this is also possible but after a prolonged time of exposure (under normal light). Regards
Form my opinion it is a absorption of blue/violet light resulting I a yellowing of the film. It's more like a shift in absorbance from UV to visible. Excess of photo initiator often results in this effect but heat and light also result in this effect as Bouaziz correctly explained. You may perform Uv-vis measurements which are less influenced by the subjectivity of the human eye. We are very sensitive for even slightly yellowing.
Article Synthesis and testing of ZnO nanoparticles for photo-initiat...
I worked with polymers a few years ago i would go for the absorption shift as well. But one think you can test, deposit the metal layer using different methods. A thermal evaporation of metal is quite different than e-beam evaporation. The second one will have plenty of UV to damage the polymer, while this first one will have more IR. Good luck.
The thermal oxidation may be the reason for this change in the transparency of the film.
Dear all, thank you for answering my question.
1. I also check the literature about the yellowing problem. The degradation should be the reason for the yellowing. Actually there are two possible mechanism: photo-oxidation or thermal oxidation. When temperature increases, the photo-oxidation will be accelerate. But it is difficult to distinguish photo-oxidation and thermal oxidation. Does anybody know which kind of by-product has the shift absorption? Is there any method to identify it?
2. Does anybody have experience about metallization on this transparent film without yellowing issue? I have tried thermal and e-beam evaporation. The one from E-beam evaporation is worse then that from thermal evaporation. I think photo-oxidation is attributed more than thermal-oxidation.
BOUAZIZ, Michael and Benalia,
I think you are right. The degradation should be the problem. I tested the UV-VIS spectroscopy and find the absorption increases a lot between 400 and 500nm. Do you have any experience to get avoid of thermo- or photo-oxidation during the metalization process? Thank you.
Gustavo,
Yes, I tried them both. E-beam is even worse than thermal. I think photo-oxidation accelerates while temperature increased.
Junggyu,
I will deposit enough thick silver on the polymer. I will test the reflectivity from the polymer side. The color issue is not from optical interference effect.
I thought that a chemical reduction should be possible (silver mirror to prove the presence of aldehydes is well known.). Following to Saechtling (textbook of plastics processing) “… deposition of Au, Ag and Cu by chemical reduction (using formaldehyde) from metal salt solutions” is possible. In your chase the salt is AgNO3. It might be possible that you will not find a detailed instruction dealing with PE and PMMA because this kind of modification is quite expensive (>> 15 EURO/m²[Domminghaus]).
Following to Domminghaus also a textbook of plastic processing high vacuum metal deposition following to norm VDI/VDE 2421 (02.80) for PE and PMMA is possible (that means the parameters have to be carefully chosen).
http://www.hanser-fachbuch.de/buch/Saechtling+Kunststoff+Taschenbuch/9783446434424
http://www.springer.com/us/book/9783642161728
Dear Yao Zhai,
first of all you should blame Einstein for his theory of relativity which leads to a relative mass of the electron... Than you should consider the island-like growth of the metal layer (up to the certain thickness, which you did not specify). It is well known that island of metals (in the nanoscale) can exhibit the plasmonic effect. Especially silver and gold which can appear in different colours depending on the thickness of the layer. In early 1900s there were papers published by Mie and Drude concerning abnormal properties of metals in different lengthscales. I think you will find them very informative. Moreover, I'm sure that "Physical chemistry" by Atkins will help you understand the basic concepts of the topic. If you will have further questions please do not hesitate to ask :)
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