How about glass nanoparticle? 3M has some glass nanobubbles to sell which may help you.

Dear Xiguang,

I tried with hollow glass spheres from 3M but the dispersion into the polymer matrix was difficult. Now i am in the process of making the composites with the same. if any other suggestions are there, then you can share. Thanks for your reply.

Personally I guess you may need to do some surface modification of galss bubble. Make sure the surface of glass have good interaction with PU you used. Contact 3M to see if they can provide you more information

You may also try Barium sulphate as a "heavy" filler.

http://www.phantomplastics.com/attachments/File/Introduction_to_Filled_Thermoplastics.pdf

http://wings.buffalo.edu/eng/mae/cmrl/Structural%20composite%20materials%20tailored%20for%20damping.pdf (it is a review)

http://books.google.hu/books/about/Sound_and_vibration_damping_with_polymer.html?id=iIpRAAAAMAAJ&redir_esc=y

Good luck

I would recommend to modify the glass particles with a polymer coating. We did a study in that direction. Have a look at the paper on this easy coating process we report of:

Kuttner, C.; Tebbe, M.; Schlaad, H.; Burgert, I.; Fery, A. Acs Appl Mater Inter 2012, 4,

3485–3492.

And about the embedding, maybe have a look at DOI: 10.1021/am302694h

Dear Gyorgy & Christian thanks a lot for your suggestions. I will be working on the specified matters.

Good luck Sarojini. Feel free to contact me if you need more information or support with the surface modification.

Sarojini, you can use any platelet material like mica, graphite, micro glass flake or combinations there off. The noise dampening effect is based on having shear forces between the visco-elastic matrix and the surface of the platelets. Use of micro glass bubbles will give you no increased damping compared to air bubbles. You also need to tell us what you really are trying to achieve. Will the coating be applied on a stiff material like metal or is it to fill cavity walls or whatever.

Also the most important factor in noise damping is to have a resin matrix with a glass transition exactly at the operating temperature. My comments are related to noise dampening of vibrational energies in metal layers. If you are merely talking about sound insulation then a thin layer with a heavy mass will be the better solution. In such a case you should use barium sulfate or micaceous iron oxide.

If you want to go for natural materials, saw dust (fine particles preferable) is also very good damping material.