The effect can arise from interactions between the filler and different regions in the polymer matrix, such as tie molecules and truly ammorphous regions. This interaction may increase free volume in the polymer, thus lowering Tg.
Have you noticed a trend in this phenomenon for a series of nanocomposites with increasing ammounts of filler, for instance?
Another option is that the Tg is reduced due to the fact that the sizes of the polymer domains are reduced to small values. It is known that the Tg-s of thin polymer films (nm-range) are also smaller than in thick polymer films of exactly the same polymer.
But this behaviour occurred only when acid treated carbon nanotubes added.
Also , yes , degree of crystallization decreased but I think if degree of crystallinity decrease , tg should be increase or does not change at least. ?
to me this is quite obvious. The nanofiller produces a lot of interface, it creates surface and Tg will reflect the Tg of a surface of a polymer which is also lower than bulk Tg. I am very interested in experimental data on nano filled polymers, if you can send me any as I am intending to write a review on Tg (still ill understood or ill interpreted at the fundasmemntal level) [email protected]