The loss modulus divided by the elastic modulus is an easy way to compare materials. The tan_delta is indeed not dependent on the geometry of the sample. A better interface or the development of an interphase will reduce tan_delta. The amplitude is actually similar to the improvement in elastic modulus on the rubbery plateau, except it is much easier to measure and compare. In summary the creation of an interphase shall reduce the maximum of tan_delta In the alpha transition.

thanks for your comment.

i did acid cutting for fillers whcih i am  expecting that a good interaction between  polymer and filelrs ,  but the tan delta do not decrease much , is any idea please