Fillers nano, mobility

All the above studies demonstrate that low particle-particle attraction and strong filler/ma-trix interaction would provide nano-silica with sufficient mobility during drawing treatment. 

In the case of rubber blend clay composites good state of exfoliation of the clay, sufficiendy strong filler-rubber interactions as well as the compatibility between different rubber phases are playing major role. The presence of intercalated organoclays restricts the mobility of the rubber chains due to their confinement between the layers. As the concentration of nano filler increases the loss modulus increased. This can be explained in terms of the friction between the filler particles and the rubber matrix when the filler particles are uniformly dispersed in the mbber matrix. The damping values are found to decrease with the amount of filler due to the restricted mobility of the polymer chains owing to the intercalation of polymer chains into the layers of silicates. 

In this contribution, a brirf review of selected results was presented on the elastic and viscoelastic behavior of amorphous polymer nanocomposites. The ovei-view was done in a simplified manner, in order to support its miderstaudability. Below the matrix Tg, a nanocomposite behaves like a two component system due to the low-entropy/low-mobility state of polymer matrix. Above the mati-ix Tg, the polymer chains near the nano-filler surface become perturbed in respect to their dynamics. These changes occurring on the molecular level cause severe effects observable on micro- and macroscopic levels. Due to the extensive nanofiller surface area, the filler nanoparticles are able to cause these effects even at a very low filler concentration. Interestingly, the immobilization phenomenon in polymers filled with high specific surface area fillers has already been addressed in the 60s by DiBenedetto [40], Lipatov [44,56] and others [39,43,45]. The cited authors interpreted the results properly although very poor computer simulation possibilities were available at that time. 

In summary, even though an increase in toughness of some polymer/clay iianocomposites was achieved, the results are not always consistent. Especially, the role of polymer matrix plastic deformation versus nano-filler mobility is a critical issue that needs further detailed studies. 

Positron annihilation has been proven to be an effective tool to probe the interfacial characteristics of polymer nanocomposites. Zhang et al. used positron annihilation to study structures of melt-compounded HDPE/CaCOj nano-compositites in which nano-CaCOs fillers were treated with a coupling agent. A rapid decrease of free-volume concentration with increasing nano-CaCOs weight fraction was observed. An interfacial layer between the nano-CaCOs fillers and HDPE was also detected, which verified that die interactions between the nano-CaCOs and HDPE matrix indeed restricted the chain segmental motion and reduced the mobilization of polyethylene chains. 

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