Nanocomposites filler-matrix interphase

The unexpected beneficial behavior of nanocomposites is due to filler/matrix and filler/filler interactions. Owing to the huge specific surface of well dispersed nanoparticles, it is often quoted that the properties of nanocomposites are controlled by interface/interphase characteristics. The distinction between interface and interphase depends on whether or not this region has a finite thickness. Polymer nanocomposites are already commercialized, e.g., films of improved barrier properties and low-density injection moldable resins with high heat distortion temperature. Although the structure-property relationships in nanocomposites are poorly understood, the... 

This issue of specific surface area hints at how one might change the nature of reinforcement. In typical micro- and macrocomposites, the properties are dictated by the bulk properties of both the matrix and the flUer. This relationship between the properties of the composite and the properties of the filler is what leads to the stiffening and degraded elongation mentioned earlier. In the case of nanocomposites, the properties of the material are instead tied to the interface. Terms like bound polymer, bound rubber, and interphase have been used to describe the polymer at or near the interface, where significant deviations from bulk structure and properties are known to occur (Fig. 6.2). 

The sol-gel technique to generate nanosilica particles within a polymer matrix has been a useful process which gives specific interphase impact between the organic matrix and inorganic component. The incorporation of the filler particles into polymers using this process avoids the aggregation of the nanofiller within the polymer matrix [17]. The polymer-silica interaction depends on the size and shape of the nanofiller particles, their volume fraction, and the interparticle interaction [18]. What s more, these parameters also strongly influence the properties of the nanocomposites. 

Compared to microcomposites, where the mechanical behavior is mainly a function of the characteristics of filler and matrix and their respective concentrations, generally speaking, two major characteristics define the mechanical performance of polymer nanocomposites (8) the nanoscale size and geometry of the fillers (aspect ratio) and their dispersion into the polymer matrix, and the interaction between the polymer chains and said nanofillers (interphase). This section highlights the influence of these two factors on the mechanical behavior of polymer nanocomposites. 

The interaction between the matrix and the filler is the key to the optimization of the properties of polymer nanocomposites. Therefore, the performance of the nanocomposite is compromised by the state of dispersion of the filler and the nature of the interface/interphase with the host matrix. The aspect ratio and orientation of the filler or the changes triggered in the matrix morphology upon addition of the reinforcement are other important parameters that can significantly influence the composite properties [36]. 

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