Polymer nanocomposites continuous structures

FIGURE 4.2 Continuous structures of polymer nanocomposites. (A) SEM image of thermoplastic elastomer/CNT composite with CNT dispersed in polymer matrix. (B) SEM image of PPy/Au nanocomposite with ordered porous structure. (C) SEM image of P(VDF-HFP)/Si02 composite with porous structure. (D) TEM image of PEDOT/graphene composite with a multilayer structure. (A) Reproduced with permission from reference Koemer, H., Price, G., Pearce,... 

Nanocomposites consist of a nanometer-scale phase in combination with another phase. While this section focuses on polymer nanocomposites, it is worth noting that other important materials can also be classed as nanocomposites—super-alloy turbine blades, for instance, and many sandwich structures in microelectronics. Dimensionality is one of the most basic classifications of a (nano)composite (Fig. 6.1). A nanoparticle-reinforced system exemplifies a zero-dimensional nanocomposite, while macroscopic particles produce a traditional filled polymer. Nanoflbers or nanowhiskers in a matrix constitute a one-dimensional nanocomposite, while large fibers give us the usual fiber composites. The two-dimensional case is based on individual layers of nanoscopic thickness embedded in a matrix, with larger layers giving rise to conventional flake-filled composites. Finally, an interpenetrating network is an example of a three-dimensional nanocomposite, while co-continuous polymer blends serve as an example of a macroscale counterpart. 

The co-continuous structure and the final rheological properties of an immiscible polymer blend are generally controlled by not only the viscoelastic and interfacial properties of the constituent polymers but also by the processing parameters. For example, the effect of plasticizer on co-continuity development in blends based on polypropylene and ethylene-propylene-diene-terpolymer (PP/EPDM), at various compositions, was studied using solvent extraction. The results showed more rapid percolation of the elastomeric component in the presence of plasticizer. However, the same fuUy co-continuous composition range was maintained, as for the non-plasticized counterparts (Shahbikian et al. 2011). It was also shown that the presence of nanoclay narrows the co-continuity composition range for non-plasticized thermoplastic elastomeric materials (TPEs) based on polypropylene and ethylene-propylene-diene-terpolymer and influences their symmetry. This effect was more pronounced in intercalated nanocomposites than in partially exfoliated nanocomposites with improved clay dispersion. It seems that the smaller, well-dispersed particles interfere less with thermoplastic phase continuity (Mirzadeh et al. 2010). A blend of polyamide 6 (PA6) and a co-polyester of... 

The final properties of the cellulose nanofibers-based nanocomposites depend not only on the aspect ratio (1/d), but also on the mechanical and percolation effects [4, 24]. The developed studies have shown that the tensile properties and transparency of the nanocomposites increase with the aspect ratio of the cellulose nanowhiskers [25,26]. In addition [27], the tensile properties also depend on the orientation of the cellulose nanofibers inside the polymeric matrix, making critical the processing conditions. However, other authors [26] showed that filler orientation and distribution play an important role in the aspect ratio. The maximum enhancement in properties of the composites takes place for the adequate quantity of filler in the matrix, where the particles can form a continuous structure known as percolation threshold [28]. The improvement of the properties of nanocomposites compared with the neat matrix is also related with the dispersion of filler within the matrix. The compatibility between the selected matrix and the nanofiller is another important factor to be taken into accoxmt [29]. The high polarity of cellulose surface leads to certain problems when added to nonpolar polymer matrices including weak interfacial compatibility, poor water barrier properties and aggregation of fiber by hydrogen bondings [4, 30]. 

The remarkable properties of electrospun CNTs nanocomposites continue to draw attention in the development of multifunctional properties of nanostructures for many applications.. Multiscale model for calculation macroscopic mechanical properties for fibrous sheet is developed. Effective properties of the fiber at microscale determined by homogenization using modified shear-lag model, while on the second stage the point-bonded stochastic fibrous network at macroscale replaced by multilevel finite beam element net. Elastic modulus and Poisson s ratio dependence on CNT volume concentration are calculated. Effective properties fibrous sheet as random stochastic network determined numerically. We conclude that an addition of CNTs into the polymer solution results in significant improvement of rheological and structural properties. 

Due to the structure filler hierarchical morphology and surrounding polymer matrix at nanometer length scale, the well-defined concepts in conventional two-phase composites should not be directly applied to polymer nanocomposites. Polymer molecules and nanofillers have equivalent size and the polymer-filer interactions are highly dependent on the local molecular structure and bonding at the interface. Therefore, nanofillers and polymer chains structures cannot be considered as continuous phase at these length scales, and the bulk mechanical properties caimot be determined, for that reason, using traditional continuum-based micromechanical approaches [47,48]. 

Successful commercialization of low cost, high efficiency solar cell fabrication is highly dependent on fabrication methods that employ continuous processing techniques. One major issue encountered in solar cell construction is the adhesion of thin film solar cells on polyimide substrates. Another involves the adhesion between polymer nanocomposite solar cell structures. The examination of the adhesion promotion potential of variable chemistry atmospheric plasma surface modifications against wet primer chemistry in solar cell construction has shown that APT is a viable continuous and environmentally friendly processing alternative to batch plasma and surfactant-based surface modification protocols. 

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