Hierarchical nanocomposites properties

Most commonly used layered silicate is montmorillonite clay, which is composed of micron-sized particles. The particles are constructed of platelets with thickness of lnm and width of 100-200 nm. Platelets have permanent negative charge and they are held together by charge balancing cations such as Na" or Ca [2-i] ions. The significant disruption of individual silicate layers in polymer matrix with nanoscopic dimensions (exfoHated structure) leads to improvements of the nanocomposite properties. However, in many cases, the isolated silicate layers are not completely dispersed throughout the polymer matrix, instead, the clay particles in polymer matrix maintain the hierarchical architecture, and an interlayer expansion occurs (intercalated structure). 

The functions of the fourth hierarchical level are associated with capsulation of nanocomposites to maintain their properties and prolong the action of dmgs. Nanocapsulation is carried out with dextran, gelatin, polyvinyl alcohol, and polyvinyl pyrrolidone. 

Nam P. H. Okamoto M. Kotaka T. Hasegawa N. Usuki, A. A hierarchical structure and properties of intercalated polypropylene/ clay nanocomposites. Polymer, vol.42, (2001), 9633-9640... 

It is important to emphasize that many natural tissues are essentially composed of nanoscale biopolymers or biocomposites with hierarchical architectures. Therefore, by mimicking the structure and property of their natural counterparts, synthetic nanopoiymers and nanocomposites are very likely to enhance/regulate the functions of specific cells or tissues. This principle has been demonstrated by the success of bioinspired polymers and composites in both clinical practice and in laboratory research. In particular, bone is the hierarchical tissue that has inspired a myriad of biomimetic materials, devices, and systems for decades. This chapter focuses on this well-developed area of biomimetic or bioinspired nanopoiymers and nanocomposites for bone substitution and regeneration, especially those with high potentials for clinical applications in the near future. 

Wang Z, Li F, Eigang NS, Stein A (2006) Effects of hierarchical architecture on electronic and mechanical properties of nanocast monolithic porous carbons and carbon—carbon nanocomposites. Chem Mater 18 5543-5553... 

Nasegawa, H., Okamoto, H., Kawasiuni, M., Hasegawa, N., and Usuki, A. 2001. A hierarchical structure and properties of intercalated polypropylene/clay nanocomposites, h/mer 42 9633-9640. 

The CNT/polymer nanocomposites can be fabricated by means of solution blending, in situ polymerization and melt compounding [33-39]. The properties of CNT /polymer nanocomposites are directly related to their hierarchical microstructures. The processing conditions and polymers selected dictate the morphology, structure, electrical and mechanical properties of CNT/polymer nanocomposites. In addition, exfoliation and homogeneous dispersion of CNTs in the polymer matrix also play important roles in electrical properties of the composites. The agglomeration of nanotubes is detrimental to the formation of a conductive path network through the matrix of percolative CNT/polymer nanocomposites. 

As in the case of other material systems, the macroscopic properties of nanocomposites are driven by their micro-/nanoscopic structure. From an electrical insulation perspective, polyethylene (PE) and epoxy resins constitute two technologically important material systems, each of which embodies in very different ways, a great deal of structural complexity. In the case of PE, the constituent molecules are the result of the inherently statistical polymerisation process, which can ultimately result in the formation of a hierarchical morphology in which different molecular fractions become segregated to specific morphological locations. In an epoxy resin, the epoxy monomer chemistry, the hardener and the stoichiometry can all be varied, to affect the network structure that evolves. In the case of nanocomposites, another layer of structural hierarchy is then overlaid upon and interacts with the inherent characteristics of the host matrix. 

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]. 

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