Layered nanofillers graphene

The carbon-based nanofillers are mainly layered graphite, nanotube, and nanofibers. Graphite is an allotrope of carbon, the stmcture of which consists of graphene layers stacked along the c-axis in a staggered array [1], Figure 4.1 shows the layered structure of graphite flakes. 

Among nanofillers, carbon nanotubes (CNTs) have gained much attention because of their superior electrical, mechanical, and thermal properties. They are nanotubes, made by wrapped graphene layers, with a diameter of few nanometres, a length from a few microns up to millimetres, and a graphite-like structure. They can be single walled (SWCNT) or multi walled (MWCNT). In this paragraph, results refer to MWCNT, unless otherwise indicated. 

To achieve a lower percolation threshold and a high conductivity, more than one type of filler with different dimensions can be used to prepare CPCs, such as zero-dimensional atomic clusters (e.g., nano-carbon black, and silica), ID rod-like nanofiller (e.g., carbon nanotubes, and silver nanowires), and 2D layered nanofiller (e.g., clay platelets, and graphene) [ 106-110]. In fact, because of their differences in shape and element component, each nanoparticle has its own unique ability. Positive synergistic effects of these nanoparticles on improving the electrical and other properties of polymer matrix are expected. 

Graphene-polymer nanocomposites share with other nanocomposites the characteristic of remarkable improvements in properties and percolation thresholds at very low filler contents. Although the majority of research has focused on polymer nanocomposites based on layered materials of natural origin, such as an MMT type of layered silicate compounds or synthetic clay (layered double hydroxide), the electrical and thermal conductivity of clay minerals are quite poor [177]. To overcome these shortcomings, carbon-based nanofillers, such as CB, carbon nanotubes, carbon nanofibers, and graphite have been introduced to the preparation of polymer nanocomposites. Among these, carbon nanotubes have proven to be very effective as conductive fillers. An important drawback of them as nanofillers is their high production costs, which... 

During the last decade, nanofillers of different geometry, but in at least one dimension in the nanometer range, became more and more important. Examples are nanoclay (layered silicates, like montmorillonite), carbon nanotubes (single- and multiwalled), expanded graphite, and even graphene sheets. 

Lee S, Hong J-Y, Jang J (2003) The effect of graphene nanofiller on the crystallization behavior and mechanical properties of poly(vinyl alcohol). Polym Int 62 901-908 Lele A, Mackley M, Galgali G, Ramesh C (2002) In situ rheo-x-ray investigation of flow-induced orientation in layered silicate-syndiotactic polypropylene nanocomposite melt. J Rheol 46 1091-1110... 

Strength). The nanosized particles most commonly used in PU foams are clearly silicate-layered nanoclays, and particularly unmodified or organically modified montmorillonite (MMT), though others have also been considered, such as carbon-based nanofillers (carbon nanotubes and nanofibers, and more recently graphene), nanosilica, or cellulose-based nanofillers. 

Mechanical characterization under static loading of polymer-based nanocomposites has been widely studied in order to evaluate the influence of nanofiller content, dispersion, geometry, orientation, interfadal adhesion quality, and others on their mechanical performance. Layered silicates and CNTs are the most studied reinforcing agents in polymers due to their large aspect ratio and mechanical properties, but in the past decade particulate nanofillers such as sUica or functionalized graphene (FG) have received special interest. 

Silicone rubber (SR) nanocomposites with different dimensional nanofillers like OD (nanosilica, POSS, metal nanoparticle), ID (CNT, CNF), 2D (layered silicate, LDH, graphene) and 3D (graphite), etc., have been effectively reviewed in the up-to-date research work presented in this chapter covering their synthetic method, nanostructure and properties. It is noted that the SR nanocomposites exhibited improved mechanical, thermal, gas barrier properties, reduced flammability and biological properties at very low loading of fillers. However, it is concluded that such improvement in properties is only observed when fillers are uniformly dispersed and interact with SR chains. 

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