**1. Introduction**

In modern technology, composites are one of the most essential materials, which are the aggregate of two or more materials having different physical and chemical properties discriminated by their interface. Therefore, unlike the individual materials, the composite materials exhibit a distinctive property [1]. Mostly composite materials consist of at least two components including a continuous matrix phase and discontinuous reinforcement material while the other consists of one or more discontinuous phases dispersed in one continuous phase. Generally, a discontinuous phase has more advanced mechanical properties than a continuous phase. Continuous phase is known as "matrix" while discontinuous phase is called "reinforcement" or reinforcing material. Based on the size of reinforcement in the structures, composites are commonly divided into three basic classes, named macrocomposites, microcomposites,

and nanocomposites. Nanocomposites offer excellent features by the application of reinforcement in the composite below 100 nm in size phase [2].

#### **1.1 Nanocomposites**

Nanocomposites are multi-phasic materials, in which at least one phase show dimensions in the nano range (10–100 nm). In nanocomposites, interaction between matrix and reinforcement is very high due to high surface-to-volume ratio. The improved properties of nanocomposites depend on properties of each material, their relative amounts, and the overall geometry of the nanocomposites. Various materials possess different properties which when combined results in the formation of new material with additional advantages relevant to different areas of science and technology. They have high thermal and mechanical stability, multifunctional capabilities, chemical functionalization, and huge interphase zone. Generally, the nanocomposites show enhanced properties, such as high specific stiffness and strength, high toughness, low density, corrosion resistance, and thermal insulation [3]. Currently, nanocomposite materials have emerged as a suitable choice to overcome restrictions of different engineering materials. The amalgamation of nanoparticles into a matrix of materials like polymer, metal, or ceramics promote their properties such as excellent mechanical stability (in terms of strength, dimension stability, toughness, flexibility, Young's modulus, etc.), good optical activities, flame retardancy, low water/gas permeability, and high electro-thermal conductivity [4]. Nanocomposites are accepted at both the academic and industrial levels due to their extraordinary properties, distinctive design capacity, eco-friendly nature, easy fabrication, and cost-effectiveness. Nanocomposites have been commonly used in numerous applications due to their advanced properties. They are reported to be the materials of the 21st century in the vision of possessing design uniqueness and property permutation that is not found in conventional composites [5].

### **2. Carbon nanostructures**

Carbon-based materials have a huge stimulus in encouraging the improvement of society due to their abundance on the earth and environmental kindliness and other merits. Over the past few decades, carbon materials such as CNTs and graphene class of materials have seen incredible growth due to the discovery of advanced nanostructures. The innovation and study of carbon nanofillers have played a major role in the development of nanocomposites. Based on their dimensions, researchers classified materials as zero-dimensional (0-D) nanoparticles or quantum dots, one-dimensional (1-D) nanobelts, nanowires or nanotubes, two-dimensional (2-D) nanoplates or nanodisks, and three-dimensional (3-D) nanocones or nanocoils as shown in **Figure 1**. The nano-structured materials (NSMs) have drawn extreme interest due to their structure, surface area, size effects, and considerably improve the performance of the composites [7]. Carbonaceous nanofillers such as carbon nanotubes (CNTs) and graphene play a potential role as compared to others due to their improved structural and functional properties such as high aspect ratio, high mechanical and electrical properties, etc. [8]. In the last few decades, CNTs and graphene have been considered the most substantial nanofiller to formulate advanced nanocomposites for both academic and industrial fields due to their several potential applications. The combination of polymer nanocomposites with graphene-related materials (GRMs)

*Improved Nanocomposite Materials and Their Applications DOI: http://dx.doi.org/10.5772/intechopen.102538*

#### **Figure 1***.*

*Nano-carbon materials including 0D fullerene, 1D CNT, 2D graphene, 3D graphite, 3D graphene oxide, and 3D diamond are demonstrated [6].*

or carbon nanotubes (CNTs) has been discovered as a result of their low mass density and excellent mechanical properties for use in engineering materials for various challenging purposes [9].

#### **2.1 Carbon nanotubes**

CNTs are one-dimensional carbon materials that are different from other carbon compounds, such as graphite, diamond, and fullerene (C60, C70, etc.), having an aspect ratio greater than 1000 [10]. In 1991, Iijima discovered carbon nanotubes [11], which brought innovatory changes in the field of polymer nanocomposites. Ajayan et al. [12], reported the first carbon nanotubes reinforced polymer nanocomposites. Basically, carbon nanotubes are graphene sheets having hexagonal structures which are rolled up into cylindrical form and rounded off with half shape of fullerene structure. The two types of carbon nanotubes are the single-walled nanotubes (SWNTs), which are single graphene sheets rolled into a cylinder and the other one is multiwalled nanotubes (MWNTs), in which numerous graphene layers are stacked into concentric layers in the form of cylinders with an interspacing of 0.34 nm (**Figure 2**). On the basis of atomic arrangement, the three types of structures are zigzag, armchair, and chiral (**Figure 3**) [13]. Properties of carbon nanotubes are greatly reliant on morphology, size, and diameter and maybe metallic or semiconducting depending on the atomic arrangement [14].

#### **Figure 2.**

*The conceptual diagram showing the general dimensions of the length and width of single walled carbon nanotubes (SWCNTs) and multi-walled CNTs (MWCNTs [13].*

#### **2.2 Graphene**

Graphene, a typical 2D material, has received incredible attention due to attractive features like very high specific surface area (2360 m2 g−1), highest strength (≈130 GPa) and Young's modulus (≈1.0 TPa), best known thermal conductivity (TC, ≈5000 W m−1 K−1), and electrical conductivity (108 S m−1). Therefore, graphene is the perfect nanofiller for improving the mechanical, electrical, thermal, and optical properties of polymers [15]. Through valuable interfacial stress transfer, graphene effectively improves the mechanical properties like tensile strength and Young's modulus of polymers [16, 17]. Graphene can competently strengthen brittle polymers by extending the crack propagation path in nanocomposite. The excellent electrical property of graphene can clearly improve the electrical conductivity of polymers for free electrons by building a conductive network [18]. The distinctive thermal conductance of graphene carries the excitement to formulate high-performance thermal conductive nanocomposites for application in high power density devices in thermal management [19, 20]. Due to distinct ultrahigh thermal conductivity, graphene is engaged to fabricate the thermal interface materials (TIMs) [21] and phase change energy storage composites (PCCs) [22].

*Improved Nanocomposite Materials and Their Applications DOI: http://dx.doi.org/10.5772/intechopen.102538*

#### **Figure 3.**

*Schematic representation of how a graphene sheet is rolled to form three chiralities of nanotubes: (b) zigzag, (c) armchair, and (d) chiral nanotubes [13].*

#### **2.3 Diamond**

Diamond is a three-dimensional carbon material with a crystal structure called diamond cubic. Diamond is an outstanding carbon material because of its inert nature, high-thermal conductivity, stiffness, biocompatibility, and optical transparency. Nanodiamonds (NDs) are advanced carbon nanostructures with sp3 hybridized carbon atoms bonded to form diamond-like cubic geometry. Their dimensions are in the range of 5 to 102 nm. Numerous properties of NDs are far better than bulk diamond and they present these properties on nanoscale [23]. The superior mechanical and thermal characteristics of ND make it a suitable nanofiller for carbon-based nanocomposites. The surface of common synthetic NDs has no functional groups. Nevertheless, an ND can be modified with a functional polymer or be functionalized with hydrogen/deuterium-terminated, halogenated, aminated, hydroxylated, and carboxylated by strong reagents and under severe conditions according to targeted applications and desired physicochemical properties [24].

#### **2.4 Fullerenes**

Fullerenes are a new class of carbon nanomaterials discovered in 1985 by Kroto et al. and get the Nobel prize award in chemistry for the year 1996 [25]. According to Mukherjee et al. the diameter of fullerenes nanomaterials is ≤1 nm [26]. The fullerene family includes several atomic Cn clusters (*n* > 20), composed of carbon atoms on a spherical surface. They are closed-cage carbon molecules containing pentagonal and hexagonal rings with sp2 hybridized carbon atoms bonded by covalent bonds. The carbon atoms are regularly arranged at the vertices of pentagons and hexagons surfaces. They have the formula C20+ m, with m being an integer number, and comprise a wide range of isomers and homologous series, from the most common and investigated C60 and C70 to the so-called higher fullerenes like C240, C540, and C720. The incorporation of fullerene nanofiller into numerous polymers has been achieved by physical and chemical methods [27]. In this way, the combination of distinctive features of fullerenes with physical properties of polymers may yield advanced polymeric materials with novel physicochemical characteristics. The attractive physiochemical properties of fullerene-based nanomaterials make them suitable materials to use in medicinal chemistry [28].
