Nanocomposite materials distribution

Due to their unique mechanical and electronic properties carbon nanotubes (CNT) are promising for use as reinforcing elements in polymer matrixes [1, 2]. The main problems are creation of strong cohesion of CNT with a polymer matrix and uniform distribution of CNT in matrix [3], The goals of this work were development of PTFE-MWNT nanocomposite material with high mechanical characteristics and investigation of influence of MWNT surface groups on mechanical and electronic parameters of the composite material. 

The nanotubes were first oxidized in nitric acid before dispersion as the acidic groups on the sidewalls of the nanotubes can interact with the carbonate groups in the polycarbonate chains. To achieve nanocomposites, the oxidized nanotubes were dispersed in THF and were added to a separate solution of polycarbonate in THF. The suspension was then precipitated in methanol and the precipitated nanocomposite material was recovered by filtration. From the scanning electron microscopy investigation of the fracture surface of nanotubes, the authors observed a uniform distribution of the nanotubes in the polycarbonate matrix as shown in Figure 2.3 (19). 

As for the linear properties, numerous approaches have been proposed to predict and explain the nonlinear optical response of nanocomposite materials beyond the hypothesis leading to the simple model presented above ( 3.2.2). Especially, Eq. (27) does not hold as soon as metal concentration is large and, a fortiori, reaches the percolation threshold. Several EMT or topological methods have then been developed to account for such regimes and for different types of material morphology, using different calculation methods [38, 81, 83, 88, 96-116]. Let us mention works devoted to ellipsoidal [99, 100, 109] or cylindrical [97] inclusions, effect of a shape distribution [110, 115], core-shell particles [114, 116], layered composites [103], nonlinear inclusions in a nonlinear host medium [88], linear inclusions in a nonlinear host medium [108], percolated media and fractals [101, 104-106, 108]. Attempts to simulate in a nonlinear EMT the influence of temperature have also been reported [107, 113]. 

It appears to us worthwhile to point out the different parameters relevant to the analysis of the tlrird-order nonlinear optical response of nanocomposite materials, because some of them are sometimes omitted in the literature, rendering the comparison difficult. They can be classified into two main sets. First, some parameters are linked wltlr the optical excitation source, which usually consists of a pulsed laser beam Wavelength X, pulse energy E, pulse duration t, repetition rate v. Secondly, otlrer relevant parameters concern the material Itself Particle size and shape (and distributions), metal volume fraction p, particle spatial arrangement in the host medium. 

To create nanocomposites materials with specific applications the nanoparticles dispersion control into the polymer matrices still remains a critical challenge for researchers. So, the development of nanocomposite materials requires control over nanoparticle distribution in the polymer matrix. Making connections between nanoparticle dispersion, enhanced the macroscale properties and evaluated the end of life of this materials is then a crucial aspects that is only now beginning to be considered by researchers around the world. So, make these connections is essential to better development and application of the nanotechnology in the near future. 

Despite considerable effort in the field, major challenges remain in the control of the homogeneity, loading, size, and distribution of the nanoparticies within the host inorganic network, which in turn determine directly the electronic, optical, magnetic, and catalytic properties of nanocomposite materials. 

Currently, numerous procedures for the preparation of nanocomposite materials are available. Recently, the major synthetic approaches (e.g., evaporation of elemental metal with its deposition on polymeric matrices, plasma-induced polymerisation, vacuum evaporation of metals, thermal decompositions of precursors in the presence of polymers, and reduction of metal ions using different procedures including electrochemical) have been surveyed in books and reviews. However, the uniform distribution of ingredients is generally difficult to achieve when hybrid nanocomposites are prepared with the use of the above-mentioned procedures resulting in the nonuniformity of the properties of the material. The following three principal procedures are most commonly employed ... 

The production methods of nanocomposite materials that are, by their essence, a polymer matrix, where nanoparticles and clusters are randomly distributed (a totality... 

In transmission electron microscopy (TEM), a beam of electrons is passed through a thin sample, such that an image is formed as a result of absorption or diffraction contrast. In the case of polymers, a combination of disorder and radiation sensitivity means that, of these, absorption contrast is most important, in which case, high resolution images can be generated where image contrast is based on the spatial variation in electron density. In the case of materials such as nanocomposites, the distribution of the nanoparticles can therefore easily be imaged, as a result of the difference in the atomic number between the nanoparticles and the matrix polymer, as shown in Eig. 2.18. 

Among the microscopic methods used for characterization of polymer/HAp systems the most important are SEM and TEM. TEM is recommended whenever an in-depth study is required and allows a qualitative understanding of the internal structure, spatial distribution of the various phases, and defect structure of nanocomposites through direct visualization. However, special care must be exercized to ensure that a representative crosssection of the sample is evaluated [325], 3D TEM is a recent development in the area of high-resolution electron microscopy - it allows visualization of the 3D structure of nanocomposite materials. 

The produced fibres were examined using SEM/EDS (Nova NanoSEM, FEI) method in order to determine morphology and distribution of the nanofillers. Changes in the materials structure caused by the presence of the nanofiller were assessed on the basis of thermal analysis methods (DSC/TG, STA 449F3, Netzsch). The measurements were performed in nitrogen atmosphere with temperature ramp 10 deg/min up to 600°C. The method was used to examine both the fibres and the prepared polymer foils. Comparison between results of the thermal analysis of the polymer foils and the electrospun fibres allowed to asses the influence of the forming method on structure of the nanocomposite material. 

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