Nanofillers dispersion

For appropriate comprehension of morphology and the concomitant structure-property correlations in nanocomposites, knowledge of the state and extent of nanofiller dispersion in the matrix is of paramount importance. Numerous methods have been reported in the literature in this regard, for instance, WAXD [6, 38], SAXS [8, 39], SANS [40], SEM, [6, 41], AFM [7, 42], HRTEM, STEM, EELS [43], SSNMR [44], EPRS [45], UV/vis/NIR, FTIR [46], Raman spectroscopy... 

A nanofiller disperse particle aggregation process in elastomeric matrix was studied. The modified model of irreversible aggregation particle-clusters was used for this process of theoretical analysis. The modification necessary is defined by the simultaneous formation of a large number of nanoparticle aggregates. The approach offered here, allows prediction of nanoparticle aggregates final parameters as a function of the initial particle size, their contents and a number of other factors. 

Due to the positive influence of these nanofillers in the nanocomposites, an abundance of articles on different methods to quantify the influence of the nanofiller can be found in the literature. Many articles on assessing the clay dispersion in a polymer matrix by morphological and rheological studies have been published. Due to the relatively easy sample preparation and sample loading, rheology is often used to screen or characterize the nanofiller dispersion, or more generally determine the influence of the... 

However, in both cases - thermoplastics and thermosets - the equipment and the processes need to be adapted to the nanosized fillers. The most crucial point in the production of polymer-nanofiller dispersions is the proper separation of the CNTs from each other, the deagglomeration of agglomerates, and their coupling to the polymeric matrix material. For this purpose, dispersion aids, stabilizers, and compatibilizers, used for other filler particles, need to be adapted in many cases specifically for nanosized fillers with their different surface treatments for the different matrix materials. This is a very complicated issue, and makes a close co-operation between the different scientific disciplines necessary [1]. 

In addition, by scaling the filler size to the nanometer scale, it has been shown that novel material properties can be obtained. Nanoscaled fillers are those having at least one dimension in the range of nanometers (< 100 nm) [3]. When the dimensions of the reinforcement approach the nanometer scale, a number of effects make the properties of the corresponding composites different from those of composites reinforced with micro-scaled fillers. The major influencing factors of the properties of nanocomposites are nanofiller dispersion, dimensions, volume fractions, nature of the matrix material, interfacial properties between filler and matrix, and manufacturing process [4]. 

The in situ synthesis of polymers in the presence of nanoclays can produce good nanofiller dispersions but is often difficult to control and its production times are relatively long. Melt processing is certainly the most interesting preparation method from an application and economical point of view since it can be readily implemented into traditional polymer processing routes and provide reliable and reproducible products. 

OC, G and CNTs were blended with rubbers and, in particular, with isoprene rubbers through emulsion, melt and solution blending. As mentioned above, the upper level of nanofiller organization refers to their distribution and dispersion in the rubber matrix. This section summarizes the effect of blending technology on nanofiller dispersion. 

The extent of nanofiller dispersion and matrix properties have a significant effect on the overall blend properties, for example, highly exfoliated MMT particles in the polyamide matrix can make it brittle, whereas partially exfoliated clay particles in extruder-made thermoplastic olefin nanocomposites can lead to significant improvements in impact strength depending on the PP molecular weight and elastomer MFI. 

The demand for material properties to meet superior and more severe specifications has motivated vigorous research on polymer nanocomposites, that is, polymer matrices incorporated with fillers with at least one dimension in the nanometer range. In a nutshell, these advanced materials exhibit enhanced thermal, mechanical, barrier, and fire retardant properties over virgin polymers [32-37], while their performance depends on the level and the homogeneity of nanofillers dispersion, as well as on the potential for interfacial bonding between the filler and the matrix. 

A number of methods have frequently been employed in the production of nanocomposite materials. These include solution intercalation, melt intercalation, polymerization, sol-gel, deposition, magnetron sput-tering, laser, ultrasonication, supercritical fluid, etc. In PHA nanocomposite fabrication, solution intercalation and melt intercalation methods are the most widely explored procedures. However, use of in situ intercalative polymerization, supercritical fluids and electrospinning are shown to be promising and emerging techniques. The performance and quality of a nanocomposite depends on how well the nanofillers disperse or blend into the matrix. Therefore, these methods constitute different strategies to improve the composites thermo-mechanical and physico-chemical properties by enhancing efficient interactions between the nanofiller and the polymer matrices. 

The use of toxie organometallic catalysts and initiators in polymerization, as well as bulk solvents for monomer solutions, are among the industrial limitations of the in situ intercalative polymerization method, despite its reported advantage of good nanofiller dispersion in nanocomposite production. ... 

Kochetov et al. (2012) described the dielectric response of a range of nanodielectrics based upon particulate nanofillers dispersed within an epoxy matrix. In all cases, with the exception of nano-silica, the inclusion of a low volume fraction (<5 %) of nanofiller resulted in a reduction in the measured real permittivity, below that of the host matrix, despite S In another epoxy-based... 

The general processing steps of pressure molding and sintering are described as follows. First, the PTFE and nanoscaled fillers were premixed according to a certain mass ratio that is varied with different nanofillers. The mixture of ITEE and nanoscaled fillers was then placed into a high-speed mixer and stirred for at least 2 h again to achieve more uniform nanofiller dispersion. Finally, the mixture was compression molded. A laboratory pressure of 40—50 MPa was held for approximately 30—45 min to ensure... 

The obtained composites have been analyzed by XRD and TEM in order to estimate the extent of the nanofiller dispersion in the PCL matrix. In all cases, intercalated nanocomposites were formed as evidenced by the significant increase in the interlayer distance. For instance, the interlayer distance increases from 1.17 nm to 1.79 nm for Cloisite Na -filled PCL composite (Figure 7). The intercalated nanostructures have been confirmed by TEM analysis. 

Functional polymer nanocomposites consist of polymer matrices, including thermoplastics, thermosets and elastomers having nanoparticles or nanofillers dispersed in the polymer matrix. Two or more materials are combined to produce composites that possess properties that are unique and cannot be obtained from the individual materials acting alone. This new class of composite materials has shown enhanced optical, magnetic, mechanical, electrical and dielectric properties. They are important commercial materials with new combinations of structural and functional properties for applications in medicine, civil engineering, rubber and plastics, automotive and electrotechnical industries [39]. 

Nanofillers dispersed in polymer matrices according to different approaches (a) blending and (b) copolymerization or condensation. 

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