Nanofiller composites

S.H. Mahmoud, A.E. El-Embaby, A.M. Abdallah, H.H. Hamama, Two-year clinical evaluation of oimocer, nanohybrid and nanofill composite restorative systems in posterior teeth, J. Adhes. Dent. 10 (2008) 315-322. 

W. Dresch, S. Volpato, J.C. Gomes, N.R. Ribeiro, A. Reis, A.D. Loguercio, Clinical evaluation of a nanofilled composite in posterior teeth 12-month results, Oper. Dent. 31 (2006)409 127. 

General background on polymer blend/nanofiller composites... 

Figure 5.1 Schematic illustration of polymer/layered nanofiller composite morphologies.

Mishra, T. K., A. Knmar, V. Verma, K. N. Pandey, and V. Kumar. 2012. PEEK composites reinforced with zirconia nanofiller. Composites Science and Technology 72 (13) (Angnst) 1627-1631. doi 10.1016/j.compscitech.2012.06.019. http //linkinghnb.elsevier.com/ retrieve/pii/S0266353812002436. 

Ghose, S., Watson, K.A., EUiott, H.A., Working, D.C., Criss, JM., Dudley, K.L., Connell, J.W., 2006. Fabrication and characterization of high temperature resin/carbon Nanofiller composites. In ASME 2006 Multifunctional Nanocomposites International Conference, pp. 69-77. 

One of most recent innovations in composite resins has been the development of nanofil composites, containing nanoscale particles ranging liom 1 to 100 nm with a more homogenous size distribution. The increased filler content results in a lower amount of resin, which may significantly reduce polymerization shrinkage and improve the physical performance of nanocomposites [52]. Further details on the advantages of nanocomposites are presented in Sect Nanocomposites . 

A major aim to prepare the polymer-nanofiller composites is to enhance the thermal stability of the materials. The thermal properties of polymer nanocomposites are usually evaluated by differential scanning calorimetry (DSQ and thermogravimetric (TG) analyses. From DSC and TG testing, the glass transition temperature (Tg) and decomposition temperature can be determined, from which the thermal properties of polymer nanocomposites can be evaluated. 

Improving the mechanical performance of the polymer is an important target of preparing the polymer-nanofiller composites. The storage modulus is one of... 

In this simple form, this expression is a good first approximation to compare the experimental reinforcement achieved upon addition of filler to the matrix, to the theoretical prediction [11]. It provides a measure of how efficiently the properties of the nanofiller are exploited in the composite, but also enables the comparison with the level of reinforcement achieved using other fillers. Note, in addition, that equation (8.2) sets an upper limit between Efl5 = 200 GPa and / = 1000 GPa, depending on whether the nanocarbon is randomly or perfectly oriented (without taking q0 into account). 

Where a is the composite conductivity, a0 a proportionally coefficient, Vfc the percolation threshold and t an exponent that depends on the dimensionality of the system. For high aspect ratio nanofillers the percolation threshold is several orders of magnitude lower than for traditional fillers such as carbon black, and is in fact often lower than predictions using statistical percolation theory, this anomaly being usually attributed to flocculation [24] (Fig. 8.3). 

Interfacial structure is known to be different from bulk structure, and in polymers filled with nanofillers possessing extremely high specific surface areas, most of the polymers is present near the interface, in spite of the small weight fraction of filler. This is one of the reasons why the nature of the reinforcement is different in nanocomposites and is manifested even at very low filler loadings (<10 wt%). Crucial parameters in determining the effect of fillers on the properties of composites are filler size, shape, aspect ratio, and filler-matrix interactions [2-5]. In the case of nanocomposites, the properties of the material are more tied to the interface. Thus, the control and manipulation of microstructural evolution is essential for the growth of a strong polymer-filler interface in such nanocomposites. 

Rubber-based nanocomposites were also prepared from different nanofillers (other than nanoclays) like nanosilica etc. Bandyopadhyay et al. investigated the melt rheological behavior of ACM/silica and ENR/silica hybrid nanocomposites in a capillary rheometer [104]. TEOS was used as the precursor for silica. Both the rubbers were filled with 10, 30 and 50 wt% of tetraethoxysilane (TEOS). The shear viscosity showed marginal increment, even at higher nanosilica loading, for the rubber/silica nanocomposites. All the compositions displayed pseudoplastic behavior and obeyed the power law model within the experimental conditions. The... 

Gersappe [250] used an MD simulation to probe the molecular mechanisms by which nanofillers reinforce the polymer matrix. Liao and Li [251] used Molecular Modeling to quantify CNT-polymer interfacial shear stress and found it to be about one order of magnitude higher than that of microfiber-reinforced composites. 

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