Nanosilica

The nanosilica-filled mbber composites show a steep rise in the tensde strength. This is principaUy due to better dispersion of silica in comparison to precipitated sdica within the mbber matrix. This is clearly demonstrated through the SEM pictures presented in Figure 3.8. 

Dispersion of nanosilica within the mbber matrices usually generates optically transparent materials. All the ACM-silica and ENR-sihca hybrid composites are completely transparent up to 50 wt% of TEOS concentrations. EoUowing are the figures (Figure 3.9) which show the visual appearance of the representative hybrid nanocomposites. The logos over which the films (average film thickness 0.25 mm) are placed are clearly visible. 

FIGURE 3.7 Comparative plots of tensile strength values of nanosilica and precipitated sihca-fiUed aciyhc rubber (ACM) composites. (From Bandyopadhyay, A., Bhowmick, A.K., and De Sarkar, M., J. Appl. Polym. Sci., 93, 2579, 2004. Courtesy of Wiley InterScience.)... 

Figure 3.17 shows the mechanical properties of the ACM-silica and ENR-silica hybrid composites synthesized from various pH, reproduced from the data reported by Bandyopadhyay et al. [36]. As morphology indicates, all the samples prepared within the pH range 1.0-2.0 are transparent, contain nanosilica particles, and are superior in tensile strength and modulus... 

Adsorption of rubber over the nanosilica particles alters the viscoelastic responses. Analysis of dynamic mechanical properties therefore provides a direct clue of the mbber-silica interaction. Figure 3.22 shows the variation in storage modulus (log scale) and tan 8 against temperature for ACM-silica, ENR-silica, and in situ acrylic copolymer and terpolymer-silica hybrid nanocomposites. 

Presence of nanosilica and its interaction with the rubber matrices strongly affect the low and high temperature degradation behaviour of the hybrid nanocomposites. Figure 3.24 shows the post-aging swelling analysis of the cross-linked ACM-sihca and ENR-silica hybrid nanocomposites. The data points are collected after aging of the samples at 50°C, 70°C, and 90°C for 72 h. 

Effects of nanoclay and silica in mbber matrices have been discussed in earlier chapters. Recently, several other nanofillers have been investigated and have shown a lot of promise. All these fillers have not been investigated on rubbers extensively, although they have great potential to do so in the days to come. In this chapter, we have compiled the current research on mbber nanocomposites having nanofillers other than nanoclay and nanosilica. Further, this chapter provides a snapshot of the current experimental and theoretical tools being used to advance our understanding of mbber nanocomposites. 

Abstract The supramolecular composites containing fullerenes C60 immobilized at nanosilica were used for the design of the molecular systems that can be an effective agent in cancer photodynamic therapy (PDT). In particular, it was shown that photoexcited fullerene C60-containing composites decrease viability of transformed cells, intensify the process of lipid peroxidation (LPO) in cell membranes and accumulation of low-molecular weight DNA fragments, and also decrease the activity of electron-transport chain of mitochondria. 

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... 

Choudhury et al. [86] have studied the effect of polymer-solvent and clay-solvent interaction on the mechanical properties of the HNBR/sepiolite nanocomposites. They chose nine different sets of solvent composition and found that chloroform/methyl ethyl ketone (Qi/MEK) (i.e., HNBR dissolved in Ch and sepio-lite dissolved in MEK) is the best solvent combination for improvement in mechanical properties. XRD, AFM, , and UV-vis spectroscopy studies show that the dispersion of clay is best in the Ch/MEK solvent combination and hence polymer-filler interaction is also the highest. images shown in Fig. 14a, b clearly elucidate the aforementioned phenomena. Consequently, the tensile strength and modulus are found to be higher (5.89 MPa and 1.50 MPa, respectively) for the Ch/MEK system due to the minimum difference in interaction parameter of HNBR-solvent (xab) and sepiolite-solvent (Xcd)- Choudhury et al. have also studied the effect of different nanoclays [NA, , 15A, and sepiolite (SP)] and nanosilica (Aerosil 300) on the mechanical properties of HNBR [36]. The tensile... 

In order to prepare ENR/silica nanoscale organic-inorganic hybrid composites, nanosilica has been generated by the sol-gel technique using TEOS as a precursor. Their effect on mechanical properties of the resultant nanocomposites have been... 

Table 5 Properties of maleated EPM-based TPVa at various nanosilica concentrations...

In order to produce high-performance elastomeric materials, the incorporations of different types of nanoparticles such as layered silicates, layered double hydroxides, carbon nanotubes, and nanosilica into the elastomer matrix are now growing areas of rubber research. However, the reflection of the nano effect on the properties and performance can be realized only through a uniform and homogeneous good dispersion of filler particles in the rubber matrix. 

Keywords nanosilicas structural and adsorption characteristics surface charge density aqueous suspension particle mobility protein adsorption Proteus mirabilis... 

Various nanosilicas (pilot plant at the Institute of Surface Chemistry, Kalush, Ukraine) were used as the initial materials (Table 1). 

The specific surface area (Sbet) °f silicas produced by burning of SiCl4 in an 02/H2/N2 flame can be varied over a large range from 50-500 m2/g (Table l).6,7 Features of the flame synthesis and the nature of amorphous nanosilicas cause certain generic characteristics (i) a roughly spherical shape of nonporous... 

The structure of secondary particles of nanosilicas is random and loose with an empty volume V, = pbx - pbx > 10 cm3/g.6"9 Changes in synthesis conditions allow one to vary the structure of contacts between adjacent primary particles in aggregates6,7, which affect the properties of powders and dispersions. Different treatments of the powders and suspensions result in changes in particle-particle interactions in aggregates, that leads to variation of the adsorption capacity for various adsorbates.1 16 From the textural characteristics (Table 1 and Figure 1) one can surmise that the structures of... 

Figure 1. (a) Nitrogen adsorption-desorption isotherms and (b) incremental pore size distribution (calculated using a mixture of cylindrical pores and gaps between spherical particles) of nanosilicas. 

---