Silica 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 3.17 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. 

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... 

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... 

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... 

Figure 12. Influence of PVA immobilized onto nanosilica A-300 on RBC hemolysis as a function of PVA amount (last point corresponds to pure PVA solution without silica).

The aim of this contribution is to present experimental data concerning the synthesis, physicochemical properties and bio-activity of several nanosilica-based composites tested by interaction with native red blood cells (RBCs). The investigations include (i) synthesis of nanocomposites by adsorption of BSA, fructose and glucose on a fumed silica surface, and (ii) analysis of the adsorption properties of composites and their bio-activity. It is known that both glucose and fructose do not individually adsorb on fumed silica therefore, bovine serum albumin was used as a mediator to bind the monosaccharides to the fumed silica surface. 

Abstract. Adsorption of antioxidants (vitamins C and E) from aqueous and ethanol solutions on unmodified and partially hydrophobized nanosilica A-200 was studied using UV spectroscopy and quantum chemical methods with consideration for the solvent effects. Antioxidant power of silica nanocomposites with immobilized vitamins was evaluated by measuring the total polyphenolic index following the Folin-Ciocalteu method. It has been shown that immobilization of vitamins on silica surface leads to their stabilization. Being released from the carrier molecules of vitamins do not lose their antioxidant properties... 

To obtain silica nanocomposites with immobilized antioxidants, and to test their antioxidant activity, vitamins C and E were adsorbed onto nanosilica from ethanol solution containing both vitamins. A desorption experiment was then carried out. After the desorption of ascorbic acid from modified silica (0tms -0.40) into aqueous medium, the solvent was changed and the desorption of vitamin E into ethanol was studied. As one can see (Figure 6), both vitamins can be released from the surface for 1-2 hours. It should be noted that no increase in vitamin C concentration was detected in aqueous solution after its contact with A-200 for more than 30 min. Thus, as is the case for vitamins Bj and B6, desorption of vitamin C from the surface of modified silica is slower in... 

The use of nanosilica particles as drug carriers raises questions concerning the nature of forces controlling the adsorption interaction of cells with Si02 nanoparticles.15 The average diameter of human erythrocytes is 7500 nm16 while typical dimensions of silica nanoparticles with specific area of 200 to 300 m2/g commonly used for water dispersions are from 20 to 10 nm, with dissipation of 4 to 17 nm (within a 90 per cent interval).2,8... 

Sun et al. (2006) examined the use of novel silica nanofillers in underfill for flip-chip applications, and showed that pre-cure rheology and post-cure values of Tg are effected by nanosilica surface treatment. 

Surface properties of nanoparticles and the character of the polymer matrix determine their interactions and contribute to overall change in conductivity. Lower compatibility of nanoparticles and polymer matrix results in a disorder increase lower crystallinity of the matrix and vice versa, as Lopez et al. (2010) found in nanocomposites of methacrylates to which silica nanoparticles were added. Hydrophobic, (dimethyldichlorosilane)-modified nanosilica produced greater changes in dielectric relaxations than umnodified, hydrophilic silica that was more compatible with the polar polymer matrix. Radiochemical changes in nanoparticles like anion formation in nanotitania... 

In another study, where silver atoms were obtained by the reduction of silver ions originating from silver perchlorate (AgC104), particles were deposited on the surface of a colloidal (3-amino-propyl) trimethoxysilane (APS) functionalized nanosilica (Figure 20.7). The authors reported that the presence of metallic silver particle induced effective further depositiou of silver particles on the same silica particle (Zidki et al. 2007). 

Blending is generally just mixing of the silica nanoparticles into the polymer sol-gel process can be done in situ in the presence of a preformed organic polymer or simultaneously during the pwlymerization of the monomer(s) and in situ polymerization involves the dispersion of nanosilica in the monomerfs) first and then polymerization is carried out. 

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