Spherical nanosilica

Recently it has also been shown that modified spherical nanosilica particles can be used to toughen epoxy resins without the loss of other properties, such as glass transition temperature or modulus.28 When such surface modified nanoparticles are added to CTBN toughened epoxy resins, the performance of both one- and two-component epoxy adhesives was greatly improved. 

At present, clays are by large the most investigated nanofillers in flame retar-dancy. In this chapter we focus on thermoset nanocomposites based on layered silicates and a lately emerging class of layered crystals known as layered double hydroxides G DHs). The use of polyhedral oligomeric silsesquioxanes and nanotubes nanocomposites is discussed in Chapter 10. The preparation of thermoset nanocomposites based on spherical nanosilica is also reported in the hterature. It is shown that while being heated in the nanocomposite, nanosilica, migrates to the surface of the material, due to the relatively low surface potential energy... 

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 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. 

Nanosilicas with a spherical shape of nonporous nanoparticles, controlled particle size distribution (PaSD), and specific surface area (Sbet) are appropriate nanosized materials to study the interfacial phenomena (without the strong distorting effects in nanopores) in different dispersion media. Nanosilicas are fully amorphous and can possess a larger 5bet value from 50 up to 500 mVg and a narrow PaSD (which becomes narrower at a greater Sbet value Her 1979, Ulrich 1984, Degussa 1997, Barthel et al. 1998a,b, Kammler and Pratsinis 2000, Kammler et al. 2004, Cabot Corporation 2011). 

Therefore, several series of nonporous and porous silicas unmodified and modified, differently hydrated, and placed in different dispersion media (air, nonpolar, weakly, or strongly polar) are analyzed here to elucidate their influence on the structure and properties of interfacial water. These investigations start from initial nanosilicas consisting with amorphous nonporous spherical primary particles forming secondary structures (aggregates and agglomerates). 

Nanosilica is composed of primary nanoparticles of a spherical shape, which form aggregates (Figure 1.29a) characterized by the textural porosity (Figure 1.58). 

FIGURE 1.188 (a) Nitrogen adsorption-desorption isotherms, and (b) primary partiele size distributions for siliea initial and MCA-treated wetted powder for 1 and 6 h caleulated using the adsorption data with the model of voids between spherical particles and the SCR procedure. (Adapted from J. Colloid Interface Sci., 355, Gun ko, V.M., Voronin, E.F., Nosach, L.V. et al.. Structural, textural and adsorption characteristics of nanosilica mechanochemically activated in different media, 300-311,2011e. Copyright 2011, with permission from Elsevier.)... 

FIGURE 1.254 Pore size distributions of unmodified and modified nanosilica A-380 (Table 1. 3) calculated on the basis of the nitrogen adsorption/desorption isotherms using DFT method with the model of pores as voids between spherical particles and NMR cryoporometry with IGT equation. (Adapted from/ Colloid Interface ScL, 308, Gun ko, V.M., Turov, V.V., Zarko, V.I. et al., Comparative characterization of polymethylsiloxane hydrogel and silylated fumed silica and silica gel, 142-156,2007h. Copyright 2007, with permission from Elsevier.)... 

FIGURE 6.19 The size distributions of pores filled by unfrozen water for (a) aqueous suspension of A-300 and the PSD calculated on the basis of the nitrogen adsorption/desorption isotherm (with the model of voids between spherical particles) (b) 0.15 mol NaCl or HPF solution at 1.25 and 2.5 wt% and (e) HPF/A-300 at different concentrations of protein and siliea. (Adapted with kind permission from Springer Seience+Business Media Cent. Eiir. J. Chem., Interaction of fibrinogen with nanosilica, 5, 2007, 32-54, Rugal, A.A., Gun ko, V.M., Barvinchenko, V.N., Turov, W., Semeshkina, T.V., and Zarko, V.I.)... 

Chapter 4 investigates the rheological and the dynamic mechanical properties of rubber nanocomposites filled with spherical nanoparticles, like POSS, titanium dioxide, and nanosilica. Here also the crucial parameter of interfacial interaction in nanocomposite systems under dynamic-mechanical conditions is discussed. After discussing about filled mono-matrix medium in the first three chapters, the next chapter gives information about the nonlinear viscoelastic behavior of rubber-rubber blend composites and nanocomposites with fillers of different particle size. Here in Chap. 5 we can observe a wide discussion about the influence of filler geometry, distribution, size, and filler loading on the dynamic viscoelastic behavior. These specific surface area and the surface structural features of the fillers influence the Payne effect as well. The authors explain the addition of spherical or near-spherical filler particles always increase the level of both the linear and the nonlinear viscoelastic properties whereas the addition of high-aspect-ratio, fiberlike fillers increase the elasticity as well as the viscosity. 

Later, Goren et al. (2010) eonducted a more systanatic study on the size effect using nanoparticles with the same base geometrical shape (spherical). They prepared PMMA silica nanocomposite foams using two nanosilica of different sizes... 

Several studies have also shown an improvement of the mechanical properties of rigid PU foams by adding small amounts of spherical-like nanosilica (Fan and Xiao-Qing, 2009 Wang et al., 2004 Xie and Wang, 2005). Particularly, Nikje and Tehran (2011) have incorporated two different types of silane-based surface-modified... 

The incorporation into PU foams of different types and concentrations of nanosized functional particles, both platelet-like such as nanoclays or graphene, fibrous-like such as carbon nanotubes and nanofibers, or even spherical-like such as nanosilica, has been shown to have a significant effect in the structure and physical properties of the resulting materials, considerably expanding the already wide range of possible applications of these lightweight materials. 

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