Chain-like agglomerate

FIGURE 8.8 Photomicrographs of chain-like agglomerates (a) chain-like agglomerates of hematite particles in the presence of the geomagnetic field (b) in the absence of the field. 

On surface it is very simple model but effective concentration of filler includes observation that some layer of polymer is bound to the surface of filler and the mechanisms of this bonding is mathematically expressed by effectiveness factor. The recent model assumes that filler particles are spheres which might be connected to form chain-like agglomerates. Each particle is surface coated with matrix polymer. The elastomeric layer is considered immobilized. The effective filler volume is higher than filler volume fraction by the amount of adsorbed polymer. The effectiveness factors is given by equation ... 

Figure 7-3. (a) Transmission electron micrograph of spherical agglomerations of emulsion-synthesized alumina particles (Siladitya et al, 1999). (b) Transmission electron micrograph of chain-like agglomerations of emulsion-synthesized alumina particles (Siladitya et al, 1999). Permission for reproduction obtained from Kluwer Academic Publishers, U.S.A. Photograph kindly supplied by Dr. M. Chatterjee, Central Glass and Ceramic Research Institute, Kolkata, India. 

Carbon black formed chain-like stmcture within the nonpolar polypropylene matrix in the form of agglomerates rather than as individual particles because of the poor wetting of carbon black. The carbon black distribution in PP was relatively... 

As with carbon blacks, silica fillers are characterized on the basis of primary particle size and specific area. The smallest observable single filler particles (primary) have diameters of about 15 nm. The surface forces of the primary filler particles are so high that thousands of them agglomerate to form extremely robust secondary particles that cannot be broken apart. These secondary particles further agglomerate to form chain-like tertiary structures, many of which can be more or less degraded by shear forces. Determination of surface areas is done using the BET nitrogen absorption method. 

Macromolecules have also been specifically designed and synthesized for use as emulsifiers for lipophilic materials and as stabilizers in the colloidal dispersion of lipophilic, hydrocarbon polymers in C02. We have demonstrated the amphiphilicity of fluorinated acrylate homopolymers, such as PFOA, which contain a lipophilic, acrylate like backbone and C02-philic, fluorinated side chains (see Fig. 3) [103]. It has been demonstrated that a homopolymer which physically adsorbs to the surface of a polymer colloid prevents agglomeration by the presence of loops and tails (see Fig. 4) [113]. The synthesis of this type of... 

The gap between the predictions and experimental results arises from imperfect dispersion of carbon nanotubes and poor load transfer from the matrix to the nanotubes. Even modest nanotube agglomeration impacts the diameter and length distributions of the nanofillers and overall is likely to decrease the aspect ratio. In addition, nanotube agglomeration reduces the modulus of the nanofillers relative to that of isolated nanotubes because there are only weak dispersive forces between the nanotubes. Schadler et al. (71) and Ajayan et al. (72) concluded from Raman spectra that slippage occurs between the shells of MWNTs and within SWNT ropes and may limit stress transfer in nanotube/polymer composites. Thus, good dispersion of CNTs and strong interfacial interactions between CNTs and PU chains contribute to the dramatic improvement of the mechanical properties of the... 

The service performance of rubber products can be improved by the addition of fine particle size carbon blacks or silicas. The most important effects are improvements in wear resistance of tire treads and in sidewall resistance to tearing and fatigue cracking. This reinforcement varies with the particle size, surface nature, state of agglomeration and amount of the reinforcing agent and the nature of the elastomer. Carbon blacks normally are effective only with hydrocarbon rubbers. It seems likely that the reinforcement phenomenon relies on the physical adsorption of polymer chains on the solid surface and the ability of the elastomer molecules to slip over the filler surface without actual desorption or creation of voids. 

In this work the primary pore structure of the beads was varied according to a hydrothermal treatment procedure (step 2). In order to control the secondary pore structure of the agglomerates, the primary particle size has to be adjusted. This can be carried out varying synthesis parameters (step 1) like the concentration of ammonia and water [4], the chain length of the alcohol [5] and the synthesis temperature [6],... 

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