Surface chemistry particle characteristics

Fillers generally represent one of the major components by weight in an adhesive formulation. However, their concentration is quite often limited by viscosity constraints, cost, and negative effects on certain properties. The degree of improvement provided by a filler in an epoxy formulation will heavily depend on the type of filler and its properties (particle size, shape, size distribution, and concentration), surface chemistry, dispersion characteristics, dryness, and compatibility with the other components in the formulation. Table 9.3 summarizes the properties of selected fillers. 

The overall value of a filler is a complex fimction of intrinsic material characteristics, such as average particle size, particle shape, intrinsic strength, and chemical composition of process-dependent factors, such as particle-size distribution, surface chemistry, particle agglomeration, and bulk density and of cost. Abrasion and hardness properties are also important for their impact on the wear and maintenance of processing and molding equipment. 

The properties of fillers which induence a given end use are many. The overall value of a filler is a complex function of intrinsic material characteristics, eg, tme density, melting point, crystal habit, and chemical composition and of process-dependent factors, eg, particle-si2e distribution, surface chemistry, purity, and bulk density. Fillers impart performance or economic value to the compositions of which they are part. These values, often called functional properties, vary according to the nature of the appHcation. A quantification of the functional properties per unit cost in many cases provides a vaUd criterion for filler comparison and selection. The following are summaries of key filler properties and values. 

A general issue is that these nanocarbons are often only discussed in terms of a class of materials based on their shape (CNT, etc.). However, the growing understanding of these materials [16,33], of their controlled synthesis [34], and of the interfacial phenomena during interaction between nanocarbons and semiconductor particles [1,6,8,23,35] has clearly indicated that in addition to the relevant role given from the possibility to tune nanoarchitecture (and related influence on mass and charge transport, as well as on microenvironment [36]) the specific nanocarbon characteristics, surface chemistry and presence of defect sites determine the properties. 

General stmcture (fibrous or beaded form), particle size and variation, pore structures and dimensions, surface chemistry (hydrophilic or hydrophobic), swelling characteristics of matrix are important factors which effect chromatographic resolution [11,18]. Porosity of ion exchange... 

The three parameters, mean primary particle size (or specific surface area), structure (or aggregate size), and surface chemistry (e.g. surface oxides), largely determine the application characteristics of carbon blacks. A summary of how these parameters affect color and performance appears in Table 31. 

Zeolite surface chemistry resembles that of smectite clays. In contrast to clays, however, natural zeolites can occur as millimeter- or greater-sized particles and are free of shrink-swell behavior. As a result, zeolites exhibit superior hydraulic characteristics and are suitable for use in filtration systems (Breck 1974) and as permeable barriers to dissolved chemical migration. Internal and external surface areas up to 800 m2 g have been measured. Total cation exchange capacities in natural zeolites vary from 250 to 3000 meq kg 1 (Ming and Mumpton 1989). External cation exchange capacities have been determined for a few natural zeolites and typically range from 10 to 50 percent of the total cation exchange capacity (Bowman et al. 1995). 

The temperature dependence of the Payne effect has been studied by Payne and other authors [28, 32, 47]. With increasing temperature an Arrhe-nius-like drop of the moduli is found if the deformation amplitude is kept constant. Beside this effect, the impact of filler surface characteristics in the non-linear dynamic properties of filler reinforced rubbers has been discussed in a review of Wang [47], where basic theoretical interpretations and modeling is presented. The Payne effect has also been investigated in composites containing polymeric model fillers, like microgels of different particle size and surface chemistry, which could provide some more insight into the fundamental mechanisms of rubber reinforcement by colloidal fillers [48, 49]. 

Since the pioneering work of Knox et al. on CEC [9,10], porous silica particles have been used as the column packing material in the majority of research studies and applications. Porous silica has a number of characteristics that make it suitable for use in CEC. These are a large surface area, a high surface potential at moderate pH values, which allows the generation of a high EOF, and the commercial availability of materials with various surface chemistries. However, other support materials, such as polymeric phases [11] and alternative inorganic base materials [12], are also applicable in CEC. 

Particle characteristics Size, size distribution, shape, mechanical properties, surface chemistry, dispersion stability, concentration, agglomeration, and oversize particle count... 

The content of amorphous phase and the small size of spherulites lead to an improvement of the fracture toughness of Polypropylene [16]. In presence of mineral filler, the particle surface chemistry can induce some specific microstructural characteristics of the PP matrix parameters such as degree of crystallisation, spherulite size, and p phase content (a/p ratio) [16]. 

With CaC03, the spherulite size is significantly reduced (Ds = 10-15 pm) and the particle surface chemistry induces some specific microstructural characteristics of the PP matrix small size surface treated CaC03 particles promote formation of the p phase. Without surface treatment, CaC03 has a nucleating effect the degree of crystallisation is increased by about 20%(X(. = 65%). 

Carbon black finds its way into many products inks, paints, paper, fertilizer, plastics, and explosives to name a few. By far the major use, however, is in automotive tires which consume 65% of the total production. The present day tire contains roughly 1 pound of carbon black for each 2 pounds of rubber and provides both the bounce and wear characteristics desired by the user. The properties carbon black imparts to rubber compounds are so critical that there are currently more than 20 classified grades of oil blacks. Most distinctions between grades are mainly a function of particle size and structure, although surface chemistry is sometimes a factor for specialty uses. The more important grade designations are illustrated in Table I. Each of those listed are also subdivided according to their structure levels. 

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