Wettability carbon blacks

Adsorption Properties. Due to their large specific surface areas, carbon blacks have a remarkable adsorption capacity for water, solvents, binders, and polymers, depending on their surface chemistry. Adsorption capacity increases with a higher specific surface area and porosity. Chemical and physical adsorption not only determine wettability and dispersibility to a great extent, but are also most important factors in the use of carbon blacks as fillers in rubber as well as in their use as pigments. Carbon blacks with high specific surface areas can adsorb up to 20 wt% of water when exposed to humid air. In some cases, the adsorption of stabilizers or accelerators can pose a problem in polymer systems. 

Oxidized carbon blacks may contain up to 15 wt% oxygen. They are strongly hydrophilic. Some of them form colloidal solutions spontaneously in water. In polar printing ink systems, lacquers, and coatings, a better wettability and dispersibility is achieved through surface oxidation [4.26], thus reducing binder consumption. 

Another important property is the structure (see Section 4.1) which characterizes the coalescence of primary particles into aggregates resembling chains or bunches of grapes. The dibutyl phthalate (DBP) absorption is commonly accepted as a measure for the carbon black structure. Due to absorption phenomena the DBP number increases with increasing specific surface area. Oil absorption (or, in general, the vehicle demand) is as well an indicator for the structure, but it also depends on the wettability of the black surface. Since linseed oil is a polar system, oil absorption declines as the concentration of surface oxides rises. 

Chemical heterogeneity of a surface is an important property affecting adhesion, adsorption, wettability, biocompatibility, printability and lubrication behavior of a surface. It seriously affects gas and liquid adsorption capacity of a substrate and also the extent of a catalysis reaction. As an example, the partial oxidation of carbon black surfaces has an important, influence on their adsorptive behavior. In a chemically heterogeneous catalyst, the composition and the chemical (valence) state of the surface atoms or molecules are very important, and such a catalyst may only have the power to catalyze a specific chemical reaction if the heterogeneity of its surface structure can be controlled and reproduced during the synthesis. Thus in many instances, it is necessary to determine the chemical... 

Oxidation of carbon surfaces also affects electric conductivity or wettability of electrodes. Horita and co-workers [170] reported the relationship between the pore structure and the surface properties of carbon blacks electrode modified by anodic oxidation. The polarization behavior of an oxygen electrode is much improved by the anodic oxidation, owing to adequate wettabili, and highly develop fine pores of the electrode. 

These columns (i.d. < 200 pm) are characterized by a high specific efficiency (number of theoretical plates per meter and per second). Cartoni and co-workers [44] described the technique for preparing glass and fused-silica capillary columns (100 pm i d ), which were precoated with a very thin layer of graphitized carbon black and then coated with polar liquid phases. The layer of carbon black increased the wettability of the capillary columns walls and a very uniform coating was obtained. Columns coated with Carbowax 20 M, 40 M and 600 M were prepared. Polar liquid phases were strongly retained on carbon black, and these column showed higher temperature stability. 

The procedure for preparation of these columns is not complicated. The columns were precoated with a graphitized carbon black Carbopack A (Sg - 12 m /g). The dynamically deposited carbon black increased the surface area and solid stationary phase wettability and consequently a very uniform coating was obtained [44]. Suspension of graphitized carbon black (GCB) was prepared with 50 mg GCB, 25 ml carbon tetrachloride, 25 ml dichloromethane and then exposed to an ultrasonic bath for about 30 min. Approximately 2 ml of this suspension were made to flow through the capillary four times at high speed (60 cm/s), reversing the flow direction each time and waiting for the solvent... 

The second way that the fillers can be characterized is by their interaction with the polymer matrix. The fillers can be adherent to the polymer matrix whether inherently or by special surface treatment. The fillers may absorb the polymer phase because of high surface area and inherent wettability. They can react chemically with the polymer material to form a chemical bond, again, both by inherent structure or by suitable surface treatment. The filler can be catalytic to the structure and, in addition to acting as a filler can cause crosslinking of the structure, notably in the case of carbon black. Finally, the filler can be inert and nonadherent to the polymer and remain as just a void filler. 

Studebaker ML, Snow CW. The influence of ultimate composition upon the wettability of carbon blacks. J Phys Chem 1955 59 973-6. 

There are four fundamental properties of carbon blacks which determine how these materials can be used with optimization. One Fineness and particle size distribution (Figure 2.39) influence blackness and tint. Two Structure within the carbon black particle and the aggregation of the particles (also called structure. Figure 2.39) influence dispersibility and electrical conductivity. Three Porosity and pore-size distributions influence viscosity and coverage requirements. Four The presence of surface functionality influences wettability, viscosity and electrical conductivity. In carbon black usage, it is their external surfaces, with oxygen functionality in some cases, which dominate their sorption properties, as distinct from the internal microporosity as found in activated carbon. Carbon blacks are supplied by manufacturers both as powders and as pellets. 

The surface oxide groups on carbon play a major role in its surface properties for example, the wettability in aqueous electrolytes, work function, and pH in water are strongly affected by the presence of surface groups on the carbonaceous material. Typically, the wettability of carbon blacks increases as the concentration of surface oxides increases [16]. The pH of an aqueous slurry of carbon decreases as the volatile or oxygen content of the carbon increases [17]. The work function of carbon blacks shows a minimum at a pH near 6 [18]. 

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