Graphon = graphite

This paper describes a study of the dispersibility of Graphon (graphitized Spheron 6) in aqueous solutions of sodium dodecyl sulfate (SDS) an dodecyl trimethylammonium bromide (DTAB), and its relation to the adsorption behavior of the surfactants at the solid/liquid interface, with a view to determine the controlling process in the dispersibility of these systems. 

Figure Ic differs markedly from those obtained for the immersion of polar solids in water initially the heat values are small but increase with increasing amounts of preadsorbed water. Thus far, only one such curve has been reported in the literature for the system Graphon-water 90). Graphon is a graphitized carbon black which has an essentially homogeneous, homopolar surface 21). Nevertheless, a small fraction of heterogeneous sites is responsible for the limited adsorption of water on the surface of this solid. Similar curves can be expected for other hydrophobic solids.

Heats of immersion provide a new tool for rating the wetting ability of surfactants from aqueous solution. If a high-area graphite, Graphon, or carbon black is used, the increased heat effect obtained with the surfactant solution over that obtained with water allows the wetting tendency of the surfactant to be rated (71). Typical heats of immersion in surfactant solutions are listed in Table IX. 

Pierce and Smith (56) have observed a Type III isotherm for water vapor on a highly graphitized carbon black (graphon, 80 square meters per gram) at 28.9° C. They suggest that water vapor adsorption occurs only on the most active sites and that the entire surface is probably never covered. 

The system described in this investigation is polystyrene-14C adsorbed on Graphon carbon black (graphitized Spheron 6) from six solvents comprising a wide spectrum from good to poor solvent power. Well-characterized materials were selected to elucidate the conformation of polymer molecules at the solid/liquid interface. So far two models have been postulated to describe the conformation of the adsorbed polymer molecules at the solid/liquid interface (9, 13, 14, 18, 19, 21, 27). In the first model the polymer assumes a loop or coil structure in which only a fraction of the polymer segments are attached directly at the interface, and in the second model the polymer forms a relatively flat and compressed interfacial layer with many segments attached to the solid substrate. 

Graphon black, kindly furnished by the Cabot Corporation, was the adsorbent and its physical properties are listed in Table I. The term Graphon refers to Spheron 6 which had been heated to 2,700°-3,200°C. This graphitized nonporous carbon black is a unique form of carbon with uniform surface and high surface area. The Graphon samples were dried for 12 hrs. at 140°C. and stored in vacuo before use in the adsorption experiments. 

Similar data (not shown (2j6)) for the graphitized black, Graphon, exhibits little evidence for significant interaction with either white reference solid. 

For the adsorption of hexane on graphite we may use the experimental results of Isirikyan and Kiselev [18], who found that on graphi-tized carbon black (Graphon) n-hexane occupies 54 sq. A. per molecule and has a heat of adsorption (with liquid hexane as standard state) of 5.0 kcal. per mole. The value of y for graphite which gives a heat of adsorption of 5.0 kcal. per mole is found by Equation 8 to be 108 dynes per cm. 

Figure 10.12. Correlation between bound rubber and specific surface area. The data are for 50 parts of black per 100 parts of SBR 1500. Graphon, a graphitized carbon, does not follow the correlation. (Kraus, 1965c.)...

The carbon substrate was a graphitized carbon black, Graphon [Cabot U.K.], with a specific surface area of 80 m /g. The y-alumina sample was obtained from Prest [Grenoble France] and had a specific surface area estimated at 200m /g. However this sample consisted of aggregates of approximately 1 pm in size which were made up of smaller particles of the order of 9nm diameter. The area available for polymer adsorption was therefore considerably less than the nominal nitrogen BET area quoted above. The tetrachloromethane and cyclohexane were obtained from the Aldrich Co. [U.K.] and were spectroscopic grade. 

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