Graphon carbon black

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. 

Mogul carbon black of Mogul carbon black of Mogul-A carbon black Mogul-A carbon black ELF-O carbon black of ELF-O carbon black of Spheron-6 carbon black Spheron-6 carbon black Graphon carbon black of Graphon carbon black... 

Figure 40 Low-resolution Raman spectrum of graphon (exciting line, 514.5 nm Ar", 240 mW, rotating cell, 3000 rpm) [117]. (Reproduced from Carbon 22, Mernagh, T. R, et al., Raman spectra of graphon carbon black, pp. 39-42. Copyright 1984, with permission from Elsevier Science.)...

Fig. XVn-21. (a) Differential heat of adsorption of N2 on Graphon, except for Oand , which were determined calorimetrically. (From Ref. 89.) (b) Differential heat of adsorption of N2 on carbon black (Spheron 6) at 78.5 K (From Ref. 124).

Fig. 2.25 The differential heat of adsorption of argon on carbon blacks at 78 K, before and after graphitizalion.. Spheron O, Graphon. , and El denote molar heat of sublimation and of evaporation respectively.

Fig. 4.2 Equilibrium adsorption of sodium n-dodecyl sulfate on carbon black, Ti02, and Graphon at room temperature [41].

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 adsorption isotherms for carbon black and graphitised carbon black (graphon) are completely different. For graphitised carbon black a step-like adsorption isotherm is... 

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. 

Several examples may be quoted from the literature to illustrate the adsorption of surfactant ions onto soHd surfaces. For a model hydrophobic surface, carbon black has been chosen [22, 23], and Figure 5.5 shows the typical results for the adsorption of sodium dodecyl sulphate (SDS) onto two carbon black surfaces, namely Spheron 6 (untreated) and Graphon (graphitised), which also describes the effect of surface treatment. 

The adsorption of ionic surfactants onto hydrophobic polar surfaces resembles that for carbon black [24,25]. For example, Saleeb and Kitchener [24] found a similar limiting area for cetyltrimethyl ammonium bromide on Graphon and polystyrene ( 0.4nm ). As with carbon black, the area per molecule depended on the nature and amount of the added electrolyte. This can be accounted for in terms of the reduction in head group repulsion and/or counterion binging. 

However, Graphon proved to be almost totally benign in the titration and EM experiments, while BPL was very active in both experiments though the equality of the values for Graphon and BPL would indicate similar behavior for the two blacks if the physical and chemical processes involved were governed solely by an electronic structure that was well characterized by . Clearly, details of the electronic structures of the carbon black are important to understanding their interactions with other materials. 

The inactivity of Graphon in the contacts with the white solids despite the near equivalence of its work function with that of BPL demonstrates an absence of coupling of the delocalized tr electron system of Graphon with the localized Bronsted and Lewis sites of the white solids. It is to be noted that electron transfer between the tt electron systems of different carbon blacks occurs quite readily. The oxide structures of carbon blacks are seen to play a fundamental role in this viewpoint at the microscopic level akin, for example, to the critical importance of the molecular structures of the adsorbates in chemisorption from the gas phase onto metals (41, 42) and metal oxides(43). 

It is worth noting that the model for the carbon black surface deduced from these observations possesses a limited predictive capability for other materials systems than those studied herein. The current viewpoint that polymer interactions may be discussed in terms of Lewis acidity and basicity associated with particular molecular groups comprising the polymer(44-46) coincides with the present description of the origin of carbon black activity. Specifically BPL, which contains localized Lewis acid sites, can be expected to interact readily with polymer sites that are capable of acting as a Lewis base towards the carbon sites. On the other hand Graphon, which lacks these localized Lewis acid sites, is predicted to interact weakly with the same polymer sites. Contact charge injection experiments (3 3) provide a particularly sensitive probe of the carbon-polymer interaction and may supply the best means to test such model predictions. 

Adsorption of sodium bis(2-ethy hexyl)sulfosuccinate from benzene solution onto carbon blacks follows the Langmuir equation and depends on the amount of oxygen on the surface. No adsorption onto heat-treated hydrophobic carbon (Graphon) could be detected (Abram, 1962). 

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. 

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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