Adsorption of oligomers with different functional groups from solutions in xylene on carbon black samples

The adsorption of special additives containing different functional groups: acidic (No. 1), basic (No. 2) and quaternary ammonium (No. 3) from solutions in xylene was studied on carbon black samples used in the domestic coatings industry.

According to the size of the specific surface S, the studied samples are divided into mesoporous (S < 400 m²/g) and microporous (S > 400 m²/g). The shape of the adsorption isotherms of the studied mesoporous carbon black belongs to type IV and V according to the classification of Brunauer, Emmet and Teller, and microporous to type I. For mesoporous carbon black, the adsorption value in the monolayer of the main additive No. 2 is greater than additives No. 1 and No. 3, the adsorption of which practically does not differ. The adsorption values of additives No. 1, No. 2 and No. 3 in a monolayer on the surface of these carbon black are 10 times less than on the surface of TiO₂. Thus, in the case of carbon black, adsorption is due only to dispersion interactions. The Аm areas occupied by the molecules of additive No. 2 in a dense monolayer on the surface of mesoporous carbon black are calculated.

The Аm values determined from the experimental isotherms significantly exceed the А_m value calculated theoretically, which is explained by the high degree of porosity of the studied carbon black and the inaccessibility of most pores to adsorbate molecules. Monolayer thicknesses for additive No. 2 and cylindrical pore radii were calculated for mesoporous carbon black. The maximum value of adsorption corresponds to the completion of polymolecular adsorption and filling of pores by the mechanism of capillary condensation.

In accordance with the Gurvich rule, the volume of pores available for the studied additives was determined for mesoporous carbon black. In the case of microporous samples, the adsorption value of additives is several times greater. However, the adsorption per surface unit is significantly less than the corresponding values for mesoporous carbon black with a low S value, which indicates the presence of a large number of small pores inaccessible to additive molecules. The convex shape of the isotherms for these carbon black samples is explained by the fact that the filling of micropores begins already in the region of low concentrations by volumetric filling without capillary condensation and the plateau on the isotherms corresponds to the completion of this process. The maximum value of adsorption is determined by the available volume of the porous space of the sorbent.

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