Isotherms of the specific surface excess and of the enthalpy of displacement (enthalpy of adsorption from solution) are reported for dilute solutions of n-docosane (n-C22H46) in heptane onto graphitized carbon black, for tempertures from 15 to 45 °C.
As already noted by previous authors long-chain n-alkanes are strongly preferentially adsorbed onto the graphite basal plane. The present work shows that the isotherms for such a system exhibit a positive initial curvature and a point of inflection before approaching a plateau corresponding to a complete adsorbed monolayer. This deviation from ideal Langmuir-type behaviour is attributed to strong lateral interactions between long-chain molecules adsorbed side-by-side on the flat graphite basal plane. There are indications for a phase separation in the adsorbed layer at the lower temperatures, involving the formation of close-packed ordered arrays of n-docosane molecules on the surface. — The experimental results can be accounted for quantitatively by the parallel layer model of adsorption from non-athermal solutions of chain molecules.
Carbon Black Adsorbed Layer Molar Enthalpy Chain Molecule Standard Molar Enthalpy
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