Adsorption of nitrogen, n-butane and neo-pentane on chloro-hydrocarbon polymers

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Abstract
Isotherms for adsorption of nitrogen at 78.3–92.4 K on powdered samples of polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC) and of n-butane and neo-pentane on PVDC at 256.2–294 K have been measured in the monolayer region. Effective cross-sectional areas of adsorbed n-butane and neo-pentane, calculated from B.E.T. plots and based on nitrogen-determined surface areas, are comparable with values obtained from the densities of the liquids. For θ < ca. 0.5, isosteric heats of adsorption of nitrogen on PVC correspond closely with those on PVDC. Isosteric heats for n-butane and neo-pentane show that PVDC has a low energy surface, and the heats for n-butane decrease significantly below the heat of liquefaction with increasing coverage. Lower heats of adsorption of n-butane, compared with neo-pentane, suggest that n-butane is adsorbed on PVDC in a perpendicular position rather than lying parallel with the surface. Nitrogen isotherms at 78 K on PVC of specific surface area 1.2 m2 g–1 show evidence of stepwise adsorption, and nitrogen adsorption at 78 K on γ-hexachlorocyclohexane gives a specific surface area of 0.7 m2 g–1 and a B.E.T. c value of 10.

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