Microcalorimetric studies of the adsorption of N-ethylpyrrolidone, oligomeric and polymeric vinylpyrrolidone from CHCl₃ on silica

Abstract

Adsorption enthalpies of N-ethylpyrrolidone, oligomeric and polymeric vinylpyrrolidone from CHCl₃ solution on silica interfaces (Aerosil 200) have been measured at 25 °C by microcalorimetry. The dependence on surface coverage has been examined using measured adsorption isotherms. Binding enthalpies are calculated with fractions of adhered segments obtained by IR spectrometry and wetting enthalpies received from calorimetry. Fractions of adhered segments are derived from the adsorption enthalpies assuming equal binding enthalpies of monomers and polymer segments and considering desorption enthalpies of the solvent depending on the surface area of the polymer segments. The resulting enthalpies are compared with literature values from other solvents and the incongruity of the fraction of adhered segments obtained by IR, ESR, NMR and microcalorimetry is explained.