Abstract
Adsorption of polyvinylpyrrolidone (PVP) from aqueous solution on chloramphenicol was measured. The adsorption data fitted the Langmuir isotherm. The adsorption capacity (χ∞) slightly increased with molecular weight (M) according to the relationship χ∞=KMα, where α was 0.11. Assuming that PVP molecules lie flat on the surface of chloramphenicol particles, χ∞ in all cases corresponds to 2-3 molecular layers. The amount of PVP adsorbed increased with temperature. This apparent decrease in free energy is associated with a large positive entropy contribution due to the liberation of water molecules from the polymer and the aqueous-solid interface. The protective action of PVP on chloramphenicol suspension was also determined by the sedimentation volume (SV) method. The SV decreased with molecular weight of PVP and increased with rising temperature. The stabilizing effect of PVP on the chloramphenicol suspension can be plausibly explained on the basis of the thermodynamic properties of aqueous solution of PVP and the configuration of PVP adsorbed.
