Delivery of fullerene-containing complexes via microgel swelling and shear-induced release

Abstract

The absorption and release of poly(vinylpyrrolidone)-fullerene C 60 complexes (PVP/C 60) from a model microgel is studied. A dry microgel based on a chemically cross-linked sodium polyacrylate was swollen in the aqueous solutions of complexes which were afterwards released under shear stress. First, gel swelling degree in static conditions in the excess of PVP/C 60 solutions was studied: the degree of swelling decreases with the increase in PVP/C 60 concentration. While pure PVP is homogeneously distributed between the gel and the surrounding solution, a slight concentration of complexes outside the gel was recorded. It was attributed to PVP/C 60 hydrophobicity leading to the decrease in the thermodynamic quality of fullerene-containing solution being gel solvent. The release of PVP/C 60 solutions induced by shear was studied with counter-rotating rheo-optical technique and compared with PVP solution release under the same conditions. The amount of solution released depends on polymer concentration and shear strain. Contrary to pure PVP solutions in which rate of release decreases with the increase in polymer concentration, PVP/C 60 complexes are released faster when fullerene concentration inside the gel is higher.