Fullerene - polymer complexes: fractal crossover in solutions

Poly(vinylpyrrolidone)(PVP)-tetraphenylporphyrin(TPP)-C₆₀-complexes in heavy water at concentration C_P=1 wt.% have been studied at 293 K. Starting from PVP+TPP-complex and doping it with C₆₀ up to C~6 wt.%, we recognised complexes' structural evolution. We observed the changes from mass fractals with dimension D_M~2.3 at C=0 wt.% to surface fractals, having dimension D_S ~2.8 at C~2 wt.%. Then the system returns to mass fractals, D_M(C)~2.9-2.8 at C~5-6 wt.%. These structural peculiarities we explain as a result of cross linking action of fullerene, forming a microgel above a critical concentration C*~1 wt.%. Meanwhile, the network of over-doped complex (C~5 wt.%) is degraded, indicating a strong influence of fullerene on the water structure.