Involvement of fractal geometry on solute permeation through porous poly (2-hydroxyethyl methacrylate) membranes

Fractal geometry was applied to quantify the complexity of an internal structure of porous membranes prepared with poly(2-hydroxyethyl methacrylate) (pHEMA). The porous pHEMA membranes were synthesized by means of free-radical solution polymerization. Boundary lines of the porous structures in the pHEMA membrane were taken by a scanning electron microscope as image data, and these images were fed into a computer to estimate the fractal dimension. The boundary images of porous pHEMA membranes were observed to be a typical fractal and their complexity was quantified as a non-integral fractal dimension. The permeation of fluorescein isothiocyanate-labeled dextran, molecular weight 4400 (FD-4) as a model penetrant through the porous pHEMA membrane was determined using water-jacket type two-chamber diffusion cells. A fairly good negative relationship between the permeability coefficient of FD-4 and the fractal dimension was observed, suggesting the usefulness of the fractal dimension as a novel means for evaluating solute permeation through the porous membranes.