Geometrical characterization of polymeric matrices by means of dielectric spectroscopy measurements

The dielectric behavior of water-imbibed highly porous polymeric matrices with randomly oriented interconnected pores has been investigated by means of dielectric relaxation spectroscopy in the frequency range from 1 kHz to 2 GHz. The confinement of an aqueous phase into mesoscopic regions (from 10 nm to 100 mm in size) inside the porous material results in the appearance of a new relaxation process due to the interfacial orientational polarization of the aqueous phase at the polymer interface. Within the framework of the effective medium theory approximation, based on the local porosity theory, the analysis of the dielectric spectra allows us to obtain the geometrical characterization of the system, as far as the pore distribution and the degree of pore inter-connectivity are concerned. We have investigated four different porous polymeric media prepared by different polymeric materials, with different size and shape of the pores and different degrees of interconnection. For each of them, we have derived two characteristic functions, the local porosity distribution mu(phi) and the local percolation probability lambda(phi), which completely characterize their geometrical properties, as far as the porosity is concerned. In particular, the knowledge of the percolation probability lambda(phi) represents a key parameter in the optimization of polymeric matrices for applications such as tissue engineering in order to meet the appropriate requirement for cell attachment, cell proliferation, tissue regeneration and nutrient flow and in the field chromatography, solid phase synthesis and scavenging.