Physical Meanings of Fractal Behaviors of Water in Aqueous and Biological Systems

Dynamics of Hydrogen Bonding Network (HBN) relating to macroscopic properties of hydrogen bonding liquids were observed as the largest relaxation process by dielectric spectroscopy measurements. In the cases of water and water rich mixtures including biological systems, a GHz frequency relaxation process appearing at around 20GHz with the relaxation time of 8.2ps is generally observed at 25°C. The GHz frequency process can be explained as a rate process of exchanges in HB and the rate becomes higher with increasing HB density. In the present work, we analyzed the GHz frequency process and clarified physical meanings of the fractal nature of water structures in various aqueous systems. Dynamic behaviors of HBN were characterized by a combination of the average relaxation time and the distribution of the relaxation time. The fractal analysis offered an available approach to both solution and dispersion systems with characterization of the aggregation or dispersion state of water molecules. In the case of polymer-water mixtures, the HBN and polymer networks well penetrate each other. However, the HBN were segmented and isolated more by dispersed and aggregated particles in the case of dispersion systems. These HBN fragments were dominantly evaluated by smaller values of the fractal dimension obtained from the fractal analysis, but it is also related with other two parameters. The fractal analysis is now one of the most effective tools to understand molecular mechanism of HBN in aqueous complex materials including biological systems.