Viscosity Measurements of the Freeze Concentration Solution Confined in the Space Surrounded by Ice Crystals

Abstract

In this chapter, the viscosities of the FCS in frozen glycerol/water solutions are evaluated by two spectrometric methods of different principles: (1) the reaction rate of the diffusion-controlled emission quenching and (2) fluorescence correlation (FCor) spectroscopy (Inagawa et al. in J Phys Chem C 121:12321–12328, 2017 [1]). Thermodynamics indicates that the concentration of glycerol in the FCS is constant at a constant temperature, regardless of the glycerol concentration in the original solution before freezing (\\(c_{\\text{gly}}^{\\text{ini}}\\)). However, the viscosity of the FCS measured at a given temperature increases with decreasing \\(c_{\\text{gly}}^{\\text{ini}}\\) and becomes more pronounced with decreasing measurement temperature. Further, the viscosity of the FCS in a rapidly frozen solution is higher than that observed in a slowly frozen solution. These results suggest that the viscosity of the FCS depends on the size of the space in which the FCS is confined and increases in smaller spaces. This result agrees well with several reports of anomalous phenomena in a microspace confined in ice. These phenomena originate from the fluctuation of the ice/FCS interface, which is macroscopically stable but microscopically dynamic and undergoes continuous freezing and thawing. Thus, the FCS near the interface displays ice-like physicochemical properties and structures, thereby affording higher viscosity than the corresponding bulk solution.