Spatial and temporal scale of cooperative motions in supercooled liquids

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The Spatial and temporal scale for cooperative motions in supercooled liquids were investigated using ultrasonic spectroscopy, dielectric spectroscopy and Raman spectroscopy technique in the wide temperature range. The results are listed as follows.(1) The ultrasonic spectra in the frequency range from 5 MHz to 10 GHz for propylene glycol (PG) , 1, 2, 6-hexanetriol and tetra (ethylene glycol) (PEG) -hexanetriol binary mixtures have been measured as a function of temperature. For PG, hexanetriol and PEG-hexanetriol binary mixtures, the velocity dispersions attributed to the structural relaxation are observed and smooth master curves are obtained in the measured frequency and temperature ranges. Averaged relaxation times of the structural relaxation processes are in reasonable agreements with those estimated by the linear viscoelastic theory.(2) Complex dielectric spectra of PEG were measured in the microwave region in the temperature range from 248 to 298 K.The reduced complex permittiv … More ity could be superimposed on a master curve. The observed point of inflection in the high frequency side at the Cole-Cole plot of reduced permittvity suggest that there are fast cooperative process in the picosecond region.(3) A broad peak known as a boson peak is observed in the low-frequency spectra in PEG, hexanetriol and PEG-hexanetriol binany mixture with composition ratio of 1 : 1. The extended disorder-induced scattering model reproduces the line shape of the boson peak and structural correlation length is estimated. The structural correlation length are order of 1 nm and the fluctuation of times of are around 10 ps.(4) Raman spectra of PEG from 750 to 950 cm^<-1> indicate that the conformation in the liquid state depends on temperature and may approach to that in the crystalline state with decreasing temperature down to the glass transition temperature 7_g.(5) Complex dielectric spectra of concentrated aqueous solution of the disaccharide, trehalose and maltose, were measured in the microwave region. The relaxation time of trehalose is larger than that of maltose similar to the case of ultrasonic relaxation. The activation energies for both solution is smaller than that of water. Less