Spatial and temporal scale of cooperative motions in supercooled liquids

利用超声光谱、介电光谱和拉曼光谱技术对过冷液体中协同运动的时空尺度进行了研究。结果如下：(1)测定了丙二醇（PG）、1,2,6 -己三醇和四（乙二醇）-己三醇二元混合物在5 MHz ~ 10 GHz频率范围内的超声光谱与温度的关系。对于PG、己三醇和peg -己三醇二元混合物，观察到由于结构弛豫引起的速度色散，并在测量频率和温度范围内得到光滑的主曲线。结构松弛过程的平均松弛时间与线性粘弹性理论估计的松弛时间基本一致。(2)在248 ~ 298 K的微波区测量了聚乙二醇的复介电谱。简化后的复介电常数可以在主曲线上叠加更多的城市。在降低介电常数的Cole-Cole图上观察到的高频侧拐点表明在皮秒区域存在快速的协同过程。(3)在组成比为1:1的聚乙二醇、己三醇和聚乙二醇-己三醇二元混合物的低频光谱中观察到一个宽峰，称为玻色子峰。扩展无序诱导散射模型再现了玻色子峰的线形，并估计了结构相关长度。(4)聚乙二醇在750 ~ 950 cm^<-1>范围内的拉曼光谱表明，液态的构象与温度有关，随着温度的降低，构象与结晶的构象接近，直至玻璃化转变温度为7_g。(5)测定了二糖、海藻糖和麦芽糖的浓水溶液在微波波段的复介电谱。海藻糖的松弛时间大于麦芽糖，类似于超声松弛的情况。两种溶液的活化能均小于水的活化能。少

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