Pyrrolidinium salts based ionic liquids are known to be good ionic conductors even in solid-state around room temperature, which is attributed to the highly disordered plastic crystalline phase. Moreover, these salts are characterized by multiple phase transitions which include plastic, structural glass, and glassy crystal phases with varying levels of molecular disorder. Temperature-dependent Brillouin light scattering is used to investigate the phase transitions in a series of alkylmethylpyrrolidinium Bis(trifluoromethanesulfonyl) imides (P_1nTFSI, n = 1,2,4). Brillouin spectral features such as the number of acoustic modes, their shape, and linewidths provide the picture of different disordered phases resultant of dynamics at the microscopic scale. The longitudinal and transverse acoustic velocities in different phases are determined from the corresponding acoustic mode frequencies (Brillouin shift). Extremely low acoustic velocities in the solid phase of P₁₁TFSI and P₁₂TFSI are a consequence of a high degree of disorder and plasticity present in these systems. Anomalous temperature-dependent behavior of linewidths and asymmetric (Fano) line shape of acoustic modes observed in certain phases of P_1nTFSI could be due to the strong coupling between the Brillouin central peak and the acoustic phonons. The present results establish that the Brillouin light scattering technique can be efficiently used to understand the complex phase behavior, microscopic structure, and dynamics of ionic liquids.

已知基于吡咯烷鎓盐的离子液体即使在室温下处于固态时也是良好的离子导体，这归因于高度无序的塑性结晶相。而且，这些盐的特征在于多个相变，包括具有不同水平的分子无序的塑料相，结构玻璃相和玻璃态晶相。与温度有关的布里渊光散射用于研究一系列烷基甲基吡咯烷鎓双（三氟甲烷磺酰基）酰亚胺（P _1n TFSI，n = 1,2,4）。布里渊频谱特征（例如声学模式的数量，它们的形状和线宽）提供了微观尺度上动力学产生的不同无序相的图像。根据相应的声模频率（布里渊频移）确定不同相位的纵向和横向声速。P ₁₁ TFSI和P ₁₂ TFSI固相中的极低声速是这些系统中存在高度杂乱和可塑性的结果。在P _1n的某些相位中观察到的线宽异常与温度相关的行为以及声模的不对称（Fano）线形TFSI可能是由于布里渊中央峰和声子之间的强耦合。目前的结果表明，布里渊光散射技术可以有效地用于理解复杂的相行为，微观结构和离子液体的动力学。