Microheterogenities and Crossover from Ising to Mean Field Criticality in Solutions of Ionic Liquids

本文将通过静态和动态光散射在介观尺度上研究离子液体溶液的结构和动力学。在临界解点附近，临界波动主导散射，但其他平衡和非平衡不均匀性也有贡献，并将应用新技术进行分析。对应态分析表明，在非极性溶剂中，液-液相变主要由库仑相互作用决定，而随着极性的增加，疏溶剂相互作用占主导地位。结果表明，离子溶液的液-液相变总是属于伊辛普适类。虽然临界点的性质是不变的，当库仑力或疏溶剂的相互作用驱动相变，它是不清楚的，如果这是真的，也为交叉从伊辛到定期的行为。当库仑力驱动相变时，一些理论预测一个大的，另一些理论预测一个小的非经典区域与三临界点交叉。然而，非临界介观结构可能被错误地解释为交叉。为了澄清这种情况，我们将研究离子液体在不同介电常数的溶剂（包括烃类、醇类和水）中的溶液的光散射。能够形成液晶的离子液体溶液将被研究，因为在这样的系统中，很可能会交叉到三临界点。

Structure and dynamics of solutions of Ionic Liquids will be investigated on a mesoscopic scale by static and dynamic light scattering. Near a critical solution point the critical fluctuations dominate the scattering, but other equilibrium and non-equilibrium inhomogeneities contribute and will be analyzed applying new techniques. Corresponding state analysis indicates that in non-polar solvents the liquid-liquid phase transition is determined by the Coulomb interactions, while with increasing polarity solvophobic interactions become dominant. It was shown that the liquid-liquid phase transitions of ionic solutions always belong to the Ising universality class. While the nature of the critical point is unchanged, when Coulomb forces or solvophobic interactions drive the phase transition, it is not clear if this is true also for the crossover from Ising to regular behaviour. Some theories predict a large, others a small non-classical region with crossover to a tricritical point, when Coulomb forces drive the phase transition. However, non-critical mesoscopic structures may erroneously be interpreted as crossover. To clarify the situation, we will investigate the light-scattering of solutions of Ionic liquids in solvents of different dielectric constant including hydrocarbons, alcohols and water. Solutions of Ionic Liquids that are able to form liquid crystals will be investigated as in such systems crossover to a tricritical point is quite likely.