Glass transition in liquid crystalline compounds and their mixtures

by Aleksandra Deptuch (IFJ PAN)

Thursday 16 Feb 2023, 11:00 → 13:00 Europe/Warsaw

Liquid crystals (LCs) belong to mesophases, which are thermodynamic states that can exist between isotropic liquid and a solid crystal. LCs possess the long-range orientational order, while the positional order is lower than in solid crystals (only short-range or quasi-long-range). If the LC substance is intended for practical applications, it should not undergo crystallization in a considered temperature range. This is why the influence of the molecular structure on the crystallization process is the important part of LC research. Herein, there are presented results for LC compounds from the mX1X26 family, which form the high-tilted smectic CA* phase suitable for application in LC displays. It is shown that both the length of the CmH2m chain and fluorosubstitution of one of the benzene rings (X1, X2 = H or F) have a significant impact on tendency to either crystallization or formation of the LC glass on cooling at various rates. However, all investigated glassforming mX1X26 compounds form a crystal phase in the process of cold crystallization, which is crystallization that happens during heating from the glassy state. The situation is different for two LC mixtures containing mX1X26 components, because the crystallization is absent both on cooling and on heating, making the investigated mixtures unharmed by temporary exposure to low temperatures.