Optical Proof of Mesophase Transitions between Smectic and Nematic Phase of the Side-Group Polyacrylate PAC6

The liquid-crystalline side-group polyacrylate PAC6 forms two mesophases in thin layers within the temperature range between 90 and 100 °C. The structures developing by self-organization can be made clearly visible by Schlieren-optical methods. If a low lateral temperature gradient is maintained in the temperature range mentioned above one can simultaneously and abreast observe four phases in PAC6 layers. Both new phases occur between the smectic and the nematic phase. Layer surface deformations arise during this phase transition. They were analyzed with a microscope interferometer. The PAC6 melt shows a considerable change of surface tension in this temperature range.

Schlieren-optical image of a PAC6 layer with two mesophases.