X-ray investigation of dialkyldimethylammonium bromides

A Series of dialkyldimethylammonium bromides (DDAB), (CnH2n + (1))(2)N+(CM3)(2)Br- with n = 10, 12, 14, 16 and 18 were investigated using X-ray diffraction. Measurements were performed by the photographic Guinier method as well as by diffractometer on samples aligned on a glass substrate. For a sample with n = 12, X-ray high-pressure measurements were also performed which allowed us to confirm the destabilization under pressure of the phase existing on heating above the first transition point. For all the studied compounds, except for that with n = 16, strong hysteresis and rich polymorphism were observed. A smectic T phase - high-temperature liquid crystal was confirmed for compounds with n = 16 and 18. All the remaining alkylammonium salts have smectic an E high-temperature liquid crystal phase.