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 diffra ction. Measurements were performed by the photographic Guinier method as we ll as by diffractometer on samples aligned on a glass substrate. For a samp le with n = 12, X-ray high-pressure measurements were also performed which allowed us to confirm the destabilization under pressure of the phase exist ing on heating above the first transition point. For all the studied compou nds, except for that with n = 16, strong hysteresis and rich polymorphism w ere observed. A smectic T phase - high-temperature liquid crystal was confi rmed for compounds with n = 16 and 18. All the remaining alkylammonium salt s have smectic an E high-temperature liquid crystal phase.