Thermal and structural study on liquid-crystalline phase transitions in bis-alkyl trimethyl ammonium dichromates

A series of bis-alkyltrimethylammonium dichromates (CnH2n+1(CH3)(3) N)(2) C r2O7. x H2O (where n = 8, 10, 12, 14, 16, 18, and 0 less than or equal tox less than or equal to2) compounds (ATMACr) was synthesized from alkyltrimet hylammonium bromide and K2Cr2O7. The phase transitions and mesogenicity of these substances were studied by X-ray diffraction, DSC measurements, and F T-IR observations. In the series of hydrated ATMACr compounds, the decreasi ng of the DeltaS(Sm-I) phase transition values with the alkyl chain length n increase, suggest that the disorder in the smectic A phase is dependent o n the carbon. From the temperature dependence of DTMACr IR spectra, the inc rease of the CH2 stretching vibrations frequency and the bandwidth accompan ied by a lowering of the peaks intensity can be ascribed to the introductio n of a high degree of conformational and motional disorders into the alkyl chain.