Relation between the Spontaneous Polarization and Alkyl Chain Length in Ferroelectric Switching of Columnar Liquid-Crystalline Ureas.

Relation between the spontaneous polarization and alkyl chain length was investigated in ferroelectric switching of N,N'-bis(3,4,5-trialkoxyphenyl)urea (1-7) possessing n-C4H9, n-C8H17, n-C9H19, n-C10H21, n-C11H23, n-C12H25, and n-C16H33, respectively. The phase behaviors were investigated by differential scanning calorimetry, polarized optical microscopy, and the column diameters were obtained by X-ray diffraction. Compound 2-7 exhibited rectangular and hexagonal columnar phases. All of the hexagonal columnar phases showed ferroelectric switching under a triangular wave voltage. From the plot of the spontaneous polarization against the carbon atom number of the alkyl chains, correlation between them were clarified and it was strongly suggested that the switching current peaks originated in switching of the polar columns, not in the movement of ionic impurities. [ABSTRACT FROM AUTHOR]