Structural, Dielectric, and Rheological Characterization of a Thermotropic Polyester Displaying Smectic A, Nematic, and Isotropic Phases

Douglass Kalika, Man Ruo Shen, Xiao Ming Yu, Morton Denn, Pio Iannelli, Norberto Masciocchi, Do Yoon, William Parrish, C. Friedrich, C. Noël

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


We report structural, dielectric, and rheological properties of a thermotropic liquid-crystalline polyester, which exhibits a crystal-crystal transition at 137 °C and crystal-to-smectic A, smectic A-to-nematic, and nematic-to-isotropic transitions at 164, 180, and 220 °C, respectively; initial phase identifications were made by using optical microscopy techniques and confirmed by X-ray diffraction measurements. The dielectric results are highly sensitive to phase state, particularly at the lower frequencies investigated, where interfacial polarization effects dominate due to the broad biphasic regions present in our samples. Higher frequency measurements indicate a sizable increase in dipolar (rotational) mobility at the crystal-crystal transition, no change in the dielectric constant at the crystal-to-smectic A transition, and a decrease in e’ at the onset of the nematic phase. In contrast to the dielectric results, dynamic rheological measurements are insensitive to the crystal-crystal transition, but large, nearly stepwise decreases in complex viscosity are observed across both the crystal-to-smectic A and smectic A-to-nematic transitions, with a slight increase encountered at the onset of isotropy. Constant-temperature frequency sweeps recorded for the smectic A phase indicate a persistent shear thinning behavior, with the storage modulus (C) greater than the loss modulus (G”) over the investigated frequency range. Steady shear viscosity measurements obtained during cooling are consistent with the dynamic results and indicate that the layering of the smectic A phase is apparently not disrupted by steady shearing at low rates. A lack of reversibility is observed for the rheological measurements carried out from 230 °C relative to those initiated at 190 °C; this may be the result of transesterification reactions occurring at the higher temperature.

Original languageEnglish
Pages (from-to)5192-5200
Number of pages9
Issue number25
StatePublished - 1990

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry


Dive into the research topics of 'Structural, Dielectric, and Rheological Characterization of a Thermotropic Polyester Displaying Smectic A, Nematic, and Isotropic Phases'. Together they form a unique fingerprint.

Cite this