Dielectric relaxation of thermotropic liquid crystalline polyesters based on α,ω,-alkylene-di-4-hydroxybenzoates and 4,4’-alkylenedioxy-dibenzoic acid
| Autor: | Giancarlo Galli, Giuseppe Salvetti, Emo Chiellini, Elizabeth Grillo Fernandes, Elpidio Tombari |
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| Jazyk: | English, Middle (1100-1500) |
| Rok vydání: | 2018 |
| Předmět: |
Dielectric spectroscopy
Materials science 02 engineering and technology Dielectric WLF 01 natural sciences Thermotropic crystal Thermotropic liquid crystal Homologous series chemistry.chemical_compound Polymer chemistry Physical and Theoretical Chemistry Polymer Hydroxybenzoates 021001 nanoscience & nanotechnology Condensed Matter Physics Polymer Thermotropic liquid crystal Dielectric spectroscopy WLF 010406 physical chemistry 0104 chemical sciences Crystallography chemistry Relaxation (physics) Dielectric loss 0210 nano-technology Glass transition |
| Popis: | Two structurally isomeric homologous series of semiflexible thermotropic liquid crystalline polyesters were analysed by dielectric spectroscopy in temperature intervals varying from 253 to 403 K. Each series is characterised by a well-distinct behaviour of the dielectric loss versus temperature with a minor diffuse and a more confined relaxation occurring at lower and higher temperatures, respectively. Extrapolations from semilog plots of frequency (f) versus reciprocal absolute temperature (1/T) indicated that the principal relaxation is related to the glass transition temperature as defined by DSC. The analysis of data according to WLF equation indicated that the size and the kind of the polymethylene groups influence the apparent activation energy. A parity effect, connected to the length of polymethylene segments within each series, was finally detected on the relative position of the maximum relaxation, the odd numbers showing in any case higher temperature values. |
| Databáze: | OpenAIRE |
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