| Autor: |
M. E. Neubert, Y. Dixon-Polverine, C.-C. Tsai, T. T. Blair, M. Tsai |
| Rok vydání: |
1990 |
| Předmět: |
|
| Zdroj: |
Molecular Crystals and Liquid Crystals. 182:269-286 |
| ISSN: |
1542-1406 |
| DOI: |
10.1080/00268949008035758 |
| Popis: |
Transition temperatures for all known 4,4'-alkyl/alkoxyphenylbenzoates were collected into a computer data base. Trends in mesomorphic properties in these esters were reevaluated by comparing line graphs of melting and clearing temperatures and bar graphs showing all mesophases for the four different homologous series, holding first the acid chain constant and then the phenolic chain. Overall views of these series in which X and Y were varied simultaneously were obtained from two dimensional block diagrams of mesophases and three dimensional plots of melting and clearing temperatures. Although transition temperatures usually increased in the order ROR'>RR'>OR'>R' this was not always true for a particular homolog with either R or R' constant. Nematic phases occurred the most often. Its incidence was not affected much by the presence of alkoxy groups although this group on the phenolic side gave more nematic phases. Transition temperatures and phase lengths increased and more mesophases were enantiotropic when alkoxy groups were present. The dialkoxy series showed the most polymorphism and the longest range mesophases. Smectic A phases were favored by an alkoxy group on the acid side whereas smectic C phases were favored by an alkoxy group on the phenolic side and considerably more so by two alkoxy groups. Smectic B phases occurred in all four series, seemingly little affected by the presence of alkoxy groups but requiring at least one long terminal chain. A chain length of at least six carbon atoms on the acid side is needed to observe a smectic phase of any type in all four series. Mesomorphic properties were retained for a longer chain length in a homologous series in the order of ROR'>RR', OR'>R'. Data for a few new esters and some old ones that were rechecked are given. Predictions of mesomorphis properties for the new esters were made and compared with the observed values. Melting temperatures were predicted within the range of ±0.8 to 11.9 o and clearing temperatures in the range of ±0.0 to 5.7 o . Mesophases were predicted correctly in 65% of these esters |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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