Self-assembled liquid crystals by hydrogen bonding between bipyridyl and alkylbenzoic acids: solvent-free synthesis by mechanochemistry |
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| Authors: | Micael D Miranda Fabián Vaca Chávez Teresa MR Maria M Ermelinda S Eusebio PJ Sebastião Manuela Ramos Silva |
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| Institution: | 1. European Space Agency, Noordwijk, The Netherlands;2. CEMDRX, Physics Department, University of Coimbra, Coimbra, Portugalmmiranda@teor.fis.uc.pt;4. Condensed Matter Physics Centre, Universidade de Lisboa, Lisboa, Portugal;5. Department of Physics, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal;6. CQC, Chemistry Department, University of Coimbra, Coimbra, Portugal;7. CEMDRX, Physics Department, University of Coimbra, Coimbra, Portugal |
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| Abstract: | A series of thermotropic hydrogen-bonded liquid crystalline structures based on 4,4′-bipyridyl and aliphatic carboxylic acids was prepared by a mechanosynthesis technique. This series was characterised by polarising optical microscope, differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray powder diffraction and 1H NMR relaxometry experimental techniques. In these complexes, the bipyridyl component, a non-mesogenic substance by itself, acts as a double H-bond acceptor, whereas the alkylbenzoic acid acts as a H-bond donor, in a 1:2 proportion. The so-formed complexes exhibit mesophases that are not observed by the single components. A characteristic phase (smectic A) is identified and shown to be affected by the alkyl chain length. The isotropisation temperature is increased by the supramolecular aggregation through the H-bonds. |
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| Keywords: | hydrogen-bonded liquid crystals FTIR 4-alkylbenzoic acids 4 4′-bipyridyl field-cycling NMR relaxometry mechanochemistry |
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