Mesophase assembling by H-bonding in the 4-(octyloxy)benzoic/4-alkylbenzoic acids series

T. M MARIA; M. MIRANDA; P. MARTIN-RAMOS; F. VACA CHAVEZ; M. EUSEBIO; PEDRO J. SEBASTIÃO; J. FIGUERINHAS; M. RAMOS SILVA

Congreso; 41st Conference o Phase Equilibria; 2015

The design of hydrogen-bonded liquid crystals (HBLCs) with non-covalent interactions is a possibility that has drawn the attention of researchers towards the synthesis of self-assembly systems. A successful HBLC requires not only a complementarity of the interacting components (H-bond donor and H-bond acceptor), but also a certain magnitude and direction of the H-bonds. In the present study, a molecular recognition process between different molecular species has been successfully used to form new mesogenic molecular structures where the intermolecular hydrogen bonding occurs between 4-(octyloxy)benzoic acid (8BAO) and four different 4-alkylbenzoic acids (nBAs, where n=2, 5, 6, 7), resulting in the formation of new HBLCs. The synthesis of the four HBLCs under study has been attained by a Green Chemistry method, avoiding the need for solvents: a mechanochemistry approach has been chosen, using a ball mill system.1 The resulting series of materials has been characterized by polarizing optical microscopy, differential scanning calorimetry, vibrational spectroscopy, X-ray powder diffraction and 1H NMR relaxometry. These results will be presented and discussed. The 8BAO+nBA co-crystals under study show a good thermal and chemical stability upon several heating/cooling cycles. They all exhibit a mesophase at temperatures from approximately 50ºC to 130ºC. For one of the new materials (8BAO+7BA), electro-optical measurements have also been conducted so as to assess its performance vs. other well-known liquid crystals. (1) M.C. Miranda, F.Vaca Chávez, T.M.R. Maria, M.E.S. Eusébio, P.J. Sebastião, M, Ramos Silva, Liquid Crystals, 41, 2014, 1743-1751.