Ionic Liquid Crystals: From Fundamental Studies to Applications
By: Andreia Santos
From: LAQV-REQUIMTE, Department of Chemistry, NOVA School of Science and Technology, NOVA University of Lisbon, Portugal
At: Building C1, room 1.4.14
[2024-12-16]
Ionic liquids (ILs), i.e., organic salts with low melting point, have proven to be useful in a wide range of applications, from tailor-made solvents (the first generation of ionic liquids) to advanced materials (second generation) and pharmaceuticals (third generation), due to the wise pairing of their cations and anions, allowing for the modulation of the compound’s final properties. This fine tuning, extremely relevant in several fields, is addressed by the vast diversity of ions that can be incorporated in ionic
liquids. Within the framework of the second generation, ionic liquid crystals (ILCs) have emerged as promising candidates for different applications, combining the characteristics of ionic liquids and liquid crystals.
Recently, a new family of ILCs based on pyridinium and methylpyridinium cations was developed. In
this seminar, an overview will be provided of how ionic liquid crystals can be sustainably synthesised and characterised [1?3]. These fundamental works show how mesomorphism and conductivity can be affected by small structural changes in terms of the methyl group position (ortho-, meta- and para-) and the alkyl chain length (C6, C12 and C16). Furthermore, two different strategies to improve the material’s performance near room temperature will be discussed: i) confinement into organic and inorganic [4] matrices to obtain a composite with enhanced properties; ii) lyotropic systems to bring the mesophase, occurring above 80 °C, down to room temperature [5]. Both strategies can be extrapolated for other materials and different purposes. Finally, taking advantage of the ILC’s fine tuning, this seminar will also address the potential of such pyridinium and picolinium ILCs for chromogenic materials [6], i.e., materials that change colour upon an external stimulus, by developing intrinsically electro- and photochromic compounds based on vanadate and methyl orange, respectively, as well as task-specific electrolytes to dissolve responsive probes.
This presentation will demonstrate the versatility of ionic liquid crystals, in which the synthesised organic salts acted as model compounds to evaluate the correlation between chemical structure, phase transitions and conductivity behaviour, guiding also the future design of sustainable electronic and smart materials.
References:
[1] A. F. M. Santos, C. Cruz, M. H. Godinho, M. Dionísio, J. L. Figueirinhas and L. C. Branco, “Synthesis and
characterisation of ionic liquid crystals based on substituted pyridinium cations”, Liquid Crystals, 2022, 49 (13), 1809–1821. DOI: 10.1080/02678292.2022.2070783
[2] A. F. M. Santos, J. L. Figueirinhas, C. J. Dias, M. H. Godinho, L. C. Branco and M. Dionísio, “Study of the
mesomorphic properties and conductivity of n-alkyl-2-picolinium ionic liquid crystals”, Journal of Molecular Liquids, 2023, 377, 121456. DOI: 10.1016/j.molliq.2023.121456
[3] A. F. M. Santos, “Development of ionic liquid crystals based on pyridinium and picolinium cations”, Liquid Crystals Today, 2023, 32 (1), 4–11. [cover] DOI: 10.1080/1358314X.2023.2221615
[4] A. F. M. Santos, M. T. Viciosa, I. Matos, J. C. Sotomayor, J. L. Figueirinhas, M. H. Godinho, L. C. Branco,
C. J. Dias and M. Dionísio, “Impact of nanoconfinement on the physical state and conductivity mechanisms of a 2-picolinium ionic liquid crystal”, Journal of Molecular Liquids, 2024, 403, 124830. DOI:
10.1016/j.molliq.2024.124830
[5] A. F. M. Santos, A. Gradišek, T. Apih, P. J. Sebastião, M. Dionísio, L. C. Branco, J. L. Figueirinhas and M.
H. Godinho, “Lyotropic Aqueous 2-Picolinium Ionic Liquid Crystals and Their Shear-Induced Foams”,
Langmuir, 2024, 40 (38), 19964–19971. [cover] DOI: 10.1021/acs.langmuir.4c02059
[6] A. F. M. Santos, J. L. Figueirinhas, M. Dionísio, M. H. Godinho and L. C. Branco, “Ionic Liquid Crystals as Chromogenic Materials”, Materials, 2024, 17 (18), 4563. DOI: 10.3390/ma17184563
Project UIDB/00618/2020 https://doi.org/10.54499/UIDB/00618/2020