Ionic liquids and the future of soft materials

Ionic liquid (ILs) offer a versatile platform for designing supramolecular architectures through the manipulation of covalent, ionic, and hydrogen bonds, along with Van der Waals interactions. This is especially true for ILs containing planar and rigid cations. The structural organisation of these materials arises from the supramolecular association of contact ion pairs through cooperative hydrogen bonds and Van der Waals interactions, forming well-defined supramolecular structures with predictable functions. This structural arrangement is observed across solid, liquid, gas phases, and even in solution. These supramolecular structures adapt and are adaptable, allowing for the incorporation of molecular, ionic, macromolecular, and inorganic materials to form inclusion compounds, aggregates, clusters, triple ions, contact ion pairs, and, at high dilutions, solvent-separated ion pairs. These interactions occur with minimal changes to their supramolecular organisation. This presentation delves into the rich and complex chemistry of ILs, drawing on the vast data accumulated over the last 30 years. It considers various aspects beyond the basic interactions between cations and anions, demonstrating that the properties and applications of ILs extend far beyond their fundamental ionic nature.

Professor Jairton Dupont, Universidade Federal do Rio Grande do Sul, Brazil

Professor Jairton Dupont, Universidade Federal do Rio Grande do Sul, Brazil

Jairton Dupont earned his PhD in Chemistry from Université Louis Pasteur, Strasbourg. After postdoctoral work at Oxford, he joined the Federal University of Rio Grande do Sul in 1990, becoming a Professor in 2008. He was EPSRC/GSK Chair in Green and Sustainable chemistry at the University of Nottingham (2014–2017) and later returned to Porto Alegre. His research focuses on ionic liquids applied to green and sustainable chemistry. 

Ionic liquid gels are a versatile class of material that allow a tailored approach to materials design.

Ionic liquid gels of different types will be introduced, including examples of inorganic oxide, supramolecular, organic fossil-based polymer, and biopolymer ionic liquid gels. 

Examples of applications for each type of material, alongside how the material is designed to enhance that application, will be explored. 

The emergence of wholly biobased ionic liquid gels, where both the liquid and solid component of the gel can be bioderived, shows that ionic liquid gels can be both high performance and sustainable materials.  

Dr Patricia Marr, Queen's University Belfast, UK

Dr Patricia Marr, Queen's University Belfast, UK

Dr Patricia C Marr is a senior lecturer at the School of Chemistry and Chemical Engineering, Queen's University Belfast. She developed her keen interest in hybrid functional materials during her PhD studies in The University of St Andrews, and learnt about green chemistry, supercritical CO₂ and green materials whilst she was a PDRA in The University of Nottingham. After another PDRA in the Bristol Colloids Centre Patricia moved to Queen's Belfast and added ionic liquids into the mix. These experiences gelled into an interest in greener materials with bespoke functionality. A particular passion has been the emerging discipline of ionic liquid gels. PCM made her first ionic liquid silica gel in 2003, and has since worked on metal oxide, supramolecular and polymer ionic liquid gels.  

With the widespread use of batteries, their increased performance and safety is of growing importance. While looking for enhanced energy and power, as well as naturally abundant, eco-friendly and cheaper elements, one avenue for this is the enhancement of ion diffusion, particularly for efficient and safe solid-state-like electrolytes, and for different ions such as lithium (Li⁺) and magnesium (Mg²⁺), sodium (Na⁺), zinc (Zn²⁺).1 Unravelling the origin of better cation diffusion in confined ionic liquids (ILs) in a polymer matrix (ionogels) was compared to that of the IL itself. Ionic conductivity measured by EIS for ionogels (7.0 mS.cm-1 at 30°C) is very close to the conductivity of the non-confined IL (8.9 mS.cm-1 at 30°C), ie 1-ethyl-3-methyimidazolium bis(trifluorosulfonyl)imide (EMIM TFSI). An even better ionic conductivity was observed for confined EMIM TFSI with high concentrations (1M) of lithium or magnesium salt added. The improved macroscopic transport properties could be explained by the higher self-diffusion, measured by PFG NMR, of each ion at the liquid-to-solid interface induced by the confinement in poly-vinylidenedifluoride (PVDF) or EO-based polymer (in this last case with phosphonium-FSI-Li) polymer matrix. Upon confinement, the strong breaking down of ion aggregates enables a better diffusion especially for TFSI anion and strongly polarising cations (eg Li⁺, Mg²⁺). The coordination number, obtained by in-depth Raman study, of these cations in the liquid phase confirmed that metal cations interact with the polymer matrix. Moreover, from the NMR study, it is a major result that the activation energy for diffusion is lowered.

Professor Jean le Bideau, Nantes Université, France

Professor Jean le Bideau, Nantes Université, France

Jean Le Bideau is Professor at Institut des Matériaux de Nantes Jean Rouxel (IMN), at Nantes University, where he is Principal Investigator for research on ionogels and hydrogels. His current research focuses on the effect of the chemical and topological nature of the confining network on the dynamics of the confined liquid. The fields of applications more particularly targeted are the electrochemical energy storage and the tissue engineering for regenerative medicine.

Hydrogen bonding (H-bonding) is present in many ionic liquids (ILs), IL-like materials and deep eutectic solvents, and can play a key role in determining the chemical and physical properties of these materials. The range and versatility of ILs is, in-part, due to the diverse range of H-bonding interactions that occur within different ILs. This extends from ILs that barely exhibit H-bonding (and resemble molten salts) to ILs that are formed by the transfer of a proton and exist in equilibrium with the corresponding neutral acid and base (protic ILs).

There is an increasing interest in bio-derived and/or bio-compatible IL materials. This includes ILs based on bio-relevant cations with (protic) N-H or (aprotic) C-H moieties such as imidazolium, ammonium, guanidinium or choline and/or anions which are principally (natural) carboxylates. In poly-ILs either the bio-relevant cation or anion can be polymerised or included as pendant groups on a polymer chain. There is significant interest in the ability of such bio-ILs to; stabilise proteins, enhance the activity of nano-particles for bio-applications, be more sustainable proton conductors for fuel cells and non-toxic electrolytes for (wearable) devices.

The general nature of a simple "ordinary" H-bond formed within an aqueous environment is well known.  However, in IL and IL-like systems the ionic nature of the H-bonded pairs and dense ionic solvent environment leads to the formation of "doubly ionic H-bonds" that have key differences with respect to more traditional H-bonds. In an environment with many H-bond donors and acceptors full proton transfer is also relevant, but can be unconventional. With very limited molar quantities of water, hydronium ions cannot form and the pH can be different from that anticipated based on aqueous solutions. Moreover, the pKa of the constituent ions can differ from that expected. Thus, there are many open questions on the nature of H-bonds within bio-IL systems.

The aim of this presentation is to explore the H-bond that forms in bio-ILs and IL-like materials through the lens of molecular quantum chemical (DFT) calculations. The fundamental molecular level inter-ion interactions that occur, and the electronic structure of the H-bonds that form, will be considered.

Professor Patricia Hunt, Victoria University of Wellington, New Zealand

Professor Patricia Hunt, Victoria University of Wellington, New Zealand

Research in the Hunt group spans liquids and solvation (ionic liquids, molten salts, aqueous systems and deep eutectic solvents), catalysis (mechanisms and reactivity), bonding (H-bonding, MO theory, ESP analysis) and theory development. A unifying theme is the use and application of computational modelling employing quantum chemical methods. A key area of research is the application of computational methods to probe and understand the molecular and electronic structure of ionic liquids, and ionic liquid like systems.  

Glasses and gels are usually considered distinct classes of materials. Glassy polymers are generally hard (high modulus), possess a glass transition temperature, and are often brittle. Gels are polymer networks swollen with liquid. Usually, the presence of solvent in a crosslinked polymer network causes it to swell, thereby significantly decreasing the modulus and significantly increasing the strain at break. We discovered a class of materials that we call “glassy gels” that contain up to 60% liquid, yet have glassy mechanical properties. The solvent in this case is an ionic liquid, which acts as noncovalent crosslinker between chains, restricting the movement of the polymer chains, thereby making the gel glassy at room temperature, resulting in an ultrahigh modulus (~1 GPa) and exceptional toughness, similar to thermoplastics. Yet unlike thermoplastics, which typically form using specialised catalysts and elevated temperatures, these “glassy gels” can form easily by mixing the ingredients and curing it with light via free radical polymerisation. In addition, the glassy gels have useful properties such as self-healing, shape memory, and exceptionally strong adhesion to many surfaces despite being glassy. The findings should expand the applications of ionogels, which are compelling materials for energy storage devices, ionotronics, and actuators due to their excellent ionic conductivity, thermal and electrochemical stability and nonvolatility. 

Professor Michael Dickey, North Carolina State University, USA

Professor Michael Dickey, North Carolina State University, USA

Michael Dickey received a BS in Chemical Engineering from Georgia Institute of Technology (1999) and a PhD from the University of Texas (2006) under the guidance of Professor Grant Willson. From 2006-2008 he was a post-doctoral fellow in the lab of Professor George Whitesides at Harvard University. He is currently the Camille and Henry Dreyfus Professor in the Department of Chemical & Biomolecular Engineering at North Carolina State University. He completed a sabbatical at Microsoft in 2016 and EPFL in 2023. Michael’s research interests include soft matter (liquid metals, gels, polymers) for soft and stretchable devices (electronics, energy harvesters, textiles, and soft robotics).

Since their first appearance in literature, ionic liquids have immediately shown their potential from an applicative point of view. Thanks to their structural tunability, allowing the modulation of their properties, they have been used in different fields. 

This lecture will analyse their confinement in the ionic liquid gels. These are soft materials exhibiting intermediate behaviour between solid and liquid systems. They can be obtained from the entrapment of ionic liquids in a three-dimensional network formed by low molecular weight compounds or polymeric species. Consequently, changing the nature of the ionic liquids, a fine tuning of the soft materials properties can be obtained.

In the light of the above considerations, the lecture will firstly focus on the analysis of the relationship working between ionic liquids structure and gel properties. Then, the obtainment of hybrid ionic liquid gels, deriving from the combination with carbon nanomaterials will be discussed. Finally, a wide overview of the applications, spanning from the use as reaction media, to the ones of materials for wastewater treatment or desulfurization of fuels, as well as the one as antioxidant and antibacterial coatings or system for chiral selection will be discussed.

Professor Francesca D'Anna FRS, University of Palermo, Italy

Professor Francesca D'Anna FRS, University of Palermo, Italy

Francesca D’Anna is Full Professor of Organic Chemistry at the University of Palermo (Italy). Her main research interests deal with the study of properties and application of non- conventional solvents, like ionic liquids and deep eutectic solvents. In her research activity, she conjugates the attention for green and sustainable chemistry with the one in supramolecular chemistry. She is author of more than 140 papers on ISI journal, with a Hindex of 36. She is serving as Coordinator of the Bachelor and master’s degree in chemistry at the University of Palermo. She is currently Fellow of the Royal Society and Vice President of the Organic Chemistry Division of the Italian Chemical Society.

Ionic Liquids offer exciting opportunities for several therapeutic applications. Their tuneable properties offer control over their design and function. Starting with biocompatible ions, we synthesised a library of ionic liquids and explored them for various drug delivery applications. Ionic liquids provided unique advantages including overcoming the biological transport barriers of skin, buccal mucosa, subcutaneous tissue and the intestinal epithelium, among others. At the same time, they also stabilised proteins and nucleic acids, and enabled the delivery of biologics across these barriers. They also provided unique biological functions including adjuvancy towards vaccines and antimicrobial function. I will present an overview of the design features of ionic liquids and novel therapeutic applications enabled by these unique materials.

Professor Samir Mitragotri, Harvard University, USA

Professor Samir Mitragotri, Harvard University, USA

Samir Mitragotri is the Hiller Professor of Bioengineering and Wyss Professor of Biologically Inspired Engineering at Harvard University. His research is focused on drug delivery. His research has led to new technologies for transdermal, oral, and targeted drug delivery systems. He is an elected member of the National Academy of Engineering, National Academy of Medicine and National Academy of Inventors. He is an author on over 400 publications and an inventor on over 300 patents/patent applications. He is also an elected fellow of AAAS, CRS, BMES, AIMBE, and AAPS. He received BS in Chemical Engineering from the Institute of Chemical Technology, India and PhD in Chemical Engineering from the Massachusetts Institute of Technology.