Joint research project

Experimental and Computational studies of polymeric membranes based on ionic liquid crystals for preparation of stimuli-responsive materials

Project leaders
Giacomo Saielli, Yanting Wang
Agreement
CINA - CAS (Nuovo Accordo) - Chinese Academy of Sciences
Call
CNR-CAS 2017-2019
Department
Chemical sciences and materials technology
Thematic area
Chemical sciences and materials technology
Status of the project
Extended
Report for renewal
finalreportfirmatodatato-23092016.pdf

Research proposal

INTRODUCTION. Ionic liquid crystals (ILCs) have attracted much attention in recent years as materials that combine the unique solvent properties of Ionic Liquids (ILs) with the long-range partial order of Liquid Crystals (LCs) [1]. The state of the art in the field has been recently reviewed in Ref. [1] where it is also described in details which are the potential uses of ILCs (e.g. as electrolytes in dye-sensitized solar cells[2], electrofluorescence switches [3], electrolytes for Li-ion batteries [4] and electrochemical sensors [5], to mention but a few). In the review the Authors highlight also and the necessity of more computational studies on the subject, which are still quite scarce.
Also, constraint effects on reorganization and phase transitions of ILCs inside polymeric films is considered of great interest for the key role that they may have in the adjustment of intrinsic properties of the hosting materials. Few reports in the literature have addressed this problem; among them in the work of Kohler et al. [6] it was investigated the effect of confinement of a ILC in Si-based porous powders while Uchida and coworkers studied the effect of confinement of ILCs in inorganic membranes base on aluminum oxide with cylindrical pores [7].
This project is continuing and advancing a successful cooperation between the CNR Unit and the CAS Unit. The results of the previous three-year bilateral project (2014-2016) have been described in details in the Final Report attached to this submission; such Report is an integral part of this new project. In short, we have significantly advanced our understanding of the structural and dynamic properties of ILCs in bulk, through synthesis, experiments and simulations, and we have prepared polymeric membranes based on viologen salts with improved properties (see the list of publications in the Final Report file, Sec. 7). Our work will be now extended by testing systematically other ILCs compounds in dense polymeric membranes and it will be complemented by MD simulations with novel Force Fields developed by the CAS Unit. The interplay between simulations and experiments will enable us to optimize the performance of the systems prepared through in-depth understanding of structure-properties relationships with a special focus on the capability of ILCs to provide controlled permeability through membranes.

RESEARCH PROPOSAL. Viologen based ILCs have shown a rich polymorphism. In addition to the crystal phase and to the isotropic phase we have found at least two ionic liquid crystal phases. A high temperature SmA phase and a low temperature more ordered phase that we have described, based on spectroscopic evidence, as an alternation of molten hydrophobic layers (essentially made of alkyl chains) and weakly ordered ionic layers, see the Final Report, refs. [1-2]. The occurrence of phase transitions between crystal and a liquid crystal phase, preferably within the range of 25 to 65 °C, will be exploited to build dense polymeric membranes with temperature dependence in their transport properties depending on the phase of the embedded ILC.
To achieve an optimal performance of the device it is necessary to have several parameters to play with. On the one hand the ILC component: it is necessary to be able to modulate its hydrophilic/lipophilic balance in order to obtain the best performance in terms of water solubility and diffusion. To this end ILCs, being composed of the same type of cations and anions as usually found in ILs, are the best choice since we have the opportunity to vary, to some extent, cation and anion type, and the length of the lateral chains for a fine tuning of their properties. On the other hand, the liquid crystallinity of these samples is necessary in order to have a partially ordered yet still fluid phase, to allow a significant transport of mass and/or charge through the membrane. Finally, the transition temperatures between crystal and smectic phase will represent the on-off switch to make a responsive membrane. Again, it is possible to finely tune the transition temperatures of the ILCs by an appropriate choice of alkyl chain length and type, that is using alkyl, polyfluorinated or polyether chains of varying C atoms. Concerning the hosting polymeric membrane, some classes of materials, including elastomers and perfluorinated polymers, poly(etheramide) and acetate, will be considered with the intent to evaluate effects of compatibility and capability of ILCs to rearrange themselves inside hosting matrixes.
In parallel with our experimental studies the CAS Unit will be involved in the development of specific Force Fields for the simulations of ILC phases of viologens with alkyl (a task already accomplished in the previous project), polyfluorinated and polyether chains and their corresponding coarse-grained version and for the description of the polymeric membranes investigate by the CNR Unit. This task is described in details in the companion project of the CAS Unit.

REASONS FOR THE COOPERATION. The CNR Unit does not have the expertise neither for developing new Force Fields (FF) nor for coarse-graining fully atomistic FF into their Coarse Grained version. On the other hand, the CNR Unit has the expertise for the synthesis, preparation and characterization of ILCs and membranes and for the MD simulations of ILC and polymeric membranes using FF found in the literature. For these reasons we believe that the CNR and CAS Units are perfectly matching in terms of competencies and contributions they will give to the realization of the project.

REFERENCES
[1] K. Goossens et al., Chem. Rev. 2016, 116, 4643
[2] N. Yamanaka, et al., J Phys Chem B, 2007, 111, 4763
[3] Beneduci, A. et al. Nat. Commun. 2014, 5.
[4] Yoshio, M. et al. J. Am. Chem. Soc. 2006, 128, 5570.
[5] Safavi A. et al. J. Phys. Chem. C 2010, 114, 6132.
[6] Kohler F.T. et al. ChemPhysChem 2011, 12, 3539.
[7] Y. Uchida et al. J. Mater. Chem. C 2015, 3, 6144.

Research goals

The main goal of this project is the preparation of dense polymeric membranes with embedded ILCs that will exhibit an on-off behavior as a function of the temperature concerning the permeability to water vapor. The on-off behavior will be a results of a phase transition of the ILC embedded in the polymer (crystal-to-liquid crystal transition and viceversa). As mentioned in the Introduction above, conductive properties of partially ordered LC phases are significantly different from the same properties in crystalline phases and, in addition, confinement effects are extremely important as well (see Refs. [6] and [7] of the Introduction). These features will be exploited in order to prepare the responsive materials. To this end we will synthesize several type of ILCs optimizing their properties such as transition temperature, solubility, processability and miscibility with the hosting polymeric matrix. Several types of polymers, including poly(etheramide), acetate and fluorinated derivatives, will be chosen to prepare membranes embedding a significant amount of ILCs. Reproducibility and reversibility of water vapor transport properties through ILCs-based membranes will be investigated as well.
In order to gain an understanding of the structure of the dense membrane, MD simulations will be employed, both at the fully atomistic as well as coarse-grained level, using the Force Fields developed by the CAS Unit and in collaboration with the chinese counterpart.

Last update: 29/03/2024