Liliana C. Tomé

Aqueous biphasic systems: a benign route using cholinium-based ionic liquids

Ionic-liquid-based aqueous biphasic systems (ABS) have been the focus of a significant amount of research in the last decade. However, only (moderately) toxic and poorly biodegradable ionic liquids have been explored hitherto. Focusing on the development of more benign and sustainable approaches, a novel class of ABS using cholinium-based ionic liquids is proposed. For the first time, it is shown that a large assortment of cholinium-based ionic liquids is capable of undergoing liquid–liquid demixing in the presence of aqueous solutions with strong salting-out species. In order to assess the applicability of these systems for separation purposes, the partitioning of two antibiotics and/or their hydrochloride forms was also investigated. Cholinium-based ABS are shown to be improved routes for the extraction of pharmaceuticals, achieving complete extractions in a single-step by way of the proper tailoring of the phase forming components and their concentrations in the aqueous media.

Transparent bionanocomposites with improved properties prepared from acetylated bacterial cellulose and poly(lactic acid) through a simple approach

The preparation and characterization of biocomposite materials with improved properties based on poly(lactic acid) (PLA) and bacterial cellulose, and, for comparative purposes, vegetal cellulose fibers, both in their pristine form or after acetylation, is reported. The composite materials were obtained through the simple and green mechanical compounding of a PLA matrix and bacterial cellulose nanofibrils (or vegetable fibers), and were characterized by TGA, DSC, tensile assays, DMA, SEM and water uptake. The bionanocomposites obtained from PLA and acetylated bacterial cellulose were particularly interesting, given the considerable improvement in thermal and mechanical properties, as evidenced by the significant increase in both elastic and Young moduli, and in the tensile strength (increments of about 100, 40 and 25%, respectively) at very low nanofiller loadings (up to 6%). These nanocomposites also showed low hygroscopicity and considerable transparency, features reported here for the first time.

CO2 separation applying ionic liquid mixtures: the effect of mixing different anions on gas permeation through supported ionic liquid membranes

In order to increase flexibility in tailoring the permeability and selectivity of supported ionic liquid membranes (SILMs) for flue gas separation and natural gas purification, this work explores the use of ionic liquid mixtures. For that purpose, gas permeation properties of CO2, CH4 and N2 in several binary ionic liquid mixtures based on a common cation ([C2mim]+) and different anions such as bis(trifluoromethylsulfonyl)imide ([NTf2]−), acetate ([Ac]−), lactate ([Lac]−), dicyanamide ([DCA]−) and thiocyanate ([SCN]−) were measured at 293 K using a time-lag apparatus. In addition to gas permeation results, the thermophysical properties of those mixtures, namely viscosity and density, were also determined so that trends between the two types of properties could be evaluated. The results show that mixing [Ac]− or [Lac]− with [NTf2]− promotes the decrease of gas permeability and diffusivity of the SILMs based on those binary mixtures, essentially due to their high viscosities. The pure ionic liquids containing anions with nitrile groups, [DCA]− or [SCN]−, and also their mixtures with [C2mim][NTf2] exhibit permselectivities ranging from 19.1 to 23.0 for CO2/CH4, and from 36.6 to 67.8 for CO2/N2, as a consequence of a reduction in the CH4 and N2 permeabilities, respectively. Furthermore, it is shown that mixing anions with different chemical features allows variations in ionic liquid viscosity and molar volume that impact the gas permeation properties of SILMs, offering a clear pathway for the optimization of their CO2 separation performances.

Cholinium-based Supported Ionic Liquid Membranes: A Sustainable Route for Carbon Dioxide Separation

Aiming at full sustainability of CO2 separation processes, a series of supported ionic liquid membranes based on environmentally friendly cholinium carboxylate ionic liquids were successfully prepared. Their gas permeation properties were measured and high permselectivities were obtained for both CO2 /CH4 and CO2 /N2 .

Phosphonium-based ionic liquids as modifiers for biomedical grade poly(vinyl chloride).

This work reports and discusses the influence of four phosphonium-based ionic liquids (PhILs), namely trihexyl(tetradecyl) phosphonium dicyanamide, [P(6,6,6,14)][dca]; trihexyl(tetradecyl) phosphonium bis(trifluoromethylsulfonyl)imide, [P(6,6,6,14)][Tf(2)N]; tetrabutyl phosphonium bromide, [P(4,4,4,4)][Br]; and tetrabutyl phosphonium chloride, [P(4,4,4,4)][Cl], on some of the chemical, physical and biological properties of a biomedical-grade suspension of poly(vinyl chloride) (PVC). The main goal of this work was to evaluate the capacity of these PhILs to modify some of the properties of neat PVC, in particular those that may allow their use as potential alternatives to traditional phthalate-based plasticizers in PVC biomedical applications. PVC films having different PhIL compositions (0, 5, 10 and 20 wt.%) were prepared (by solvent film casting) and characterised by Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, dynamical mechanical thermal analysis, scanning electron microscopy/energy-dispersive X-ray/electron probe microanalysis, X-ray diffraction, transmittance, permeability towards oxygen and carbon dioxide, thermal degradation, contact angle measurement, water and vapour uptake, leachability and biocompatibility (haemolytic potential, thrombogenicity and cytotoxicity). A conventional organic plasticizer (di-isononyl phthalate) was used for comparison purposes. The results obtained showed that it was possible to change the neat PVC hydrophobicity, and consequently its water uptake capacity and plasticizer leachability, just by changing the PhIL employed and its composition. It was also possible to significantly change the thermal and mechanical properties of PVC films by choosing appropriate PhIL cation/anion combinations. However, a specific PhIL may not always be capable of simultaneously keeping and/or improving both physical properties. In addition, ionic halide salts were found to promote PVC dehydrochlorination. Finally, none of the prepared materials presented toxicity against Caco-2 cells, though pure [P(6,6,6,14)][dca] decreased HepG2 cells viability. Moreover, PVC films with [P(6,6,6,14)][dca] and [P(4,4,4,4)][Cl] were found to be haemolytic and thus these PhILs must be avoided as PVC modifiers if biomedical applications are envisaged. In conclusion, from all the PhILs tested, [P(6,6,6,14)][Tf(2)N] showed the most promising results regarding blood compatibility, leaching and permeability to gases of PVC films. The results presented are a strong indicator that adequate PhILs may be successfully employed as PVC multi-functional plasticizers for a wide range of potential applications, including those in the biomedical field.

Turning into poly(ionic liquid)s as a tool for polyimide modification: synthesis, characterization and CO2 separation properties

In an attempt to improve the mechanical and thermal properties of poly(ionic liquid)s (PILs), a new synthetic method for the modification of polyimides is reported here for the first time. The proposed methodology consists of the transformation of polyimides into their ionic forms via subsequent N-alkylation and quaternization of benzimidazole or quinuclidine moieties. Finally, an ion exchange reaction was also carried out in order to prepare polymers bearing the bis(trifluoromethylsulfonyl)imide anion. The elaboration of optimal conditions for the reactions afforded the preparation of high molecular weight (Mn = 2.2–9.7 × 104) cationic polyelectrolytes with a degree of quaternization as high as 96%. Among the unique features of these new PILs are the preservation of excellent mechanical and thermal properties inherent in polyimides, the adjustable surface wettability with variable water contact angles from 70.5 to 94.3°, the enhanced hydrolytic stability (up to 9 h in boiling water) and improved gas transport properties (CO2 permeability up to 28.9 Barrer for a neat film and 85.0 Barrer for a filled membrane at 20 °C and 100 kPa).

Polymeric ionic liquid membranes containing IL–Ag+ for ethylene/ethane separation via olefin-facilitated transport

This work focuses on the separation of light olefins from their corresponding paraffins using membranes due to their lower energy consumption and operating costs in comparison to the traditionally used methods which are highly energy intensive. Although polymeric ionic liquids (PILs) have attracted much attention as interesting materials to prepare improved gas separation membranes, their exploitation for light olefin/paraffin separation has never been attempted before. In this work, we propose the use of PILs as alternative polymer matrices for olefin/paraffin separation. A new series of facilitated transport membranes of poly([pyr11][NTf2]) incorporating different amounts of the ionic liquid ([pyr14][NTf2]) and the silver salt (AgNTf2) were prepared by a film casting process and their ethane and ethylene permeation properties were measured at 293 K using a time-lag apparatus. The results show that the preparation of PIL/IL composite membranes increases the permeability of both C2H4 and C2H6, overcoming the hindered gas diffusion in the pure PIL. Nevertheless, the presence of the IL in the composite membrane promotes reduced C2H4/C2H6 permselectivity. The addition of the silver salt greatly boosts the solubility of the olefin in the membranes. Furthermore, increasing the silver ion concentration in the PIL/40% IL system leads to enhanced overall C2H4/C2H6 permselectivity surpassing the upper bound for polymeric membranes, indicating that PILs have interesting potential as polymer matrices for olefin-facilitated transport membranes.

Bioactive transparent films based on polysaccharides and cholinium carboxylate ionic liquids

Novel antibacterial and biocompatible transparent films based on chitosan or pullulan and two bioactive ionic liquids (ILs), cholinium hexanoate and cholinium citrate, were prepared. These ILs were selected based on their MIC values against several microbial strains, film-forming ability when blended with the polysaccharides and biocompatibility against designated human cell lines. The films were obtained through simple casting of polysaccharide aqueous solutions containing different amounts of the ILs (20 and 40 wt% with respect to the amount of polysaccharide). The physical properties of the films were investigated using transmittance measurements, thermal analysis, mechanical testing and antibacterial assays. In general, the addition of both ILs does not affect the optical transparency (up to 80% transmittance within 400–700 nm) of the films but decreased their stiffness (acting as plasticizers) and thermal stability. All chitosan-based films showed antibacterial activity against S. aureus and K. pneumoniae but for pullulan only those with cholinium citrate were bioactive.

Expanding the Applicability of Poly(Ionic Liquids) in Solid Phase Microextraction: Pyrrolidinium Coatings

Crosslinked pyrrolidinium-based poly(ionic liquids) (Pyrr-PILs) were synthesized through a fast, simple, and solventless photopolymerization scheme, and tested as solid phase microextraction (SPME) sorbents. A series of Pyrr-PILs bearing three different alkyl side chain lengths with two, eight, and fourteen carbons was prepared, characterized, and homogeneously coated on a steel wire by using a very simple procedure. The resulting coatings showed a high thermal stability, with decomposition temperatures above 350 °C, excellent film stability, and lifetime of over 100 injections. The performance of these PIL-based SPME fibers was evaluated using a mixture of eleven organic compounds with different molar volumes and chemical functionalities (alcohols, ketones, and monoterpenes). The Pyrr-PIL fibers were obtained as dense film coatings, with 67 μm thickness, with an overall sorption increase of 90% and 55% as compared to commercial fibers of Polyacrylate (85 μm) (PA85) and Polydimethylsiloxane (7 μm) (PDMS7) coatings, respectively. A urine sample doped with the sample mixture was used to study the matrix effect and establish relative recoveries, which ranged from 60.2% to 104.1%.