Effect of ionic liquid anion and cation on the physico-chemical properties of poly(vinylidene fluoride)/ionic liquid blends

Deep eutectic solvent-based blended membranes for ultra-super selective separation of SO2

SO2 is a major atmospheric pollutant leading to acid rain and smog. As a new generation of green solvents, deep eutectic solvents (DESs) have been widely investigated for gas capture. Nevertheless, studies on DES-based membranes for SO2 separation are yet minimal. Herein, we devised polymer/DES blended membranes comprising 1-butyl-3-methyl-imidazolium bromide ([Bmim]Br)/diethylene glycol (DEG) DES and poly (vinylidene fluoride) (PVDF), and these membranes were firstly used for selective separation of SO2 from N2 and CO2. The permeability of SO2 reaches up to 17480 Barrer (0.20 bar, 40 ºC) in PVDF/DES blended membrane containing 50 wt% of [Bmim]Br/DEG (2:1), with ultrahigh SO2/N2 and SO2/CO2 selectivity of 3690 and 211 obtained, respectively, far exceeding those in the state-of-the-art membranes reported in literature. The highly-reversible multi-site interaction between SO2 and [Bmim]Br/DEG DES was revealed by spectroscopic analysis. Furthermore, the PVDF/DES blended membrane was also able to efficiently and stably separate SO2/CO2/N2 (2.5/15/82.5%) mixed gas for at least 100 h. This work demonstrates for the first time that [Bmim]Br-based DESs are very efficient media for membrane separation of SO2. The easy preparation, low cost and high performance enable polymer/DES blended membranes to be promising candidates for flue gas desulfurization.

Ion Transport in the EMITFSI/PVDF System at Different Temperatures: A Molecular Dynamics Simulation

We used all-atom molecular dynamics simulations to study the ion transport in the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/poly(vinylidene fluoride) (EMITFSI/PVDF) system with 40.05 wt % EMITFSI at different temperatures. The glass-transition temperature (T _g = 204 K) of this system shows a good agreement with the experimental value (200 K). With the increase of temperature, the peaks of the pair correlation function show an increasing trend. Interestingly, the coordination numbers of ion pairs and the degree of independent ion motion are mainly affected by the binding energy between ion pairs as the temperature increases. In addition, the ion transport properties with increasing temperature can be studied by the ion-pair relaxation times, ion-pair lifetimes, and diffusion coefficients. The simulation results illustrate that the ion transport is intensified. Especially, the cations can always diffuse faster than the anions. The power law shows that mobilities of anions and cations are seen to exhibit a "superionic" behavior. With the increase of temperature, transference numbers of anions decrease first and then increase and transference numbers of cations show the opposite changes; ionic conductivity increases gradually; and viscosity decreases gradually, indicating that the diffusion resistance of ions decreases. In general, after adding PVDF into the EMITFSI system, the glass-transition temperature and viscosity increase, the ionic conductivity and degree of independent ion motion decrease, and diffusion coefficients of cations decrease faster than those of the anions.

Novel Poly(Vinylidene Fluoride)/Montmorillonite Polymer Inclusion Membrane: Application to Cr(VI) Extraction from Polluted Water

Novel hybrid polymer inclusion membranes (PIMs) based on poly(vinylidene fluoride) (PVDF) (polymer matrix) and Aliquat 336 (ion carrier) and containing native sodium (Cloisite Na⁺ (CNa)) and organo-modified (Cloisite 30B (C30B)) Montmorillonites were elaborated and tested for the removal of toxic Cr(VI) ions from the aqueous solution. The influence of the nanoclay incorporation on the physicochemical properties of PVDF-based PIMs was studied and the resulting membrane transport properties of the Cr(VI) ions were investigated in detail. The water contact angle measurements reveal that the incorporation of the CNa nanofiller affects the membrane wettability as less hydrophilic surface is obtained in this case-~47° in the presence of CNa as compared with ~15° for PIMs with C30B. The membrane rigidity is found to be dependent on the type and size of the used Montmorillonite. The increase of Young's modulus is higher when CNa is incorporated in comparison with C30B. The stiffness of the PIM is strongly increased with CNa amount (four times higher with 30 wt %) which is not the case for C30B (only 1.5 times). Higher Cr(VI) permeation flux is obtained for PIMs containing CNa (~2.7 µmol/(m²·s)) owing to their porous structure as compared with membranes loaded with C30B and those without filler (~2 µmol/(m²·s) in both cases). The PIM with 20 wt % of native sodium Montmorillonite revealed satisfactory stability during five cycles of the Cr(VI) transport due to the high membrane rigidity and hydrophobicity. Much lower macromolecular chain mobility in this case allows limiting the carrier loss, thus increasing the membrane stability. On the contrary, a deterioration of the transport performance is recorded for the membrane filled with C30B and that without filler. The obtained results showed the possibility to extend the PIM lifetime through the incorporation of nanoparticles that diminish the carrier loss (Aliquat 336) from the membrane into the aqueous phase by limiting its mobility within the membrane by tortuosity effect and membrane stiffening without losing its permselective properties.

A Succinct Review on the PVDF/Imidazolium-Based Ionic Liquid Blends and Composites: Preparations, Properties, and Applications

Poly(vinylidene fluoride) (PVDF) is a versatile thermoplastic fluoropolymer with intriguing characteristics, which is receiving considerable attention from researchers in many areas. Recently, PVDF and its copolymer, such as poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) have been blended with ionic liquids to produce blend and composite materials for target applications. In this succinct review, two types of ionic liquids that are utilized for the preparation of PVDF and PVDF-HFP blends and composites, namely, hydrophilic and hydrophobic imidazolium-based ionic liquids, are reviewed. In addition, the effect of the ionic liquids on the physicochemical properties of the PVDF and PVDF-HFP blends and composites, is described as well. On top of that, a multitude of applications of the blends and composites are also succinctly reviewed. This review may give inspirations to the polymer blend and composite researchers in diversifying the applications of thermoplastic fluoropolymers through the utilization of ionic liquids.

Diffusivity and free anion concentration of ionic liquid composite polybenzimidazole membranes

PBI composite membranes containing 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-NTf₂) at 1, 5, 10, 20 and 50 wt% have been prepared and the conductivity has been analyzed by electrochemical impedance spectroscopy.

Using Annealing Treatment on Fabrication Ionic Liquid-Based PVDF Films

In this study, a simple method to obtain pure β-phase directly from the melt process is proposed. A series of PVDF and ionic liquid (IL) was prepared by a solvent casting method with appropriate associated with the subsequent annealing treatment. IL plays a role of filler, which can create strong electrostatic interaction with PVDF matrix and directly induce β-phase crystallization on the PVDF during the melt. PVDF film sample is immersed in hot water for annealing treatment at different temperatures (25 °C to 70 °C). We found that annealing in high temperatures especially can not only increase more IL inserted into the amorphous region of polymer matrix to make more phase transformation, but also accelerate IL removal. Characteristics and performance of the PVDF films were investigated by use of FTIR, XRD, SEM, and AFM. Piezoelectric coefficient d33 as well as d31, degree of crystallinity, and sensitivity are measured in experiment to verify the performance of PVDF film.

Nonbonding interaction analyses on PVDF/[BMIM][BF4] complex system in gas and solution phase

The present study provides a detailed quantum chemical description of the physicochemical interactions between poly-vinylidene fluoride (PVDF) and 1-butyl-3-methyl-imidazolium tetrafluoro borate ([BMIM][BF₄]) ionic liquid (IL). Geometry optimization and frequency calculations are carried out for four monomer units of α- and β-PVDF, [BMIM][BF₄], and PVDF/[BMIM][BF₄] using dispersion corrected density functional theory. The effects of solvation on the systems under study are demonstrated for three polar aprotic solvents, namely tetra-hydrofuran (THF), acetone, and n,n-dimethyl formamide (DMF) using the integral equation formalism polarizable continuum model (IEFPCM). Calculated negative solvation free energy values suggest solution phase stability of the systems under study. Binding and interaction energies for β-PVDF/IL are found higher in magnitude than those for α-PVDF/IL. The nonbonding interaction phenomenon of β-PVDF/[BMIM][BF₄] is elucidated on the basis of natural bond orbital (NBO), Bader's quantum theory of atoms in molecules (QTAIM), delocalization indices, Hirshfeld surface, and reduced density gradient (RDG) analyses. Both anions and cations of ionic liquids are found to show weak van der Waals interaction with PVDF molecule but the anion ([BF₄]^-)/PVDF interaction is found to be stronger than cation ([BMIM]⁺)/PVDF interaction. Inter-unit C-H⋯F type hydrogen bonds are found to show improper (causing blue shifts in vibrational frequencies) nature. Frontier molecular orbital analysis is carried out, and different chemical parameters like electronegativity, chemical potential, chemical hardness and softness, and electrophilicity index are calculated using Koopmans' theorem. Thermochemical calculations are also performed, and the variation in different standard thermodynamic parameters with temperature is formulated. Graphical abstract (a) Hirshfeld surface mapped onto electron density and (b) NCI isosurfaces showing inter-unit interactions of β-PVDF/[BMIM][BF₄].

Investigation on the Crystallization Behaviors of Polyoxymethylene with a Small Amount of Ionic Liquid

Polyoxymethylene (POM) blends with excellent stiffness⁻toughness balance are successfully developed using Tributyl(octyl)phosphonium bis(trifloromethanesulfonyl) imide (TBOP-TFSI), one type of room-temperature ionic liquid, as the nucleating agent. Crystallization behaviors of POM blends have been studied by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The incorporation of TBOP-TFSI induces the crystal nucleation and fine crystal grain of POM, and also a much shorter hemi-crystalline time with only 0.5 wt% addition. The nucleation effect of ionic liquid leads to considerable improvement in the impact strength of POM blends while not sacrificing its tensile strength. Moreover, antistatic properties with a long-time stable performance are achieved by TBOP-TFSI addition as the electrical resistance reaches 1011 Ω/sq.

Hydrophilic Poly(vinylidene Fluoride) Film with Enhanced Inner Channels for Both Water- and Ionic Liquid-Driven Ion-Exchange Polymer Metal Composite Actuators

This study presents a novel and facile strategy to fabricate a hydrophilic poly(vinylidene fluoride) (PVDF) electrolyte film with enhanced inner channels for a high-performance and cost-effective ion-exchange polymer metal composite (IPMC) actuator. The resultant PVDF composite film is composed of hierarchical micro/nanoscale structures: well-defined polymer grains with a diameter of ∼20 μm and much finer particles with a diameter of ∼390 nm, producing three-dimensional interconnected, hierarchical inner channels to facilitate ion migration of IPMC. Interestingly, the electrolyte matrix film has a high porosity of 15.8% and yields a high water uptake of 44.2% and an ionic liquid (IL, [EMIm]·[BF₄]) uptake of 38.1% to make both water-driven and IL-driven IPMC actuators because of the introduction of polar polyvinyl pyrrolidone. Compared to the conventional PVDF/IL-based IPMC, both water-driven and IL-driven PVDF-based IPMCs exhibit high ion migration rates, thus effectively improving the actuation frequency and producing remarkably higher levels of actuation force and displacement. Specifically, the force outputs are increased by 13.4 and 3.0 folds, and the displacement outputs are increased by 2.2 and 1.9 folds. Using an identical electrolyte matrix, water-driven IPMC exhibits stronger electromechanical performance, benefiting to make IPMC actuator with high levels of force and power outputs, whereas IL-driven IPMC exhibits a more stable electromechanical performance, benefiting to make long lifetime IPMC actuator in air. Thus, the resultant IPMCs are promising in the design of artificial muscles with tunable electromechanical performance for flexible actuators or displacement/vibration sensors at low cost.

PVDF based ionogels: applications towards electrochemical devices and membrane separation processes

Ionogels have emerged as one of the most interesting and captivating form of composites which credits to the outstanding characteristics. One of the most important constituent of ionogels is ionic liquid, which show many attractive properties notably non-volatility, in-flammability, negligible vapor pressure, tunability, thermal stability and solvating ability. A large variety of matrix materials have been under consideration for ionogels, presently, polymer/ionic liquid based ionogels have attracted much attention. Numerous polymeric materials such as have been utilized for these polymer/ionic liquids based ionogels. Polyvinylidene fluoride (PVDF) has been on top of the line as a matrix material for polymer based ionogels owing to its stability, aging and chemical resistance and mechanical strength. This review is primarily concerned with the properties of polyvinylidene fluoride based ionogels with an emphasis on their applications in various domains electrochemical devices, gas separation and liquid/liquid separations.

Influence of lithium salt-induced phase separation on thermal behaviors of poly(vinylidene fluoride)/ionic liquid gels and pore/void formation by competition with crystallization

The thermal behavior of poly(vinylidene fluoride)/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide/lithium bis(trifluoromethylsulfonyl)amide (PVDF/[C₂mim][TFSA]/LiTFSA) gels, prepared by cooling from the hot solution, was investigated with various concentrations of LiTFSA (C_LiTFSA). The peak melting temperature (T_m) of the gels shifted toward higher temperatures with increased C_LiTFSA. However, the thickness of lamellar crystal was found to decrease with the increase in C_LiTFSA, which meant that the increase in T_m was not caused by the thickening of lamellar crystal. Furthermore, we found the appearance of domains above T_m in the high C_LiTFSA region (≥20 wt%), which was a lithium ion-rich phase caused by the phase separation. Therefore, it is considered on the basis of Nishi–Wang equation that an increase in the interaction parameter with increasing C_LiTFSA toward the phase separation increased the T_m. The phase-separated domains competed with the subsequent crystallization, which resulted in the formation of micrometer-sized pores and nanometer-sized voids in the spherulites. Spectral measurements revealed that PVDF was not specifically solvated in the solution state above the crystallization temperature, while [TFSA]⁻ anion formed a complex with lithium ion irrespective of the PVDF content. These results led to the consideration that an increase in the interaction parameter might be caused by the strong interaction between lithium ion and [TFSA]⁻ anion to form the complex, which would also lower the interaction between PVDF and [TFSA]⁻ anion.

Lithium salt-induced phase separation on thermal behaviors of PVDF/ionic liquid gels and pore/void structures formation by competition with crystallization.

Physically Cross-Linked Homopolymer Ion Gels for High Performance Electrolyte-Gated Transistors

A new type of physically cross-linked solid polymer electrolyte was demonstrated by using a poly(vinylidene fluoride) (PVDF) homopolymer in a room-temperature ionic liquid. The physical origins of gelation, specific capacitance, ionic conductivity, mechanical property, and capacitive charge modulation in organic thin-film electrochemical transistors were investigated systematically. Gelation occurs through bridging phase-separated homopolymer crystals by polymer chains in the composite electrolyte, thereby forming a rubbery network. The resulting homopolymer ion gels are able to accommodate both outstanding electrical (ionically conductive and capacitive) and mechanical (flexible and free-standing) characteristics of the component ionic liquid and the structuring polymer, respectively. These ion gels were successfully applied to organic thin-film transistors as high-capacitance gate dielectrics. Therefore, these results provide an effective route to generate a highly conductive rubbery polymer electrolyte that can be used in widespread electronic and electrochemical devices.