Eliana Quartarone

Effects of nanoscale SiO2 on the thermal and transport properties of solvent-free, poly(ethylene oxide) (PEO)-based polymer electrolytes

Solvent-free, composite electrolytes based on poly(ethylene oxide) (PEO) have been prepared by using LiClO4 and LiN(CF3SO2)2 as the doping salts, and nanoscale SiO2 as the filler. The samples have been characterized for what concerns their thermal and transport properties. The addition of the filler determines an increase of the conductivity of more than one order-of-magnitude, depending on the filler concentration. The maximum value of 1.4×10−4 ohm−1 cm−1 is obtained for the sample PEO8–LiN(CF3SO2)2–5 wt% SiO2. Effects of the silica thermal history on the conductivity level have been also ascertained. The cation transport number, t+, changes from ~0.1 to ~0.2 when 10 wt% of filler is added.

Effects of water-soluble functionalized multi-walled carbon nanotubes examined by different cytotoxicity methods in human astrocyte D384 and lung A549 cells

The widespread projected use of functionalized carbon nanotubes (CNTs) makes it important to understand their potential harmful effects. Two cell culture systems, human A549 pneumocytes and D384 astrocytoma cells, were used to assess cytotoxicity of multi-walled CNTs (MWCNTs) with varying degrees of functionalization. Laboratory-made highly functionalized hf-MW-NH(2) and less functionalized CNTs (MW-COOH and MW-NH(2)) were tested in comparison with pristine MWCNTs, carbon black (CB) and silica (SiO(2)) by MTT assay and calcein/propidium iodide (PI) staining. Purity and physicochemical properties of the test nanomaterials were also determined. In both MTT and calcein/PI assays, highly functionalized CNTs (hf-MW-NH(2)) caused moderate loss of cell viability at doses >or=100 microg/ml being apparently less cytotoxic than SiO(2). In preparations treated with CB or the other nanotube types (pristine MWCNTs, MW-COOH and the less functionalized amino-substituted MW-NH(2)) the calcein/PI test indicated no loss of cell viability, whereas MTT assay apparently showed apparent cytotoxic response, occurring not dose-dependently at exceedingly low CNT concentrations (1 microg/ml). The latter nanomaterials were difficult to disperse showing higher aggregate ranges and tendency to agglomerate in bundle-like form in cell cultures. In contrast, hf-MW-NH(2) were water soluble and easily dispersible in medium; they presented lower aggregate size range as well as considerably lower length to diameter ratios and low tendency to form aggregates compared to the other CNTs tested. The MTT data may reflect a false positive cytotoxicity signal possibly due to non-specific CNT interaction with cell culture components. Thus, these properties obtained by chemical functionalization, such as water solubility, high dispersibility and low agglomeration tendency were relevant factors in modulating cytotoxicity. This study indicates that properties obtained by chemical functionalization, such as water solubility, high dispersibility and low agglomeration tendency are relevant factors in modulating cytotoxicity of CNTs.

Separation of alkanes and aromatic compounds by packed column gas chromatography using functionalized multi-walled carbon nanotubes as stationary phases.

In the present work, we show a novel application of pristine and functionalized Multi-Walled Carbon Nanotubes (MWCNTs) as stationary phase in low-cost packed columns for the gas chromatographic separation of alkanes and aromatic hydrocarbons. The MWCNTs were deeply investigated by means of physical and chemical methods, like thermal analysis, IR and atomic force microscopy, and Inverse Gas Chromatography (IGC) in order to correlate the adsorption process and surface properties with the material purity level and functionalization degree. The derivatization process of the pristine nanotubes was a key factor to achieve a successful separation of both the light n-alkanes (C3-C5) and the related isomers (C4-C5 branched alkanes). Satisfactory results were similarly obtained in the case of separation of aromatic hydrocarbons (BTX).

Structure and transport properties of polymer gel electrolytes based on PVdf-HFP and LiN(C2F5SO2)2

Abstract Gel polymer electrolytes composed of PVdF/HFP and a non-aqueous lithium electrolyte solution EC/DEC/LiN(C 2 F 5 SO 2 ) 2 (BETI) were prepared to investigate the conduction properties of the gel materials. Structural and micro-structural characterization was carried out by means of modulated differential scanning calorimetry (MDSC) and scanning electron microscopy (SEM). The samples with polymer/solution weight ratios higher than 0.5 contain at least an amorphous swollen gel phase and a crystalline one, while a pure liquid phase appears, which occupies cavities in the micrometer range in the gels with lower polymer content. The transport properties of the gels were investigated by means of impedance spectroscopy for conductivity and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) for diffusion coefficients. The results were compared with those of corresponding films prepared with LiN(CF 3 SO 2 ) 2 (TFSI). The BETI-based samples showed diffusion values lower than the TFSI-based ones. Estimation of the carrier concentration change with the gel composition revealed that the interaction between the host polymer and the electrolyte in the gel especially in the polymer rich region (>50 wt%).

Polymer fuel cells based on polybenzimidazole/H3PO4

Polybenzimidazole-based membranes are nowadays considered the best alternative to Nafion® for the fabrication of high-temperature polymer fuel cells. The rich chemistry of benzimidazole allows us to widely change the physicochemical properties of the resulting polymers and, consequently, to tune the functional properties of the electrolyte membrane. In this perspective we report the most recent developments in PBI-based membranes, cells and stacks. Emphasis is given to problems such as acid leaching, membrane degradation and stack durability.

PVDF-based porous polymer electrolytes for lithium batteries

Abstract Gel electrolytes based on PVDF and PVDF-HFP membranes with different morphology and porosity have been prepared by means of the phase inversion technique. Diffusion coefficients and conductivity have been measured in order to investigate the role of the morphology and microstructure on the dynamics and ionic transport of these multi-phase gels. The picture emerges of a two-steps gelation process, in which the majority of the solution fills up the cavities, while a non-negligible fraction of the salt–solvent mixture swells the amorphous strands of the polymer. Pure PVDF porous membranes display one or two diffusion coefficients, depending on the level of porosity and the film morphology. The two components are attributed respectively (1) to the carriers in the swollen phase and (2) to the pure solution, whose motion can be “free” or, in such cases, partially restricted by the barriers of the cavities. A single component can be interpreted as a sort of average between the pure solution and the swollen phase. PVDF-HFP membranes generally present two diffusion coefficients and show an opposite behaviour between the cation and anion species, concerning their relative amounts.

Investigations by impedance spectroscopy on the behaviour of poly(N,N-dimethylpropargylamine) as humidity sensor

Abstract A thin film of poly( N , N -dimethylpropargylamine) (PDMPA), deposited by spin coating over a SiO 2 substrate covered by an interdigitated array of chromium electrodes, was characterised by impedance spectroscopy at different relative humidity levels, ranging from ∼0 to ∼90% relative humidity (RH). The logarithm of the film conductance exhibits a linear behaviour from very low RH contents up to more than 70% RH. The dynamic range of the variation of the conductance is extremely high (∼6 orders-of-magnitude) and it allows a promising use of the film as a humidity sensor.

A photocatalytic water splitting device for separate hydrogen and oxygen evolution.

A two-compartment Plexiglas cell has been set up and tested for separate hydrogen and oxygen production from photocatalytic water splitting on a thin TiO2 layer deposited by magnetron sputtering on a flat Ti electrode inserted between the two cell compartments.

Transport and thermal properties of (PEO)n–LiPF6 electrolytes for super-ambient applications

Abstract Poly(ethylene oxide) (PEO)-based solvent-free electrolytes may be used for applications above room temperature, e.g. in batteries for electric vehicles. The system PEO–LiPF 6 has to date received only scarce attention because of the poor thermal stability and hygroscopicity of the lithium salt. However, for applications above the melting of PEO crystalline phase, it is possible to consider films with relatively low salt content, which can overcome the above-mentioned problem. In this paper, we perform a thermal and transport characterisation of the system PEO–LiPF 6 . We show that conductivity values above 10 −4 Ω −1 cm −1 can be reached at 70°C for n =EO/Li=30. The addition of nanoscale silica is shown to influence the thermal decomposition of the salt.

Long-term structural stability of PMMA-based gel polymer electrolytes

Abstract Gel-based SPEs are promising candidates as polymer electrolytes in electrochemical devices such as Li-ion batteries. In particular, PMMA-based gel electrolytes have shown electrical conductivity at room temperature as high as 10 −3 Scm −1 . One of the most important drawbacks of these gels is their lack of long-term structural stability, which determines a reduction of the contact area with the electrode and causes drops in conductance. We have observed macroscopic volume reductions (>5%) in gels made of PMMA, ethylene carbonate (EC), dimethyl carbonate (DMC) and LiN(CF 3 SO 2 ) 2 . The timescale of this phenomenon depends on the ratio EC/DMC. In this paper we investigate the structural modifications induced in the above mentioned system by annealing for several months at room temperature. We show that a crystalline phase grows in a matter of weeks with a kinetics controlled by the ratio EC/DMC and disappears for longer annealings.