Jan Lindgren

Crystallinity and morphology of PVdF-HFP based gel electrolytes.

Abstract The structural behaviour of a random copolymer consisting of polyvinylidene fluoride (PVdF) and hexafluoropropylene (HFP), when mixed with organic solvents and a lithium salt, has been investigated. In its neat form, the copolymer exhibits a semicrystalline matrix, where the PVdF constituent crystallises partially. The crystalline phase appears mostly as the non-polar (trans–gauche–trans–gauche′) phase II. The relative crystallinity of the PVdF domains remains constant on addition of a plasticiser, propylene carbonate (PC) or triethylene glycol dimethyl ether (TG), but is greatly decreased on addition of the salts lithium bis(trifluoromethane sulfone) imide, Li(TFSI) or lithium tetrafluoroborate, LiBF4. This is shown by the results from both wide-angle (WAXS) and small-angle (SAXS) X-ray scattering and FTIR-spectroscopy. Surprisingly, the addition of such a polar medium as the salt, and to a lesser extent the plasticisers, also causes a change in the structure of the crystalline phase to a more polar phase III (intermediate polar conformation). The thermal stability of the gels and the large influence the salt addition has on the material is also shown by the results from differential scanning calorimetry (DSC) measurements.

FTIR study of water in cast Nafion films

The state of water in cast perfluorosulphonic Nafion films has been investigated using Fourier transform infrared spectroscopy (FTIR). FTIR spectra of cast Nafion films equilibrated in different relative humidities (RH) in a non flowing vapour environment, and in 100% RH at different temperatures have been made. In contrast to previously published results on thicker membranes the FTIR experiments indicate that there is already a full proton transfer from the sulphonic acid group in Nafion when there is one water molecule per sulphonate group.

Degradation mechanisms in a dye-sensitized solar cell studied by UV–VIS and IR spectroscopy

By deliberately causing degradation of components in a dye-sensitized solar cell we have studied failure mechanisms of such cells. The dye, bis(tetrabutylammonium) cis–bis(thiocyanato)bis(2,2′-bipy ...

On the correlation between deuteron quadrupole coupling constants, O-H and O-D stretching frequencies and hydrogen-bond distances in solid hydrates

Abstract Correlation curves are reported relating deuteron quadrupole coupling constants ( e 2 qQ/h ) to O-H and O-D stretching frequencies ( v OH and v OD ) for isotopically-dilute HDO molecules. Correlation curves are also given relating these quantities to hydrogen-bond distances. The best correlations are found to be between ( e 2 qQ/h ) and v OH and v OD whereas the correlations involving intermolecular geometries show considerably greater scatter. Complications caused by the effects of anharmonicity on the stretching vibrations and of vibrational averaging of the quadrupole coupling and geometrical parameters are discussed in light of the observed correlations. It is concluded that, although these effects are large, their magnitude is also strongly correlated with the stretching frequencies, quadrupole couplings and geometrical parameters.

Protection mechanism of Tween 80 during freeze-thawing of a model protein, LDH.

The purpose of the study was to investigate the protective mechanism of a non-ionic surfactant, Tween 80, at freeze-thawing with controlled temperature history of a model protein, lactate dehydrogenase (LDH). The system was examined by differential scanning calorimetry (DSC) and infrared spectroscopy (IR). LDH activity assays were performed spectrophotometrically. In all samples, independent of temperature history and addition of surfactant, all water was crystallized to polycrystalline ice at temperatures below -20 degrees C. The size and perfection of the ice crystals could be varied by a range of cooling rates giving different degrees of undercooling. At Tween concentrations below the cmc at crystallization, lower concentrations were required at low cooling rates compared to higher cooling rates to protect LDH. Concentrations above cmc of Tween reduced the protection at a cooling rate of 5 degrees C min(-1) and at quenching in N(2)(l). The amount of Tween needed for complete protection correlated to the surface area of the ice crystals at a certain temperature history. Tween 80 protects LDH from denaturation at freeze-thawing by hindering its destructive interaction with the ice crystals. The protective effect might be obtained when Tween molecules compete with the protein for sites on the ice surface. The optimum concentration of Tween needed for complete protection is dependent on the temperature history.

Coordination and conformation in PEO, PEGM and PEG systems containing lithium or lanthanum triflate

The effect of chain length, cation type and polymer end group on the coordination and conformation in polymer electrolytes has been studied using high molecular weight poly(ethylene oxide) (PEO), poly(ethylene glycol) (PEG(400)) and poly(ethylene glycol)dimethyl ether (PEGM(400)) as polymers, with LiCF3SO3 and La(CF3SO3)3 as salts. The experimental technique used has been Fourier transform infra-red spectroscopy. A coordination of nine to ten ether oxygens to the lanthanum ions has been found for the PEGM system by increasing the concentration of lanthanum triflate in the polymers and following the disappearance of the COC stretching vibration of non-coordinated ether oxygens. The same coordination seems to be present also for the PEG and PEO systems. Conformational changes have been observed on addition of salt to the polymer, by following the disappearance of an absorption band at about 990 cm−1, indicative of a trans conformation around the CH2CH2 bond. For all three polymer types the gauche conformation is dominant at high salt concentrations. The OH end groups present in the PEG samples are important for the coordination in this system and both the cations and the triflate anions are coordinated by the OH groups to some extent.

O-H and O-D stretching vibrations in isotopically dilute HDO molecules in some solid hydrates

Abstract Vibrational frequencies vOH and vOD have been measured for isotopically-dilute HDO molecules in eleven solid hydrates at 90 K. The results have been used to prepare a plot of the ratio vOH/vOD versus vOH. The ratios fall on a smooth curve and decrease with decreasing frequencies vOH. The anharmonicity constants ωexe have been estimated. They were found to increase with decreasing vOH.

Contact ion pair formation and ether oxygen coordination in the polymer electrolytes M[N(CF3SO2)2]2PEOn for M = Mg, Ca, Sr and Ba

The polymer electrolytes M[N(CF3SO2)2]2PEOn for M = Mg, Ca, Sr and Ba have been investigated using infra-red spectroscopy, differential scanning calorimetry and impedance spectroscopy. The effects of varying concentration (n = 6–40) and temperature (25–95°C) on the contact ion pair formation and cation coordination have been studied. Contact ion pairs are only found for the most concentrated samples (n < 9). Ion pairs occur with two types of structures: one type is found for samples containing Mg2+ and the other for samples with Ca2+, Sr2+ and Ba2+. The conductivities of the samples are discussed in terms of radii and coordination numbers of the cations.

Ion aggregation and morphology for poly (ethylene oxide)-based polymer electrolytes containing rare earth metal salts

Abstract Polymers containing rare earth metal salts are potentially interesting laser materials, where it is most important that the materials should have good optical quality. In this connection, comparative studies of the relationship between ion pair/clustering formation and cation-PEO coordination have been made for the system Ln(CF3SO3)3PEOn for different concentrations and temperatures, where Ln = La, Nd, Eu, Dy and Yb and n = 9, 16 and 24. The v(COC) modes in PEO and the v(SO3) modes in the CF3SO−3 ion have been monitored using FTIR spectroscopy. All samples were totally amorphous for n = 9 and 16, while a mixture of crystalline PEO and an amorphous phase was obtained for n = 24. Different ion aggregates (pairs/clusters) involving cations and the triflate ions have been observed, as evidenced by splittings and shifts in the symmetric and the antisymmetric SO3 stretching bands. Shifts in the v(COC) modes indicate bonding between cations and ether oxygens. The spectra at any given concentration and temperature are almost identical for all rare earth metals studied except ytterbium, suggesting an isomorphous structure.

Model calculations of the vibrations of bonded water molecules

Abstract Model calculations have been made of the vibrational frequencies and normal modes of a water molecule vibrating in a combined internal and external field. A constant internal force field has been used together with an external central force field from four or three nearest-neighbour atoms to the water molecule. These neighbour atoms have been arranged either tetrahedrally or trigonally around the water molecule. The external force field has been further restricted by the use of five possible site symmetries for the water molecule, C 2v , C 2 , C s (σ xz , C s (σ yz ) and C 1 . A series of calculations have been made where the external force constants have been varied within the range 1—80 Nm −1 . The nine calculated normal modes can be divided into three groups: intra-molecular, rotational and translational vibrations. Among the rotational vibrations it is found that, in the tetrahedral environment, the rocking mode occurs at lower frequencies than the twisting and wagging modes, whereas the opposite occurs for the trigonal environment. Frequency ratios have been calculated using the isotopic species H 2 O, D 2 O, HDO and H, 18 O. The twisting and wagging modes have the v H 2 O/ v D 2 O ratio in the range 1.35-3-1.41 and the rocking mode in the range 1.26—1.41.