B. Mattsson

Degradation of a fuel cell membrane, as revealed by micro-Raman spectroscopy

We report a micro-Raman spectroscopic study of a fuel cell membrane subjected to fuel cell testing until a significant decline in efficiency was noted. The membrane, poly(vinylidene fluoride)–graft–poly(styrene sulfonic acid), PVDF–g–PSSA, was produced by electron irradiation of a PVDF film, grafting with polystyrene and subsequent sulfonation. Depth profiles show that severe degradation due to loss of polystyrene sulfonic acid has occurred during the fuel cell run. The remaining amount of polystyrene sulfonic acid is of the order of 5–10% of the initial content. Confocal Raman spectroscopy is found to be an excellent tool for investigating the changes in membrane composition after fuel cell experiments.

Phase separation and crystallinity in proton conducting membranes of styrene grafted and sulfonated poly(vinylidene fluoride)

A series of proton exchange membranes have been prepared by the preirradiation grafting method. Styrene was grafted onto a matrix of poly(vinylidene fluoride) (PVDF) after electron beam irradiation. Part of the samples was crosslinked with divinylbenzene (DVB) or bis(vinylphenyl)ethane (BVPE). Subsequent sulfonation gave membranes grafted with poly(styrene sulfonic acid) and marked PVDF-g-PSSA. It was found that the intrinsic crystallinity of the matrix decreased in both the grafting and the sulfonation reaction in all the membranes. The graft penetration and the ion conductivity are influenced strongly by the crosslinker. The ion conductivity is considerably lower in crosslinked membranes than in noncrosslinked ones. Generally, the mechanical strength decreases with crosslinking. The membranes show a regular phase separated structure in which the sulfonated grafts are incorporated in the amorphous parts of the matrix polymer. The phase separated domains are small, of the order of magnitude of 100–250 nm. These were resolved on transmission electron micrographs and on atomic force images but could not be resolved with microprobe Raman spectroscopy.

Ionic configurations in PEO based electrolytes endcapped by CH3-, OH- and SO3-groups

Abstract A Raman scattering study has been carried out on PEO ( MW = 400 − 5 · 10 6 ) with polar (OH-) and non-polar (CH 3- ) end groups, complexed with sodium and lithium triflates. The ionic configurations are determined by observing changes in the SO − 3 , symmetric stretching mode (reflecting anion environment) and metal cation-polyether oxygen modes (reflecting cation-polymer chain coordinations). The results are compared with those of PEO sulfonic acid derivatives (SO 3 -endcapped PEO).

Characterisation of poly(ethylene oxide) sulfonic acids

Abstract PEO sulfonic acids with 〈 M w 〉 in the range 446–4246 have been prepared. Mechanically stable polyelectrolyte films containing high molar mass PEO and PEO sulfonic acids were prepared. The PEO sulfonic acids and the polyelectrolyte films were examined by thermal analysis, optical microscopy, Raman spectroscopy, and impedance spectroscopy. While the low molar mass PEO sulfonic acids were completely amorphous, sulfonic acids with 〈 M w 〉 ≥ 1246 show considerable crystallinity. Experimental data indicate aggregation of the low molar mass PEO sulfonic acids through hydrogen bonds. The PEO sulfonic acids are miscible with high molar mass PEO and form free standing polyelectrolyte films. The PEO sulfonic acids with the lowest molar masses have a plasticizing effect on the high molar mass PEO. The crystallinity of the films decreased as the concentration of sulfonic acid increased. The films are stable at RH ≤ 75%, and for some mixtures protonic conductivities of 10 −3 S cm −1 at room temperature were reached.

A SITE SELECTIVE LUMINESCENCE EXCITATION AND RAMAN SCATTERING STUDY OF EU(CF3SO3)3-PPO ; ION ASSOCIATION AND IONIC EXCHANGE RATE

The luminescence of Eu3+ in a salt–polymer complex, poly(propylene oxide) containing Eu(CF3SO3)3 salt, was studied using broad band and site‐selective excitation. Two distinctly different types of local structure around Eu3+ were detected. To investigate and compare the local structure around the SO3CF−3 anions with that around the Eu3+ cations, a Raman scattering study of the SO3 symmetric stretch vibration was performed in the same system. The vibrational data clearly reveal that also the anions are subject to two types of local environment. It is found that neither of the two states can be attributed to ‘‘free’’ (completely solvated) ions, which implies the existence of two different anion–cation configurations. Temperature and concentration dependent studies of the site‐selective Eu3+ luminescence and the SO3 vibrational spectrum show that the relative amount of ions in the two states is, within the experimental accuracy, constant. However at elevated temperatures there is a rapid exchange between the...

Neutron-scattering studies of a polymer electrolyte, PPO–LiClO4

The structure and dynamics of a prototype polymer electrolyte, PPO–LiClO4, have been investigated using neutron diffraction (ND) and quasi-elastic neutron scattering (QENS). For comparison, corresponding studies of pure PPO have also been performed. The diffraction data reveal large structural changes which are induced by the dopant salt. The phenomena can be explained by local ordering of the chain segments around the solvated cations and by contraction of neighbouring chains via cationic cross links. The QENS results indicate that the segmental motions of the polymer chains, which have been considered to be of vital importance for the ionic mobility, slow down considerably when coordinated to cations. The results are discussed in relation to proposed models for the structure and the conductivity mechanism.

Raman scattering investigations of PEO and PPO sulphonic acids

Abstract Sulphonic acid derivatives of polyethers, of interest as proton conducting materials, were investigated using Raman spectroscopy, focusing on influence of hydration on ion configuration and polymer conformation. Upon increasing hydration we observe a polarised mode building up at approximately 1040 cm −1 , assigned to the symmetric stretching vibration of a completely hydrated SO 3 − group. The data suggest that the proton–sulphonic groups do not dissociate until the materials are considerably hydrated thus explaining the low proton conductivities found for these materials below a relative humidity of 75%.

Spin coated polymer films as hosts for Er3+ with blue and green upconversion radiation

Spin coated polymer films of poly(ethylene oxide) (PEO) containing an Er 3+ salt, ErF 3 , were excited by a red (650 nm) dye laser. Strong green and weaker blue luminescence is observed corresponding to emissions from the thermally coupled 4 S 3/2 and 2 H 11/2 bands and the 2 H 9/2 level, respectively. This is the first time upconversion effects of rare earth ions are reported from a polymeric host.