A. Brodin

Molecular and ionic interactions in poly(acrylonitrile)- and poly(methylmetacrylate)-based gel electrolytes

Vibrational Raman and Fourier transform IR (FTIR) spectroscopy has been used to determine molecular and ionic interactions in poly(acrylonitrile)—(PAN) and poly(methylmetacrylate)—(PMMA) based gel electrolytes, containing LiClO4 salt and a mixture of ethylene carbonate (EC) and propylene carbonate (PC) as a gelating agent. A number of model systems, representing different stages of gel preparation, as well as the pure components, have also been studied. Vibrational spectra reveal interactions between EC and PC molecules in EC–PC mixture via electric dipoles located on C=O groups. In the salt-doped EC–PC system, additional bands close to the ring breathing and bending fundamentals of the carbonate ring of EC and PC, respectively, are attributed to solvent molecules interacting with the cations via Coulombic forces, the satellite band frequencies being well correlated to the cationic potentials. In the PMMA-based gels, no spectroscopically detectable interactions between the polymer matrix and the electroly...

Poly(methyl methacrylate)-based protonic gel electrolytes: a spectroscopic study

We present the first vibrational spectroscopic investigation of a novel non-aqeous proton conducting polymer gel electrolyte consisting of a PMMA matrix and a solvent mixture (ethylene carbonate (EC)/propylene carbonate (PC) or EC/PC/-N,Ndimethylformamide (DMF)) with a dissolved organic acid (benzoic or salicylic acid). The protonic conductivity of the gels is of the order ∼ 10 -4 - 10 -5 S/cm at room temperature. We show that the conductivity is proportional to the degree of dissociation of the acid, the latter determined from Raman spectroscopic data, and that the degree of dissociation depends on the properties of the solvent mixture. Finally, we comment on the relation between the proton conductivity and the solvent diffusion dynamics as studied by PCS.

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).

Relaxational and vibrational dynamics of poly(propylene glycol)

Abstract Photon correlation spectroscopy has been used to study structural relaxation dynamics near the glass transition temperature for glass-forming linear chain molecules differing in the number of repeat units. Complementary investigations of the low-frequency vibrational dynamics were performed by means of Raman spectroscopy. The systems studied range from the low molecular weight liquid propylene glycol (PG, molecular weight (MW)=76) to the polymer, poly(propyleneglycol) (PPG, MW=4000). Differences are observed in terms of the fragility of the systems. The findings are attributed to bonding between the hydroxy endgroups which decrease in density as the MW increases.

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...

Raman study of water in Nafion-117 membranes

Abstract We report on a Raman scattering study of the state of water in the acid form of the perfluorosulfonate exchanger membrane Nafion-117 in H 2 O- and D 2 O-wet conditions. The data reveal that in Nafion-117 (molecular weight 1100), as distinct from Nafion with higher molecular weights (1200 and 1400), practically all water molecules participate in OH · · · H bonding rather than linking to the fluorocarbon matrix. Moreover, the shifts of the OH and OD bands in Nafion-1100 towards higher frequencies as compared to Nafion of larger equivalent weights (1200 and 1400) implies that the state of water in Nafion-117 is more bulk-like than in the higher molecular weight membranes.

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.

Quasi-elastic Raman scattering and free volume in isotropic pressure-densified atactic poly(methyl methacrylate) glasses

We have made a series of isotropic pressure-densified atactic poly(methyl methacrylate) (PMMA) glasses with densities ranging from 1.1823 g/cm3 to 1.1963 g/cm3, in order to investigate how the glassy dynamics, measured by Raman scattering in the frequency range of 0.1–10 THz, depends on the thermomechanical history of the glasses. In particular, we investigate whether there is a correlation between the strength of the fast relaxation dynamics and the free-volume characteristics, such as the average free-volume size and the free-volume fraction. The fast relaxation strength is deduced from the quasielastic light scattering (QES) intensity; the free-volume size is measured with positron annihilation lifetime spectroscopy (PALS); and the free-volume fraction is determined from pressure–volume–temperature (PVT) data and the Simha–Somcynsky equation-of-state (EOS) theory. Our temperature-dependent Raman and PALS measurements show that both the QES intensity and the ortho-positronium (o-Ps) lifetime increase sm...

Low-frequency vibrations in monomers, dimers and polymers of propylene glycol

Abstract We have studied the low-frequency dynamics of oligomers (n = 1 and n = 2) and polymers (n = 45) of propylene glycol using molecular dynamics (MD) simulations. The polymer structure was built from a reverse Monte Carlo (RMC) simulation of the static structure factors S(Q) obtained for ordinary and deuterated poly(prolylene oxide) from neutron diffraction. The fraction of the different stereo-isomers obtained in this way was checked by performing 13C nuclear magnetic resonance studies on the polymers. The RMC polymer structure was used as a starting structure for MD simulations of the polymer, whereas the shorter-chain oligomers were simulated using random starting structures. The vibrational density of states was calculated from the Fourier transform of the velocity autocorrelation function. Our results indicate that the low-frequency peak below 100 cm−1, generally referred to as the boson peak, is to a large extent due to intermolecular degrees of freedom, the peak position and shape being rather...