K. Jokela

The state of water and the nature of ion clustersin crosslinked proton conducting membranes of styrene grafted and sulfonatedpoly(vinylidene fluoride)

Proton conducting membranes were prepared by irradiation grafting with styrene followed by sulfonation on matrices of poly(vinylidene fluoride), PVDF. Membranes crosslinked with divinylbenzene and/or bis(vinylphenyl)ethane were compared to non-crosslinked membranes. The ion conductivity of the crosslinked membranes is lower than that of the non-crosslinked membranes. This is due partly to the very inefficient sulfonation of the crosslinked membranes below the graft penetration level, which in turn leads to a low water uptake at low degrees of grafting. The graft penetration level is lower in crosslinked membranes than in non-crosslinked membranes. This leads to a more compact structure of the crosslinked grafts within the matrix. The lower ion conductivity in the crosslinked membranes is therefore partly also due to restricted mobility of the ion clusters necessary for ion and water transport in the membranes.

Effects of a fuel cell test on the structure of irradiation grafted ion exchange membranes based on different fluoropolymers

The role of the fluoropolymer matrix in the stability of irradiation grafted proton conducting membranes under fuel cell conditions is investigated. The structure of a series of membranes with poly(vinylidene fluoride), poly(vinylidene fluoride-co-hexafluoropropylene), poly(tetrafluoroethylene-co-hexafluoropropylene), and poly(ethylene-alt-tetrafluoroethylene) matrices with poly(styrene sulfonic acid) side chains is studied before and after a fuel cell test using X-ray scattering techniques and confocal micro-Raman spectroscopy. All tested membranes suffer from a loss of poly(styrene sulfonic acid) leading to a decrease in conductivity. Changes in crystallinity, lamellar period, orientation and thickness of the membranes are reported and compared to corresponding properties of the initial polymer films and the pristine membranes. The membranes where most severe changes in the structure of the matrix polymer can be observed have the shortest lifetimes in the fuel cell.

Polarized luminescence from self-assembled, aligned, and cleaved supramolecules of highly ordered rodlike polymers

A hierarchical self-assembly in comb-shaped supramolecules of conjugated rodlike polymers is reported. The supramolecules consist of poly(2,5-pyridinediyl), acid dopants, and hydrogen bonded alkyl side chains. A thermotropic smectic state with an exceptionally large coherence length is formed without additional solvent. This allows facile overall alignment resulting in high dichroism and polarized photoluminescence. Solid films are formed by cleaving side groups from the supramolecules which retain the optical anisotropy together with the high photoluminescence quantum yield of pristine polymer.

Self-Organized Liquid Phase and Co-Crystallization of Rod-Like Polymers Hydrogen-Bonded to Amphiphilic Molecules**

Application to rod-likepolymers (such as p-conjugated electroactive polymers)could lead to possible new applications, but is not straight-forward because such polymers tend to be infusible andpoorly soluble. For polymers containing rod-like moieties,self-organization has been achieved based on di-block co-polymers with flexible blocks,

Structure of Sulfonated poly(vinyl fluoride)

Sulfonated poly(vinyl fluoride) (PVF-SA) has been made by chemical sulfonation or radiation-induced sulfonation of commercial poly(vinyl fluoride) (PVF) films. The effects of the irradiation treatment and sulfonation on sulfonic acid distribution, crystallinity, state of water, and molecular organization have been examined. The results indicate that proton irradiation and subsequent sulfonation produce a structure that is different from the ones produced by the sulfonation of nonirradiated or electron beam (EB)-irradiated samples. The water uptake is higher in proton-irradiated samples than in the other samples. In addition, the portion of nonfreezing water is highest in proton-irradiated samples. Infrared spectra of the sulfonated samples indicate that a large part of the freezing bound water is associated with the hydrophobic polymer backbone. However, this portion was smaller in the proton-irradiated sample than in the EB-irradiated sample. The proton-irradiated samples had a small-angle X-ray diffraction maximum with a corresponding Bragg spacing of 70 A, which was taken as evidence for the formation of ion–water cluster domains in the proton-irradiated samples. The ion conductivity was slightly lower in nonirradiated and in EB-irradiated membranes than in the proton-irradiated sulfonated samples in which the highest values were 10–20 mS/cm.

ASAXS study of styrene-grafted sulfonated poly(vinylidene fluoride) membranes

Small-angle and wide-angle X-ray scattering and anomalous small-angle X-ray scattering were used to investigate proton-conducting membranes prepared by radiation-induced styrene grafting and sulfonation of commercial poly(vinylidene fluoride) (PVDF-g-PS) films. The membranes retain the lamellar and highly oriented structure of the original PVDF films even through excessive grafting and sulfonation. The sulfonate groups aggregate in the central part of the amorphous layers, where they form a weakly ordered structure that does not show any preferred orientation. This structure is suggested to be lamellar with alternate metal-sulfonated hydrate and PVDF-g-PS layers. The lamellar period is 15.1 A.

Diffraction analysis of highly ordered smectic supramolecules of conjugated rodlike polymers

A small/wide-angle X-ray scattering and grazing incidence diffraction study of comb-shaped supramolecules of conjugated poly(2,5-pyridinediyl), acid dopant and hydrogen bonded amphiphilic side chains is reported. In solution, polymers are dissolved rodlike particles. When the side-chains are introduced, polymers self-assemble in hierarchic liquid crystals (LC). Diffraction patterns of aligned LC show h00, 020, and 004 reflections, and additional small-angle reflections along the polymer axis. A triangular correlation function indicating a very large correlation length is seen along the smectic axis. An aligned solid structure can be formed by cleaving side chains from the aligned LC.

SAXS studies on Kynar-based membranes for fuel cells

The structure of the styrene grafted and sulfonated poly(vinylidenefluoride-co-hexafluoropropylene) was studied by small angle x-ray scattering, SAXS. The starting material is lamellar and the grafting and sulfonation processes and the hexafluoropropylene, HFP, contents affected the lamellar period. The SAXS intensity curve of the sulfonated membranes also included an ionic peak which arises from the ionic aggregates. The effects of the humidy and metal ion neutralization on the ionic aggregates were studied.

Self-Assembled, Aligned, and Cleaved Supramolecules of Poly(2,5-pyridinediyl)

We report on directed self-assembly in supramolecules containing rod-like polymers. The comb-shaped supramolecules consist of poly(2,5-pyridinediyl), camphorsulfonic acid, and hydrogen bonded amphiphilic side chains. Locally they form highly ordered lamellar structures in which the polymers are stacked. The liquid crystalline state allows facile overall alignment yielding absorption dichroism and polarized photoluminescence. After alignment, cleavage of the amphiphiles results in solid films which retain this optical anisotropy with the high photoluminescence quantum yield.