Systematic Characterization of Degraded Anion Exchange Membranes Retrieved from Vanadium Redox Flow Battery Field Tests.

Commercially available anion exchange membranes were retrieved from VRFB field tests and their degradation due to the various operation conditions is analyzed by in-situ and ex-situ measurements. Ion exchange capacity, permeability and swelling power are used as direct criteria for irreversible changes. Small-angle X-ray scattering (SAXS) and Differential scanning calorimetry (DSC) analyses are used as fingerprint methods and provide information about the morphology and change of the structural properties. A decrease in crystallinity can be detected due to membrane degradation, and, in addition, an indication of reduced polymer chain length is found. While the proton diffusion either increase or decline significantly, the ion exchange capacity and swelling power both are reduced. The observed extent of changes was in good agreement with in-situ measurements in a test cell, where the coulombic and voltage efficiencies are reduced compared to a pristine reference material due to the degradation process.

Nanostructured Thin Films of Moderately Functionalized PMMA-b-PS.

A library of poly(methyl methacrylate)-block-polystyrene (PMMA-b-PS) block copolymers (BCPs) bearing small amounts (<10 mol%) of functional comonomer in either one or both blocks is investigated for their phase separation behavior in bulk and in thin films. Particularly, functionalities typically involved in modern postpolymerization modifications are considered, e.g., azide, pentafluorophenyl, furfuryl. Small-angle X-ray scattering and atomic force microscopy are employed to determine the characteristic dimensional features of lamellae-forming BCPs, which differ essentially in the functional groups. It is shown that the presence of the reactive moieties does not perturb the ability to phase separate in bulk, yet has an impact on the dimensions of the domains. Using a classic two-step procedure involving surface neutralization with a statistical PMMA-co-PS copolymer, it is observed that some functional copolymers are not able to form homogeneous thin films. Solvent stability and crosslinking ability of the films are then briefly assessed as a first step to establishing the functional films as nanoresolved molecular immobilization platform with feature sizes of 20 nm and below.

Single chain self-assembly: preparation of alpha,omega-donor-acceptor chains via living radical polymerization and orthogonal conjugation.

Alpha,omega-hydrogen donor/acceptor functional polymer strands are prepared via a combination of living radical polymerization and orthogonal conjugation and subsequently self-assembled as single chains to emulate--on a simple level--the self-folding behaviour of natural biomacromolecules.

Cationic shape-persistent macrocycles: the unexpected formation of a nano-size supramolecular dimer.

Shape-persistent macrocycles with a rigid pyridyl core and a flexible oligo-alkyl corona aggregate to some extent in nonpolar solvents to form large (tubular) aggregates. To increase the assembling tendency, the intraannular pyridyl groups of the macrocycles were alkylated. Unexpectedly, the quarternized macrocycles show no tendency at all to form tubular micellar-like structures but form well-defined dimers, as determined by X-ray and dynamic light scattering.