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Bioinspired gradient materials via blending of polymer electrolytes and applying electric forces.

ABSTRACT: Free-standing and supported films with a lateral gradient in composition were prepared using blends of poly(acrylic acid) (PAA)/sodium salt and its copolymers with acrylamide (AAm) in an applied electric field. The gradients were stabilized by complexation of carboxylate groups with metal species. To find the favorable conditions and components for successful blending and interaction with Fe and Ce species, we studied blending of the two PAA samples with molecular weights of 2000 and 15 000 Da with two copolymers of AA and AAm (with 10 and 70 wt % of AA units) and interaction of these blends with Fe(III) and Ce(IV) ions. The structure of the hybrid (blend) films was studied using differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, X-ray diffraction, and optical microscopy. To ensure blend miscibility and efficient interaction with metal ions, the copolymer containing 70 wt % AA units has been used. The surface enrichment with metal species was observed at all experimental conditions studied in this work. For lateral gradient film formation, 15 000 Da PAA has been used to avoid uneven distribution of the homopolymer in the film, observed for 2000 Da PAA. The gradient films were characterized by XPS. The lateral gradient of functionality such as COONa group or Fe content has been obtained at different strengths of electric field applied during film formation. The use of lower voltage allows one to prevent NaOH formation and creates more favorable conditions for development of a gradient polymer film. The Ce content gradient was not observed due to formation of large Ce oxide particles (> or = 750 nm), masking the gradient of functionality. For the first time, free-standing films with a lateral gradient in composition were prepared using an applied electric field.

SUBMITTER: Bronstein LM

PROVIDER: S-EPMC2630488 | biostudies-literature | 2009 Jan

REPOSITORIES: biostudies-literature

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Bioinspired gradient materials via blending of polymer electrolytes and applying electric forces.

Bronstein Lyudmila M LM Ivanovskaya Anna A Mates Tom T Holten-Andersen Niels N Stucky Galen D GD

The journal of physical chemistry. B 20090101 3

Free-standing and supported films with a lateral gradient in composition were prepared using blends of poly(acrylic acid) (PAA)/sodium salt and its copolymers with acrylamide (AAm) in an applied electric field. The gradients were stabilized by complexation of carboxylate groups with metal species. To find the favorable conditions and components for successful blending and interaction with Fe and Ce species, we studied blending of the two PAA samples with molecular weights of 2000 and 15 000 Da w ...[more]

PMID: 19105643

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Project description:The optimization of ionic conductivity and lithium-ion battery stability can be achieved by independently tuning the ion transport and mechanical robustness of block polymer (BP) electrolytes. However, the ionic conductivity of BP electrolytes is inherently limited by the covalent attachment of the ionically conductive block to the mechanically robust block, among other factors. Herein, the BP electrolyte polystyrene-block-poly(oligo-oxyethylene methacrylate) [PS-b-POEM] was blended with POEM homopolymers of varying molecular weights. The incorporation of a higher molecular weight homopolymer additive (α > 1 state) promoted a "dry brush-like" homopolymer distribution within the BP self-assembly and led to higher lithium salt concentrations in the more mobile homopolymer-rich region, increasing overall ionic conductivity relative to the "wet brush-like" (α < 1 state) and unblended composites, where α is the molecular weight ratio between the POEM homopolymer and the POEM block in the copolymer. Neutron and X-ray reflectometry (NR and XRR, respectively) provided additional details on the lithium salt and polymer distributions. From XRR, the α > 1 blends showed increased interfacial widths in comparison to their BP (unblended) or α < 1 counterparts because of the more central distribution of the homopolymer. This result, paired with NR data that suggested even salt concentrations across the POEM domains, implied that there was a higher salt concentration in the homopolymer POEM-rich regions in the dry brush blend than in the wet brush blend. Furthermore, using 7Li solid-state nuclear magnetic resonance spectroscopy, we found a temperature corresponding to a transition in lithium mobility (TLi mobility) that was a function of blend type. TLi mobility was found to be 39 °C above Tg in all cases. Interestingly, the ionic conductivity of the blended BPs was highest in the α > 1 composites, even though these composites had higher Tgs than the α < 1 composites, demonstrating that homopolymer-rich conducting pathways formed in the α > 1 assemblies had a larger influence on conductivity than the greater lithium ion mobility in the α < 1 blends.

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Bioinspired gradient materials via blending of polymer electrolytes and applying electric forces.

Publications

Bioinspired gradient materials via blending of polymer electrolytes and applying electric forces.

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