FUNCTIONAL POLYMER LABORATORY

The latest polymers are chameleon-like: they change color on deformation. The mechano-chemical transduction mechanism underpinning this effect could be used to make polymers that respond in many other ways to mechanical stress. Our News and Views piece on this subject was published in Nature.

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Upon self-assembly, certain oligo(phenylene vinylene) chromophores exhibit pronounced changes of their optical absorption and/or fluorescence properties. The covalent integration of these dyes into the backbone of polyesters creates new chromogenic pressure-sensitive materials. The work, a collaboration with Prof. David Schiraldi’s group, was selected for the cover of the journal. A US patent that broadly covers this technology has been issued to Case Western Reserve University.

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New stimuli-responsive epoxy coatings with built-in chemical and threshold temperature sensors were developed. The design approach involves incorporating excimer-forming, photoluminescent chromophores into the resin. Color changes resulting from self-assembly or dispersion of dye molecules allow one to monitor exposure of the materials to undesirable external stimuli. A US patent that broadly covers this technology has been issued to Case Western Reserve University.

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The ability to produce polymer nanocomposites, which comprise a percolating, three-dimensional network of well-individualized nanofibers, is important to maximize the reinforcing effect if the nanofibers. Through the utilization of a template–approach, nanocomposites based on an ethylene oxide/epichlorohydrin copolymer and nanofibers isolated from microcrystalline cellulose were produced which display the maximum mechanical reinforcement predicted by the percolation model.

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July 2008: K. D. Singer, J. Lott, T. Kazmierczak, H. Song, Y. Wu, J. Andrews, E. Baer, A. Hiltner, C. Weder; Melt-processed all-polymer distributed Bragg reflector laser; Optics Express 2008, 16, 10358-10363.

Fabricating lasers using polymeric gain media and resonators is attractive due to the relative ease of processing polymers compared to inorganic semiconductors, but manufacturing the microstructures needed has been challenging. In collaboration with Ken Singer’s group of CWRU’s Physics Department and the group of Profs. Eric Baer and Anne Hiltner, we fabricated a surface-emitting distributed Bragg reflector (DBR) laser that has a compression moulded gain medium and a co-extruded resonator. The approach could allow mass production of polymer lasers by rapid roll-to-roll methods.

Increased Electrical Conductivity in Poly(3,4-ethylenedioxythiophene) upon Cross-Linking: The electrical conductivity of poly(3,4-ethylenedioxythiophene) (PEDOT) films can be significantly increased by the incorporation of small amounts of conjugated cross-linkers. Optimized materials display a conductivity of ~800 S/cm; this corresponds to an increase of 36% compared to linear PEDOT. The paper was published as part of Macromolecular Chemistry and Physics series on New Frontiers in Functional Polymers.

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July 2008: K. D. Singer, J. Lott, T. Kazmierczak, H. Song, Y. Wu, J. Andrews, E. Baer, A. Hiltner, C. Weder; Melt-processed all-polymer distributed Bragg reflector laser; Optics Express 2008, 16, 10358-10363.

Fabricating lasers using polymeric gain media and resonators is attractive due to the relative ease of processing polymers compared to inorganic semiconductors, but manufacturing the microstructures needed has been challenging. In collaboration with Ken Singer’s group of CWRU’s Physics Department and the group of Profs. Eric Baer and Anne Hiltner, we fabricated a surface-emitting distributed Bragg reflector (DBR) laser that has a compression moulded gain medium and a co-extruded resonator. The approach could allow mass production of polymer lasers by rapid roll-to-roll methods.

The paper published in one of the world’s most prestigious scholarly scientific journals reports ground-breaking work on a new type of polymer that displays mechanic adaptability. Sea cucumbers have the ability to rapidly alter the stiffness of their dermis. The modulus of this tissue is controlled by regulating the interactions among collagen fibrils, which reinforce a low-modulus matrix. We developed a family of polymer nanocomposites, which mimic this architecture and display similar chemoresponsive mechanic adaptability. Materials based on a rubbery host polymer and rigid cellulose nanofibers exhibit a reversible tensile modulus reduction from 800 to 20 MPa upon exposure to a chemical regulator that mediates nanofiber interactions. Using a host polymer with a thermal transition in the regime of interest, we demonstrated even larger modulus changes (4200 to 1.6 MPa) upon exposure to emulated physiological conditions. Our current focus is the development of “smart” cortical implants based on the new materials. The project is a collaboration with the groups of Profs. Stuart Rowan, Dustin Tyler, and Dr. Jeff Capadona is part of the Advanced Platform Technology (APT) Center at the Louis Stokes Cleveland VA Medical Center.

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New shape memory polymers with built-in temperature sensors were developed by integrating excimer-forming fluorescent chromophores into a cross-linked poly(cyclooctene) matrix. Color changes resulting from self-assembly or dispersion of dye molecules allow one to monitor reaching of the set/release temperature of the materials. The work, a collaboration with Prof. Pat Mather’s group at Syracuse University, was selected for the back cover of the journal and highlighted as a hot paper. A US patent that broadly covers this technology has been issued to Case Western Reserve University.

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For a link to JMCs hot papers click here.

To read a news story on the work click here.

The incorporation of nanoparticles into polymers is a design approach that is employed in all areas of materials science. The concept is attractive since it enables the creation of materials with new or improved properties by mixing multiple constituents and exploiting synergistic effects. The broad technological exploitation of polymer nanocomposites is, however, stifled by the lack of effective methods to control nanoparticle dispersion. Our latest paper reports a simple and versatile process for the formation of homogeneous polymer/nanofiber composites. The approach is based on the formation of a three-dimensional template of well-individualized nanofibers, which is filled with any polymer of choice. We demonstrate that this template approach is broadly applicable and allows for the fabrication of otherwise inaccessible nanocomposites of immiscible components.

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Microporous materials with large specific surface area and pore sizes of molecular dimensions are of interest due to their use in applications that range from selective membranes to molecular sieves to catalysts to photonic crystals. Organic polymers would represent a desirable alternative to inorganic porous materials, since they combine low density with good mechanical properties and ease of processing. However, until recently it was impossible to gain control over their porosity, especially the pore sizes. Several approaches have emerged to solve this problem. Chris Weder’s article in Angewandte Chemie highlights work by Andy Cooper et al., who reported that control over pore size can be achieved in amorphous conjugated poly(arylene ethynylene) networks.

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