From fundamental science to advanced technologies (2013)

Situated at the crossroads between fundamental and applied science, polymer physics remains a vibrant field in which discovering new properties of, and fabrication strategies for, macromolecules with important practical consequences is key. Basic advances in our understanding of the molecular-level structure of polymers continue to reveal key structure-property relationships in “old” materials, while enabling the development of new materials that exhibit previously inconceivable combinations of properties. Thus, polymer physics informs the design, synthesis, and processing of polymers for electrical energy storage and utilization, the directed self-assembly of copolymers at nanometer length-scales, the bottom-up development of new materials based on insights into chain motion in single polymer systems and in polymer glasses, the investigation of bio-inspired and biologically relevant materials that promote human health, and the fabrication of “smart” nanocomposites with unusual strength. This special issue highlights new work in each of these areas from the next generation of polymer physicists. Several young researchers are employing their unique insights into molecular design and nanostructure manipulation to meet pressing needs for new materials for electrical energy storage and utilization. In this issue, Park and Kim outline key physical principles that define the structure-ionic conductivity relationships in sulfonated polymers, which will guide the de novo design of new high temperature polymer electrolyte membranes. Mike and Lutkenhaus focus on recent advances in conjugated polymers for energy storage applications, including the synthesis and processing of materials such as polyaniline, for flexible, cost-effective, and lightweight electrode materials. In a complementary article, Salleo and co-workers report on the role of monolayer surfaces in directing the crystallization of poly(3-hexylthiophene) [P3HT] to improve its carrier mobility in field-effect devices. Directed assembly of block copolymer thin films provides access to nanoscale templates for high-density magnetic storage media, topographic arrays, and nanoporous separations membranes. Rational template design requires insight into the roles of film thickness, interfacial interactions, and polymer segregation strength on copolymer ordering, as described by Ryu and co-workers. Meanwhile, Stein and co-workers expand on these efforts and describe a simple and rapid, yet robust, method for quantifying copolymer domain orientations and defects in cylindrical and lamellar block copolymer thin films using X-ray scattering. Ellison and co-workers describe the use of convective flows for thin film patterning, a complementary method for directed self-assembly that facilitates photochemical approaches to multilayer films. Confining polymer chains in various microenvironments provides new insights into polymer dynamics. Marciel and Schroeder provide a molecular-level understanding of the static and dynamic solution properties of single polymer chains obtained from single molecule spectroscopies, with an emphasis on the new avenues of investigation enabled by these methods. On the other hand, geometrically confining glassy polymers unexpectedly alters their thermal and mechanical properties. Priestley and co-workers describe advances in molecular deposition techniques for fabricating confined glassy polymers and highlight some of these materials' surprising properties. Biologically inspired materials with unusual structures and dynamics present exciting opportunities to develop “smart” materials that adapt and respond to environmental cues. Olsen and co-workers outline studies of engineered peptides that form “perfect” polymer networks for detailed rheological studies, while also leading to bio-functional and bio-responsive hydrogels for human health applications. Zhang and Li highlight the design of synthetic peptide-based copolymers that display stimuli-responsive changes in their primary and secondary structures, while Savin and co-workers describe the dynamic interplay of chain connectivity and peptide secondary structure in driving the formation of unique polymer morphologies under variable solution conditions. Wanasekara and Korley detail polymer processing methods that generate bio-inspired and self-assembled materials with adaptive mechanical properties. These nanocomposite systems address key aspects of tailored interfacial adhesion and controlled dispersion, two fundamental research parameters in multi-component and nanoscale materials. In a related vein, Jayaraman summarizes recent theoretical and simulation insights into the behavior of polymer-grafted nanoparticles in a polymer matrix. This work provides guiding principles for the manipulation of nanocomposite morphology as a function of polymer chemistry and molecular weight (and molecular weight dispersity), as well as particle grafting density. Finally, Bang and co-workers present a complementary discussion of recent experimental strategies for the generation of thermally stable nanoparticle surfaces for incorporation into nanoparticle arrays. The approaches described in this work obviate difficulties associated with nanoparticle/ligand instability under the heat treatments typically employed in polymer/nanocomposite fabrication. In the face of pressing societal needs for new and sustainable technologies, these young investigators clearly demonstrate that fundamental polymer physics continues to contribute deep physical insights into the unusual properties of macromolecular materials. These discoveries furnish a firm foundation for the development of innovative and disruptive soft materials technologies.