Insights into the physics of spray coating of SWNT films

Spray coating is a scalable and high-throughput process for fabrication of transparent and conducting coatings (TCCs) composed of single-walled carbon nanotubes (SWNTs). Presently the fundamentals of this process are not well understood. We show that suppression of coalescence of spray droplets by sufficiently rapid heat- and mass-transfer yields homogeneous SWNT films by preventing the formation of ‘coffee stains’ of larger length scale. Such heat and mass transfer is driven by differential evaporation between the top and edges of the drops, whereas thermal and compositional effects on surface tension and buoyancy are weak. Ultrasonic spraying ensures that the droplets are deposited without significant splashing, and delayed splashing at higher Weber number is evidenced. We find that the performance of spray-coated TCCs made from HiPCO SWNTs is limited by bundle diameter rather than length of the constituent SWNTs and bundes. Vapor acid doping with concentrated sulfuric acid roughly doubles the conductivity of the TCCs.     

High‐Ampacity Power Cables of Tightly‐Packed and Aligned Carbon Nanotubes

The current‐carrying capacity (CCC), or ampacity, of highly‐conductive, light, and strong carbon nanotube (CNT) fibers is characterized by measuring their failure current density (FCD) and continuous current rating (CCR) values. It is shown, both experimentally and theoretically, that the CCC of these fibers is determined by the balance between current‐induced Joule heating and heat exchange with the surroundings. The measured FCD values of the fibers range from 10⁷ to 10⁹ A m^?2 and are generally higher than the previously reported values for aligned buckypapers, carbon fibers, and CNT fibers. To the authors’ knowledge, this is the first time the CCR for a CNT fiber has been reported. The specific CCC value (i.e., normalized by the linear mass density) of these CNT fibers are demonstrated to be higher than those of copper.     

Evaluation of the engineered polysaccharide alpha-1,3 glucan in a thermoplastic polyurethane model system

Enzymatic polymerization is under development as novel scalable process technology to convert sucrose to engineered polysaccharides. Similar to established monomer-based polymerization processes, this approach allows for the synthesis of glucose-based polymers with controlled polymer linkage, structure, and material morphology. Using enzymatic polymerization, alpha-1,3-polyglucose (glucan) can now be produced from sugar on scales required for industrial applications. This alpha-1,3 glucan material, with accessible primary and secondary hydroxyl groups within the overall defined particle morphology, is especially of interest as a partially reactive component in polyurethane chemistry. This study explores the impact of alpha-1,3-glucan as additive in a thermoplastic polyurethane model system and the improvement in mechanical properties of these composites. Glucan was effectively first mixed with a polyether polyol diol, forming a stable dispersion with narrow particle size distribution, followed by reaction with diisocyanate and chain extender to form the polyurethane matrix. The analysis of the generated polyurethane matrix indicates that the hydroxyl groups of the dispersed glucan particles directly react with isocyanate. Tetrahydrofuran solubility of the formed polyurethane compound decreased with the addition of glucan, providing evidence of covalent bonding of glucan leading to cross-linking of the polyurethane matrix. Thermal analysis of this model system suggests that the glucan additive induces hard segment crystallization, resulting in increased hardness and tensile modulus compared with the reference. Based on the observed property enhancements, engineered polysaccharides provide a sustainable performance additive for polyurethane materials.     

Engineered polysaccharide alpha-1,3 glucan as isocyanate-reactive component in viscoelastic polyurethane foams

Enzymatic polymerization is emerging as scalable method to convert sucrose to engineered polysaccharides. Polymer architecture and material properties can be controlled selectively to produce novel differentiated biomaterials. One first example for such an engineered polysaccharide is alpha-1,3-polyglucose (alpha-1,3-glucan) synthesized using glucosyltransferase (GTF) enzymes. Stable dispersions of alpha-1,3-glucan in polyether polyols were prepared with narrow particle size distributions, which are reactive with isocyanate allowing for covalent bonding to the hard segment of the polyurethane polymer matrix. This study further explored the use of alpha-1,3-glucan (PS) in the preparation of viscoelastics (VE) polyurethane foams. The introduction of alpha-1,3-glucan into the polyurethane polymer matrix was found to increase the load-bearing properties of VE foams without impacting the density. Other key performance properties of VE foams were effectively unchanged, including resilience, tensile, and tear strength. Cell size and morphology were also unaffected. The glass transition of these VE foams was not impacted; however, the overall thermal dimensional stability was improved as considerable reduction in compression set was observed. The results of this study indicated that alpha-1,3-glucan disperses in polyether polyols to improve performance characteristics of the VE foams, as well as other flexible polyurethane foams properties.     

Nanotubes as polymers

In this review, we show that the structure and behavior of single-walled nanotubes (SWNTs) are essentially polymeric; in fact, many have referred to SWNTs as “the ultimate polymer”. The classification of SWNTS as polymers is explored by comparing the structure, properties, phase behavior, rheology, processing, and applications of SWNTs with those of rigid-rod polymers. Special attention is given to research efforts focusing on the use of SWNTs as molecular composites (also termed nanocomposites) with SWNTs as the filler and flexible polymer chains as the host. This perspective of “SWNTs as polymers” allows the methods, applications, and theoretical framework of polymer science to be appropriated and applied to nanotubes.