Chemical and Physical Drivers for Improvement in Permeance and Stability of Linker-Free Graphene Oxide Membranes.

Graphene oxide (GO) is a promising membrane material for chemical separations, including water treatment. However, GO has often required postsynthesis chemical modifications, such as linkers or intercalants, to improve either the permeability, performance, or mechanical integrity of GO membranes. In this work, we explore two different feedstocks of GO to investigate chemical and physical differences, where we observe up to a 100× discrepancy in the permeability-mass loading trade-off while maintaining nanofiltration capacity. GO membranes also show structural stability and chemical resilience to harsh pH conditions and bleach treatment. We probe GO and the resulting assembled membranes through a variety of characterization approaches, including a novel scanning-transmission-electron-microscopy-based visualization approach, to connect differences in sheet stacking and oxide functional groups to significant improvements in permeability and chemical stability.

Natural Carbon By-Products for Transparent Heaters: The Case of Steam-Cracker Tar.

Steam-cracker tar (SCT) is a by-product of ethylene production that is in massive quantities globally (>150 × 106 tons per year). With few useful applications, the production of unwanted SCT leads to the need for its costly disposal or burning at the boiler plant. The discovery of new uses for SCT would therefore bring both economic and environmental benefits, although, to date, efforts toward employing SCT in diverse applications have been limited, and progress is further hampered by a lack of understanding of the material itself. Although complex and highly heterogeneous in nature, the molecular composition of SCT has the potential to serve as a diverse and tunable feedstock for wide-ranging applications. Here, a simple solution-processing method for SCT that allows its conductivity and optical properties to be controlled over orders of magnitude is reported. Here, by way of example, the focus is on the production of transparent conductive thin films, which exhibit a wide range of transparencies (23-93%) and sheet resistances (2.5 Ω â–¡-1 to 1.2 kΩ â–¡-1 ) that are tuned by a combination of solution concentration and thermal annealing. As transparent Joule heaters, even without optimization, these SCT devices show competitive performance compared to established technologies such as those based on reduced graphene oxide, and surpass the temperature stability limit of other materials. Furthermore, it is demonstrated that laser annealing can be used to process the SCT films and directly pattern transparent heaters on an arbitrary substrate. These results highlight the potential of SCT as a feedstock material for electronic applications and suggest that broader classes of either naturally occurring carbon or produced carbonaceous by-products could prove useful in a range of applications.

Rethinking Coal: Thin Films of Solution Processed Natural Carbon Nanoparticles for Electronic Devices.

Disordered carbon materials, both amorphous and with long-range order, have been used in a variety of applications, from conductive additives and contact materials to transistors and photovoltaics. Here we show a flexible solution-based method of preparing thin films with tunable electrical properties from suspensions of ball-milled coals following centrifugation. The as-prepared films retain the rich carbon chemistry of the starting coals with conductivities ranging over orders of magnitude, and thermal treatment of the resulting films further tunes the electrical conductivity in excess of 7 orders of magnitude. Optical absorption measurements demonstrate tunable optical gaps from 0 to 1.8 eV. Through low-temperature conductivity measurements and Raman spectroscopy, we demonstrate that variable range hopping controls the electrical properties in as-prepared and thermally treated films and that annealing increases the sp(2) content, localization length, and disorder. The measured hopping energies demonstrate electronic properties similar to amorphous carbon materials and reduced graphene oxide. Finally, Joule heating devices were fabricated from coal-based films, and temperatures as high as 285 °C with excellent stability were achieved.

Morphology control in block copolymer films using mixed solvent vapors.

Solvent vapor annealing of block copolymer thin films can produce a range of morphologies different from the equilibrium bulk morphology. By systematically varying the flow rate of two different solvent vapors (toluene and n-heptane) and an inert gas, phase maps showing the morphology versus vapor pressure of the solvents were constructed for 45 kg/mol polystyrene-block-polydimethylsiloxane diblock copolymer films of different thicknesses. The final morphology was correlated with the swelling of the block copolymer and homopolymer films and the solvent vapor annealing conditions. Self-consistent field theory is used to model the effects of solvent swelling. These results provide a framework for predicting the range of morphologies available under different solvent vapor conditions, which is important in lithographic applications where precise control of morphology and critical dimensions are essential.