Edward T. Samulski

Synthesis of water soluble graphene.

A facile and scalable preparation of aqueous solutions of isolated, sparingly sulfonated graphene is reported. (13)C NMR and FTIR spectra indicate that the bulk of the oxygen-containing functional groups was removed from graphene oxide. The electrical conductivity of thin evaporated films of graphene (1250 S/m) relative to similarly prepared graphite (6120 S/m) implies that an extended conjugated sp (2) network is restored in the water soluble graphene.

Continuous liquid interface production of 3D objects

Fast, continuous, 3D printing Although three-dimensional (3D) printing is now possible using relatively small and low-cost machines, it is still a fairly slow process. This is because 3D printers require a series of steps to cure, replenish, and reposition themselves for each additive cycle. Tumbleston et al. devised a process to effectively grow solid structures out of a liquid bath. The key to the process is the creation of an oxygen-containing “dead zone” between the solid part and the liquid precursor where solidification cannot occur. The precursor liquid is then renewed by the upward movement of the growing solid part. This approach made structures tens of centimeters in size that could contain features with a resolution below 100 µm. Science, this issue p. 1349 Solid parts are elevated from a liquid resin pool at a speed of hundreds of millimeters per hour. Additive manufacturing processes such as 3D printing use time-consuming, stepwise layer-by-layer approaches to object fabrication. We demonstrate the continuous generation of monolithic polymeric parts up to tens of centimeters in size with feature resolution below 100 micrometers. Continuous liquid interface production is achieved with an oxygen-permeable window below the ultraviolet image projection plane, which creates a “dead zone” (persistent liquid interface) where photopolymerization is inhibited between the window and the polymerizing part. We delineate critical control parameters and show that complex solid parts can be drawn out of the resin at rates of hundreds of millimeters per hour. These print speeds allow parts to be produced in minutes instead of hours.

The measurement of cross-relaxation effects in the proton NMR spin-lattice relaxation of water in biological systems: Hydrated collagen and muscle

Abstract A general procedure for investigating cross relaxation is presented. Experimental evidence derived from proton NMR studies of collagen and muscle clearly shows that cross relaxation between the bulk of the water protons and the bulk of macromolecular protons significantly perturbs water spin-lattice relaxation. These findings have serious implications for interpretations of the molecular dynamics of water molecules in hydrated biological systems. The presence of cross relaxation is direct proof that a fraction of the water protons exchange at a rate slow compared with the Larmor frequency.

Extraction of a hydrophilic compound from water into liquid CO2 using dendritic surfactants

Dendrimers are well defined, highly branched polymers that adopt a roughly spherical, globular shape in solution. Their cores are relatively loosely packed and can trap guest molecules, and by appropriate functionalization of the branch tips the macromolecules can act as unimolecular micelle-like entities. Here we show that dendrimers with a fluorinated shell are soluble in liquid carbon dioxide and can transport CO2-insoluble molecules into this solvent within their cores. Specifically, we demonstrate the extraction of a polar ionic dye, methyl orange, from water into CO2 using these fluorinated dendrimers. This observation suggests possible uses of such macromolecules for the remediation of contaminated water, the extraction of pharmaceutical products from fermentation vessels, the selective encapsulation of drugs for targeted delivery and the transport of reagents for chemical reactions (such as polymerization) in liquid and supercritical CO2 solvents.

Design of Nonionic Surfactants for Supercritical Carbon Dioxide

Interfacially active block copolymer amphiphiles have been synthesized and their self-assembly into micelles in supercritical carbon dioxide (CO2) has been demonstrated with small-angle neutron scattering (SANS). These materials establish the design criteria for molecularly engineered surfactants that can stabilize and disperse otherwise insoluble matter into a CO2 continuous phase. Polystyrene-b-poly(1,1-dihydroperfluorooctyl acrylate) copolymers self-assembled into polydisperse core-shell-type micelles as a result of the disparate solubility characteristics of the different block segments in CO2. These nonionic surfactants for CO2 were shown by SANS to be capable of emulsifying up to 20 percent by weight of a CO2-insoluble hydrocarbon into CO2. This result demonstrates the efficacy of surfactant-modified CO2 in reducing the large volumes of organic and halogenated solvent waste streams released into our environment by solvent-intensive manufacturing and process industries.

Photonic Crystal Geometry for Organic Solar Cells

We report organic solar cells with a photonic crystal nanostructure embossed in the photoactive bulk heterojunction layer, a topography that exhibits a 3-fold enhancement of the absorption in specific regions of the solar spectrum in part through multiple excitation resonances. The photonic crystal geometry is fabricated using a materials-agnostic process called PRINT wherein highly ordered arrays of nanoscale features are readily made in a single processing step over wide areas (approximately 4 cm(2)) that is scalable. We show efficiency improvements of approximately 70% that result not only from greater absorption, but also from electrical enhancements. The methodology is generally applicable to organic solar cells and the experimental findings reported in our manuscript corroborate theoretical expectations.

Hydrothermal synthesis of one-dimensional ZnO nanostructures with different aspect ratios

1-D ZnO nanorods with different aspect ratios were synthesized by a one-step, hydrothermal method. The ZnO nanorods grow along the [0001] direction to form single crystals. The experimental results reveal that the growth of polar inorganic crystals is sensitive to the reaction solvents.

The Patterning of Sub-500 nm Inorganic Oxide Structures†

Elastomeric perfluoropolyether molds are applied to pattern arrays of sub-500 nm inorganic oxide features. This versatile soft-lithography technique can be used to pattern a wide range of materials; in this work inorganic oxides including TiO2 , SnO2 , ZnO, ITO, and BaTiO3 are patterned on a variety of substrates with different aspect ratios. An example of TiO2 posts is shown in the figure.

Chain ordering and molecular orientational order in liquid crystals

We have extended the scheme for computing deuterium quadrupolar splittings of a flexible solute in a nematic solvent [Ferroelectrics 30, 83 (1980)] to study chain ordering in the 4‐n‐alkyl‐4′‐cyanobiphenyl liquid crystals (nCB). All possible configurations {φ} of the nCB molecule are generated by the rotational isomeric state model of Flory. Each {φ} has a separate ordering matrix whose diagonal elements are assumed to scale with the shape anisotropy of the molecule as prescribed by the principal moments of inertia of the configuration I{φ}. Two models for identifying the molecular‐fixed‐frame are considered: (1) The frame diagonalizes I{φ}; (2) the frame is stationary on the nCB core. The variation of deuterium quadrupolar splittings along the alkyl chain can be satisfactorily explained by the calculations, however, the detailed behavior of the computed splittings are sensitive to the assumptions about the placement of the molecular‐fixed‐frame.

Nanoforest Nb2O5 Photoanodes for Dye-Sensitized Solar Cells by Pulsed Laser Deposition

Vertically aligned bundles of Nb(2)O(5) nanocrystals were fabricated by pulsed laser deposition (PLD) and tested as a photoanode material in dye-sensitized solar cells (DSSC). They were characterized using scanning and transmission electron microscopies, optical absorption spectroscopy (UV-vis), and incident-photon-to-current efficiency (IPCE) experiments. The background gas composition and the thickness of the films were varied to determine the influence of those parameters in the photoanode behavior. An optimal background pressure of oxygen during deposition was found to produce a photoanode structure that both achieves high dye loading and enhanced photoelectrochemical performance. For optimal structures, IPCE values up to 40% and APCE values around 90% were obtained with the N(3) dye and I(3)(-)/I(-) couple in acetonitrile with open circuit voltage of 0.71 V and 2.41% power conversion efficiency.