The remarkable mechanical properties of carbon nanotubes arise from the exceptional strength and stiffness of the atomically thin carbon sheets (graphene) from which they are formed. In contrast, bulk graphite, a polycrystalline material, has low fracture strength and tends to suffer failure either by delamination of graphene sheets or at grain boundaries between the crystals. Now Stankovich et al. have produced an inexpensive polymer-matrix composite by separating graphene sheets from graphite and chemically tuning them. The material contains dispersed graphene sheets and offers access to a broad range of useful thermal, electrical and mechanical properties. Individual sheets of graphene can be readily incorporated into a polymer matrix, giving rise to composite materials having potentially useful electronic properties. Graphene sheets—one-atom-thick two-dimensional layers of sp2-bonded carbon—are predicted to have a range of unusual properties. Their thermal conductivity and mechanical stiffness may rival the remarkable in-plane values for graphite (∼3,000 W m-1 K-1 and 1,060 GPa, respectively); their fracture strength should be comparable to that of carbon nanotubes for similar types of defects1,2,3; and recent studies have shown that individual graphene sheets have extraordinary electronic transport properties4,5,6,7,8. One possible route to harnessing these properties for applications would be to incorporate graphene sheets in a composite material. The manufacturing of such composites requires not only that graphene sheets be produced on a sufficient scale but that they also be incorporated, and homogeneously distributed, into various matrices. Graphite, inexpensive and available in large quantity, unfortunately does not readily exfoliate to yield individual graphene sheets. Here we present a general approach for the preparation of graphene-polymer composites via complete exfoliation of graphite9 and molecular-level dispersion of individual, chemically modified graphene sheets within polymer hosts. A polystyrene–graphene composite formed by this route exhibits a percolation threshold10 of ∼0.1 volume per cent for room-temperature electrical conductivity, the lowest reported value for any carbon-based composite except for those involving carbon nanotubes11; at only 1 volume per cent, this composite has a conductivity of ∼0.1 S m-1, sufficient for many electrical applications12. Our bottom-up chemical approach of tuning the graphene sheet properties provides a path to a broad new class of graphene-based materials and their use in a variety of applications.

Graphene-based composite materials

Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Graphene sheets offer extraordinary electronic, thermal and mechanical properties and are expected to find a variety of applications. A prerequisite for exploiting most proposed applications for graphene is the availability of processable graphene sheets in large quantities. The direct dispersion of hydrophobic graphite or graphene sheets in water without the assistance of dispersing agents has generally been considered to be an insurmountable challenge. Here we report that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization. This discovery has enabled us to develop a facile approach to large-scale production of aqueous graphene dispersions without the need for polymeric or surfactant stabilizers. Our findings make it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.

/pdf/processable-aqueous-dispersions-of-graphene-nanosheets-4pl49qkwvn.pdf

Processable aqueous dispersions of graphene nanosheets

/pdf/self-assembled-monolayers-of-thiolates-on-metals-as-a-form-1neb0hj3k4.pdf

Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

In the last 10 years the field of molecular diagnostics has witnessed an explosion of interest in the use of nanomaterials in assays for gases, metal ions, and DNA and protein markers for many diseases. Intense research has been fueled by the need for practical, robust, and highly sensitive and selective detection agents that can address the deficiencies of conventional technologies. Chemists are playing an important role in designing and fabricating new materials for application in diagnostic assays. In certain cases assays based upon nanomaterials have offered significant advantages over conventional diagnostic systems with regard to assay sensitivity, selectivity, and practicality. Some of these new methods have recently been reviewed elsewhere with a focus on the materials themselves or as subclassifications in more generalized overviews of biological applications of nanomaterials.1-7 We intend to review some of the major advances and milestones in the field of detection systems based upon nanomaterials and their roles in biodiagnostic screening for nucleic acids, * To whom correspondence should be addressed. Phone: 847-4913907. Fax: 847-467-5123. E-mail: chadnano@northwestern.edu. Nathaniel L. Rosi earned his B.A. degree at Grinnell College (1999) and his Ph.D. degree from the University of Michigan (2003), where he studied the design, synthesis, and gas storage applications of metal−organic frameworks under the guidance of Professor Omar M. Yaghi. In 2003 he began postdoctoral studies as a member of Professor Mirkin’s group at Northwestern University. His current research focuses on the rational assembly of DNA-modified nanostructures into larger-scale materials.

/pdf/nanostructures-in-biodiagnostics-5553cs9yqw.pdf

Nanostructures in Biodiagnostics

Unilamellar colloids of graphite oxide (GO) were prepared from natural graphite and were grown as monolayer and multilayer thin films on cationic surfaces by electrostatic self-assembly. The multilayer films were grown by alternate adsorption of anionic GO sheets and cationic poly(allylamine hydrochloride) (PAH). The monolayer films consisted of 11−14 A thick GO sheets, with lateral dimensions between 150 nm and 9 μm. Silicon substrates primed with amine monolayers gave partial GO monolayers, but surfaces primed with Al13O4(OH)24(H2O)127+ ions gave densely tiled films that covered approximately 90% of the surface. When alkaline GO colloids were used, the monolayer assembly process selected the largest sheets (from 900 nm to 9 μm) from the suspension. In this case, many of the flexible sheets appeared folded in AFM images. Multilayer (GO/PAH)n films were invariably thicker than expected from the individual thicknesses of the sheets and the polymer monolayers, and this behavior is also attributed to folding...

http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/Che%20Mat11,%20771.pdf

Layer-by-Layer Assembly of Ultrathin Composite Films from Micron-Sized Graphite Oxide Sheets and Polycations

This letter describes an electric-field assisted assembly technique used to position individual nanowires suspended in a dielectric medium between two electrodes defined lithographically on a SiO2 substrate. During the assembly process, the forces that induce alignment are a result of nanowire polarization in the applied alternating electric field. This alignment approach has facilitated rapid electrical characterization of 350- and 70-nm-diameter Au nanowires, which had room-temperature resistivities of approximately 2.9 and 4.5×10−6 Ω cm.

Electric-field assisted assembly and alignment of metallic nanowires

±COOAr, m to ±CH2O±, m to ArCOO± and m to ±OOCAr), 7.25±7.32 (m, 4 Ar±H, o to ±CH2O± and o to ArCOO±), 6.96±7.04 (m, 4 Ar±H, o to ±OCH2(CH2)11± and o to ±OOCAr), 4.20 (t, 2H, ArOCH2CH2O±), 4.05 (t, 2 H, ArOCH2(CH2)10±, J=6.6 Hz), 3.54±4.00 (m, 68 H, ±CH2O±), 3.37 (s, 3 H, CH3O±), 1.77±1.85 (m, 2 H, ±CH2(CH2)9±), 1.14±1.47 (m, 18 H, ±CH2(CH2)9±), 0.87 (t, 3 H, CH3(CH2)11±, J=6.8 Hz). C-NMR (62.5 MHz, CDCl3) d 165.6, 165.4 164.0, 159.6, 151.0, 150.9, 146.4, 138.7, 138.4, 132.7, 131.2, 128.8, 128.6, 128.5, 127.9, 127.1, 122.6, 122.5, 121.9, 115.5, 114.7, 72.3, 71.3, 71.1, 71.0, 68.8, 68.0, 59.4, 32.3, 30.04, 29.99, 29.97, 29.8, 29.5, 26.4, 23.7, 23.1, 14.5: Anal. calcd for C79H116O23: C, 66.18; H, 8.15. Found: C, 66.72, H, 8.33. MW/Mn=1.03 (gel permeation chromatography).

Orthogonal Self‐Assembly on Colloidal Gold‐Platinum Nanorods

branes. The tubes are well ordered but somewhat tilted due to their relatively low mechanical strength compared with cylinders. The Raman spectra of the tubes have shown two broad peaks centered on 1345 and 1565 cm ‐1 , indicating that the tubes consist mainly of DLC. All the nanotubes have a uniform outer diameter of about 300 nm. The wall thickness of the tubes is very small, which can be controlled by optimizing the growth conditions. The tube length was about 7 lm, as in the case of cylinders. All the tubes have uniform height and are found to be hollow inside. Such nanotube arrays are probably useful for field emitters as well as for depositing metal catalysts or enzymes in the tubes, which in turn may be useful for new technologies. Other applications presumably include their use as porous electrodes in electrochemistry, as conductive diamond is known to exhibit outstanding electrochemical properties such as low background current, wide electrochemical potential window and high resistance to deactivation. [19] The present technique is a simple one for producing highly ordered diamond nanocylinders and nanotubes in high yield. The dimensions of these nanofibers are easily controllable by varying the pore dimensions of the alumina membrane. This technique enables others to adopt it easily and study the physical properties of these arrays for various applications in fieldemission displays, photonic bandgap materials, composite materials, and electrochemistry.

DNA‐Directed Assembly of Gold Nanowires on Complementary Surfaces

Alumina membranes containing 200 nm diameter pores were replicated electrochemically with metals (Au and Ag) to make free-standing nanowires several microns in length. Wet layer-by-layer assembly of nanoparticle (TiO2 or ZnO)/polymer thin films was carried out in the membrane between electrodeposition steps to give nanowires that contained rectifying junctions. Concentric structures with similar properties were prepared by first coating the membrane walls with multilayer films, and then growing nanowires inside the resulting tubules, or by growing films on the exposed surface of the nanowires after dissolution of the membrane. The I−V characteristics of nanowires prepared by either technique show current rectifying behavior. The electronic properties of Au(MEA)/(ZnO/PSS)19ZnO/Ag (MEA = mercaptoethylamine) devices indicate that rectification is determined by charge injection at the metal/ZnO/PSS-film interface rather than by a tunneling mechanism. In the case of Ag(TiO2/PSS)9TiO2/Au devices, switching beha...

Benjamin R. Martin

Papers

Layer-by-Layer Assembly of Ultrathin Composite Films from Micron-Sized Graphite Oxide Sheets and Polycations

Electric-field assisted assembly and alignment of metallic nanowires

Orthogonal Self‐Assembly on Colloidal Gold‐Platinum Nanorods

DNA‐Directed Assembly of Gold Nanowires on Complementary Surfaces

Layer-by-Layer Assembly of Rectifying Junctions in and on Metal Nanowires †