John M. Mitchels

Monodisperse cylindrical micelles by crystallization-driven living self-assembly

Non-spherical nanostructures derived from soft matter and with uniform size-that is, monodisperse materials-are of particular utility and interest, but are very rare outside the biological domain. We report the controlled formation of highly monodisperse cylindrical block copolymer micelles (length dispersity < or = 1.03; length range, approximately 200 nm to 2 microm) by the use of very small (approximately 20 nm) uniform crystallite seeds that serve as initiators for the crystallization-driven living self-assembly of added block-copolymer unimers with a crystallizable, core-forming metalloblock. This process is analogous to the use of small initiator molecules in classical living polymerization reactions. The length of the nanocylinders could be precisely controlled by variation of the unimer-to-crystallite seed ratio. Samples of the highly monodisperse nanocylinders of different lengths that are accessible using this approach have been shown to exhibit distinct liquid-crystalline alignment behaviour.

Main‐Chain Heterobimetallic Block Copolymers: Synthesis and Self‐Assembly of Polyferrocenylsilane‐b‐Poly(cobaltoceniumethylene)

Two metals are better than one: Main-chain heterometallic block copolymers composed of iron- and cobalt-rich blocks (see picture) were synthesized through consecutive photocontrolled ring-opening polymerization (ROP) of sila[1]ferrocenophanes and dicarba[2]cobaltocenophanes followed by oxidation of the cobaltocene-containing block. The redox properties and self-assembly of the resulting block copolymers in solution were also studied.

Functionalized carbon nanoparticles, blacks and soots as electron-transfer building blocks and conduits.

Functionalized carbon nanoparticles (or blacks) have promise as novel active high-surface-area electrode materials, as conduits for electrons to enzymes or connections through lipid films, or as nano-building blocks in electroanalysis. With previous applications of bare nanoblacks and composites mainly in electrochemical charge storage and as substrates in fuel cell devices, the full range of benefits of bare and functionalized carbon nanoparticles in assemblies and composite (bio)electrodes is still emerging. Carbon nanoparticles are readily surface-modified, functionalized, embedded, or assembled into nanostructures, employed in bioelectrochemical systems, and incorporated into novel electrochemical sensing devices. This focus review summarizes aspects of a rapidly growing field and some of the recent developments in carbon nanoparticle functionalization with potential applications in (bio)electrochemical, photoelectrochemical, and electroanalytical processes.

Hydrothermal conversion of one-photon-fluorescent poly-(4-vinylpyridine) into two-photon-fluorescent carbon nanodots

A novel two-photon-fluorescent N,O-heteroatom-rich carbon nanomaterial has been synthesized and characterized. The new carbon nanoparticles were produced by hydrothermal conversion from a one-photon-fluorescent poly(4-vinylpyridine) precursor (P4VP). The carbonized particles (cP4VP dots) with nonuniform particle diameter (ranging from sub-6 to 20 nm with some aggregates up to 200 nm) exhibit strong fluorescence properties in different solvents and have also been investigated for applications in cell culture media. The cP4VP dots retain their intrinsic fluorescence in a cellular environment and exhibit an average excited-state lifetime of 2.0 ± 0.9 ns in the cell. The cP4VP dots enter HeLa cells and do not cause significant damage to outer cell membranes. They provide one-photon or two-photon fluorescent synthetic scaffolds for imaging applications and/or drug delivery.

Facile preparation and processing of aqueous dispersions of tris(8-hydroxyquinoline) aluminium(III) photoluminescent nanoparticles

In this paper we present a facile method for the novel production of surfactant-stabilized aqueous dispersions of tris(8-hydroxyquinoline) aluminium(III) (Alq3) nanoparticles. The nanoparticles are spherical, less than 10 nm in mean diameter, and highly fluorescent. We demonstrate the potential scope of these water-based colloids in sol–gel and electrospinning processes by fabricating photoluminescent silica glasses and polymer nanowires, respectively. Furthermore, we show that the Alq3 nanoparticles are effective imaging agents for electroporated or thin-sectioned MCF-7 cells. The development of aqueous-based approaches to stable sols of Alq3 nanoparticles offers significant scope for the future use and application of this technologically important emissive material.

Intrinsically Microporous Polymer Retains Porosity in Vacuum Thermolysis to Electroactive Heterocarbon.

Vacuum carbonization of organic precursors usually causes considerable structural damage and collapse of morphological features. However, for a polymer with intrinsic microporosity (PIM-EA-TB with a Brunauer-Emmet-Teller (BET) surface area of 1027 m(2)g(-1)), it is shown here that the rigidity of the molecular backbone is retained even during 500 °C vacuum carbonization, yielding a novel type of microporous heterocarbon (either as powder or as thin film membrane) with properties between those of a conducting polymer and those of a carbon. After carbonization, the scanning electron microscopy (SEM) morphology and the small-angle X-ray scattering (SAXS) Guinier radius remain largely unchanged as does the cumulative pore volume. However, the BET surface area is decreased to 242 m(2)g(-1), but microporosity is considerably increased. The new material is shown to exhibit noticeable electrochemical features including two pH-dependent capacitance domains switching from ca. 33 Fg(-1) (when oxidized) to ca. 147 Fg(-1) (when reduced), a low electron transfer reactivity toward oxygen and hydrogen peroxide, and a four-point-probe resistivity (dry) of approximately 40 MΩ/square for a 1-2 μm thick film.

A Raman spectroscopic study of uranyl minerals from Cornwall, UK

In the fields of nuclear forensics, geology and environmental science, it is important to be able to rapidly identify an unknown sample of uranyl mineral. Raman spectroscopy provides a fast, non-destructive and portable strategy for collecting data, which can then be compared against a set of known experimental information. We present a Raman study of a selection of uranyl minerals from Cornwall, UK. This includes the first Raman spectrum published for the uranyl arsenate mineral, novaekite. These spectra were collected under a standard set of conditions, using three excitation wavelengths, 325, 532 and 785 nm, the latter typically providing spectra with little fluorescence and the best resolution. The vibrational properties of these minerals are characterised by the symmetric stretching mode of the uranyl cation, seen between 750–900 cm−1, though the exact position varies with respect to the local environment. To discriminate between samples, the rest of the spectrum must be considered; the poly-anions in the structure provide a fingerprint set of Raman bands. An added complication occurs when samples of the same mineral from different mines demonstrate variations in their Raman spectra; this emphasises the need for data to be collected from a variety of locations, but also suggests that other experimental techniques could provide complementary information.

Surface State Trapping and Mobility Revealed by Junction Electrochemistry of Nano-Cr2O3

Hydrous chromium oxide nanoparticles (~15 nm diameter) are assembled from a colloidal solution onto tin-doped indium oxide (ITO) substrates by layer-by-layer electrostatic deposition with aqueous carboxymethyl-cellulose sodium salt binder. Calcination produces purely inorganic mesoporous films (average thickness increase per layer of 1 nm) of chromia Cr2O3. When immersed in aqueous carbonate buffer at pH 10 and investigated by cyclic voltammetry, a chemically reversible oxidation is observed because of a conductive layer at the chromia surface (formed during initial potential cycling). This is attributed to a surface CrIII/IV process. At more positive potentials higher oxidation states are accessible before film dissolution. The effects of film thickness and pH on voltammetric responses are studied. X-Ray photoelectron spectroscopy (XPS) evidence for higher chromium oxidation states is obtained. ITO junction experiments are employed to reveal surface conduction by CrIII/IV and CrIV/V ‘mobile surface states’ and an estimate is obtained for the apparent CrIII/IV charge surface diffusion coefficient Dapp = 10–13 m2 s–1. The junction experiment distinguishes mobile surface redox sites from energetically distinct deeper-sitting ‘trapped states’.

Magnetically enhanced plasma coating of nanostructures with ultrathin diamond-like carbon films

Diamond-like carbon (DLC) films are widely used as protective coatings in a variety of technical macro- and micro-applications. However, most of the widely-used coating methods are not suitable for nanoscale applications. In this work, the method of magnetically enhanced plasma deposition (MEPCVD) was employed for the coating of AFM probes and free-standing nanostructures with 3–20 nm thick DLC films. The carbon bonding structure, mechanical and tribological properties of the films as well as the anisotropy of the coatings and its effect on the shape of nanoscale features were investigated and it is shown that the method employed produces very smooth coatings (roughness below 0.2 nm) with a significantly lower than usual internal stress of 0.5–0.8 GPa. Wear tests of AFM probes at a high load (1 μN) showed that the DLC coating decreases their wear rate by two orders of magnitude. It was found that coating of free-standing nanostructures even with ultrathin DLC films may cause their deformation due to the interface stress when the coating is asymmetric.

“Hydrothermal wrapping” with poly(4-vinylpyridine) introduces functionality: pH-sensitive core–shell carbon nanomaterials

Negatively charged carbon nanoparticles (surface-phenylsulfonated) are “wrapped” in a poly(4-vinylpyridine) cationomer and hydrothermally converted into a pH-responsive core–shell nano-composite. With a “thin shell” this nano-material (ca. 20–40 nm diameter) is water-insoluble but readily dispersed into ethanol and deposited onto electrodes. Zeta-potential measurements suggest a point of zero charge (PZC) at ca. pH 4.5 with negative functional groups dominating in the more alkaline range and positive functional groups dominating in the acidic range. XPS data suggest carboxylate and pyridinium-like functional groups. This is further confirmed in voltammetric measurements for adsorbed cations (methylene blue) and adsorbed anions (indigo carmine). The specific capacitance reaches a maximum of 13 F g−1 at the PZC explained here tentatively by a “shell charging” effect within the nanoparticle shell.