Advanced Materials

The physicochemical aspects of surface-initiated polymer films used to modify planar and non-planar surfaces and to produce micro- and nanoscale patterned features (see Figure) are reviewed. Recent advances in the use of responsive polymer films and uses of surface-initiated polymer films to modify materials properties and impact applications in chromatography, nanoparticle-templated synthesis, and carbon nanotube dispersion are highlighted.

An all-in-one device for fabricating microfluidic devices is developed by modifying a commercially available liquid-crystal-display projector. Micropatterns are formed on photosensitive materials from images that are prepared using personal-computer software. Desired poly(dimethylsiloxane) microfluidic channels (see Figure) are obtained rapidly without the need for expensive photomasks and light sources.

Tris(quinolate)Al^III (Alq₃)-based metallocomplexes with electron- deficient or electron-rich aryl substituents display remarkable blue-to-red tuning of both photo- and electroluminescence, covering most of the visible-light region (see Figure). The correlation between the electronic properties of the aryl substituents, highest occupied–lowest unoccupied molecular orbital (HOMO–LUMO) gap, and the emissive properties of the complexes suggests this approach may be used to design new light-emitting materials.

The first successful synthesis of iridium complexes {(PEP)₂Ir(acac), (NEP)₂Ir(acac), (PETP)₂Ir(acac), (MPEP)₂Ir(acac), and (PP)₂Ir(acac)} (see Figure) using an olefin-tethered pyridine ring is described. The electroluminescent devices prepared using these iridium complexes as dopant emitters showed very high brightness and efficiencies.

A biodegradable microfabrication platform for constructing 3D high- resolution devices for tissue engineering and drug delivery is presented. Biodegradable polymer films with built-in micrometer-scale features are stacked and fusion bonded to construct fully biodegradable, poly(DL-lactic-co-glycolide) (PLGA)-based, monolithic, multilayer, microfluidic networks. Integration with cells or drug compounds will enable use of these devices in therapeutic applications (scale bar: ∼ 300 μm).

Mesoporous Li₃Fe₂(PO₄)₃ battery electrode materials (see Figure) with a discharge capacity of 140 mAh g^–1 at 20 mA g^–1 self-assemble under aqueous conditions using a cationic surfactant as the template. Mössbauer spectroscopy results are characteristic of Fe³⁺ ions in oxides, while the interaction of lithium with Fe and O in mesoporous Li₃Fe₂-(PO₄)₃ is verified by ⁷Li NMR. This synthetic strategy may be applied to the production of other multi-metal phosphate ordered mesoporous structures.

Crystalline organic films formed by self-assembly of 2,2-dimethyl-α,α,α′,α′-tetraphenyldioxolane-4,5-dimethanol and coumarin molecules can be used for ultrahigh-density data storage. A 3 × 4 matrix pattern (see Figure) was recorded by applying voltage pulses between a scanning tunneling microscope tip and the film. Regulating the amplitude and width of the applied pulsed voltage allows a data storage density of about 10¹³ bits cm^–2 to be achieved.

SiC particles are coated with multi-walled carbon nanotubes using a simple chemical vapor deposition process. This new type of micro/nanoscale hybrid reinforcement combines the characteristics of carbon nanotubes and the micrometer-sized SiC particles. Using this hybrid reinforcement in an epoxy composite produced a significant improvement in mechanical properties, attributed to the carbon-nanotube- reinforced interface between the epoxy matrix and the particles.

Depositing metal layers onto a self-assembled monolayer (SAM) is achieved using a new technique. Au(111) bearing a 4,4′-dithiodipyridine SAM is immersed into a Pd^II solution without potential control, causing Pd^II to adsorb on the surface by forming a complex with the pyridine species. The Pd^II ions are then electrochemically reduced to Pd⁰ (see Figure). Angle-resolved X-ray photoelectron spectroscopy measurements unequivocally show that the reduced Pd resides on top of the SAM.

Enhanced field emission from ZnO nanowires grown on carbon cloth (see Figure) has been measured. These emitters produced a field emission current density of 1 mA cm^–2 at about 0.7 V μm^–1, corresponding to an exceptionally high field-enhancement factor of 4.11 × 10⁴. Such an extremely high field-enhancement factor is believed to be the combined effect of the high aspect ratio of ZnO nanowires and the geometry of the carbon-cloth substrate.

The development and performance of tetraphenyldiaminobiphenyl-based polymer composites with stable video-rate-compatible response times over large exposures is reported (see Figure). The high diffraction efficiency together with an exposure-history independence of the response time described is a significant advance for developing an all-organic photorefractive composite for device applications.

Fully dense ceramic–carbon-nanotube composites with homogeneously distributed multiwalled carbon nanotubes (MWCNTs) (see Figure; inset shows a single MWCNT) have been synthesized by a unique method, which uses a polymer-derived ceramic as the composite matrix. Composites with an MWCNT fraction of 6.4 vol.-% had significantly increased Young's moduli, hardness, and damage resistance, compared to the values for the pure ceramic matrix.

Organic light-emitting devices (OLEDs) formed by soft-contact lamination (ScL) show high luminous efficiency (∼ 2.25 cd A^–1 with a Au electrode) and better operational stability than similar devices fabricated by thermal evaporation. The laminated electrodes consist of thin films of Au supported by flat or structured elastomeric elements of polydimethylsiloxane. By combining ScL and soft lithography, it is possible to fabricate high-efficiency OLEDs with micrometer-scale light-emitting areas.

Thin films of multiwalled carbon nanotubes (MWNTs) deposited on cellulose fiber filters (see Figure) are evaluated as particulate filtration media. Even for very low MWNT coverages (∼0.07 mg cm^–2), these filters exhibit efficiencies greater than 99 % for airborne fine particles. The pore structure and quality of the nanotube-based filters have also been characterized.

Carbon nanotube field-effect transistors (NTFETs) coated with poly(ethyleneimine) (PEI) and starch polymers exhibit electrical conductance changes upon exposure to CO₂ gas in air at ambient temperature (see Figure). This observation has furnished nanoelectronic CO₂ sensors. Their small size and low power consumption has enormous potential in wireless sensing for industrial and medical CO₂ sensor units.

Dense arrays of vertically aligned titania nanotubes (see Figure) are created directly on silicon substrates by combining atomic layer deposition with an alumina template-based fabrication approach. This method enables excellent control over the nanotube dimensions, including their wall thickness, diameter, and height. Nanotubes were fabricated with tube walls thin enough (< 3 nm) to exhibit a wall-thickness- dependent blue-shift in the optical absorption spectra of the arrays.

Porous carbons with mesoporous walls (see Figure) are produced by template replication of aggregates of small silica particles, which were themselves templated by a self-assembled lattice of larger monodisperse polystyrene spheres. A direct methanol fuel cell using the new material as a catalyst support shows significantly improved performance due to the combination of high surface area and facile fuel and product diffusion.

Uniform nanofibers composed of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] and its blends with poly(3-hexylthiophene) are formed by co-electrospinning their solutions with poly(vinyl pyrrolidone) (PVP) through a coaxial capillary system, followed by extraction of the PVP phase (see Figure). Compared with spin-cast films, the fibers show reduced phase separation and improved energy-transfer efficiency.