Advanced Materials

Interactions of polyelectrolytes with oppositely charged surfactants can give rise to highly ordered structures (e.g., see Figure) that have potential use in various industries, such as the medical, food, and coating industries. This review focuses on colloidal and gel polyelectrolyte–surfactant complexes, including the resulting nanostructures. Physicochemical studies of DNA–surfactant complexes are also presented.

The use of semicrystalline polymers for surface structuring allows multiple embossing and structuring of oriented polymer films, in contrast to amorphous polymers. The Figure shows an oriented perfluorinated polymer film (FEP), on which a lamellar grating has been superimposed by solid-state embossing. Polarized optical microscopy reveals the combined optical effects of surface structure and molecular orientation.

Bis-urea-oligothiophene (U2Tn) molecules are promising candidates for the construction of 1D semiconducting channels because of their strong tendency to self-aggregate in solution into elongated 1D arrays. Here is reported the self-assembly of low-dimensional aggregates of U2Tn molecules onto several substrates (the Figure shows aggregation into directed fibers on a silica surface).

Cyclodextrins can act as hosts for heteroaromatic compounds to produce stable, odorless, complexes that can be oxidatively polymerized in water, it is reported here. The preparation and structural analysis of ratio 1:1 host–guest complexes for several types of cyclodextrin with pyrrole or 3,4-ethylenedioxythiophene (see Figure), and their reaction in water to give conjugated polymers are presented here (see also cover).

Free-standing colloids of gallium nitride have been synthesized from azide-based “single-source” precursors—molecules that contain both the metal and nitrogen—e.g., [Et₂Ga(N₃)]₃. The solution synthesis is described and the examination of the resulting colloids by dynamic light scattering, transmission electron microscopy, etc. detailed. GaN is an important III–V semiconductor with applications in light-emitting diodes, lasers, sensors, and high-temperature electron devices, and it is suggested that in the future a solution preparation of such devices may become possible on the basis of GaN colloidal chemistry.

Carbon nanotubes are very promising candidates for molecular wires, and as such it is important to understand their electrical and mechanical properties. Here single-walled carbon nanotubes (SWNTs) are investigated using non-contact dynamic scanning force microscopy (SFM). The nanotubes are locally probed using metallized cantilever tips to correlate the mechanical and electrical properties, and the simultaneously obtained force vs. distance and current vs. distance curves are compared. The measurements reveal that electrical contact occurs for very small load forces.

A facile approach to engineering diverse mixed-colloid ensembles is presented here. Various colloid architectures are seen that are controlled by both electrostatic self-assembly and concentration changes (see Figure) regardless of the nature of the nanoparticle core. The methodology should be applicable to the creation of functionally diverse materials via combinatorial chemistry (see also inside front cover).

Macromolecular fractionation of rod-like polymers at solid–liquid interfaces is monitored by STM imaging of the polymer chains self-assembled on graphite (see Figure). It is concluded that the competition between entropic losses and enthalpic gains favors the adsorption of the longest chains, which are still sufficiently straight. The phenomenon may be used to fractionate stiff polydisperse macromolecules.

Ordered arrays of nickel nanowires have been prepared using pulsed electrodeposition. Two self-patterning anodization processes were used to fabricate alumina pore matrices into which nickel was deposited from a Watts bath: two short millisecond deposition pulses followed by a long delay yielded almost 100 % filled pores (see Figure). Nanowire arrays are expected to have important applications as magnetic memories.

Uniform molecular alignment of the conducting liquid-crystal polymer shown has been achieved by means of a simple rubbing technique. Surprisingly, the molecules were found to align themselves so that the alkoxy side chains—not the mesogenic main chain—lie parallel to the rubbing direction. This anomalous alignment was confirmed using Raman, absorption, and photoluminescence spectroscopy.

Circularly polarized photoluminescence has been observed from chiral π-conjugated polymers (e.g., see Figure). It was found that the degree of circular polarization was greater in the absorption than in the emission, which is interpreted in terms of trap sites acting as luminescent centers. These results may be important for the fabrication of LEDs for producing circularly polarized light.

Room-temperature white light emission can be obtained from a family of europium-containing hybrid materials called di-ureasils—organically modified silicates in which oxyethylene chains of different length are grafted by means of urea crosslinks to the siliceous backbone. It is demonstrated that the emission color may be tuned by either adjusting the amount of europium salt incorporated or by varying the excitation wavelength. The Judd–Ofelt intensity parameters are obtained and considered together with the decay rates and an interpretation of the physical meaning of the observed behavior is offered.

Conjugated polymer thin films with metal centers in the backbone may be effectively prepared by electropolymerization, as described here. Monomers such as the oligothienylferrocene complex shown in the Figure are used, resulting in polymers that maintain some of the desirable features of organic conjugated polymers whilst also displaying interesting new properties.

NMR spectroscopy is a powerful method for the characterization of materials. Here the development of double resonance NMR experiments is summarized and their application to materials science highlighted using the synthesis of silicon nanoclusters within aluminosilicate molecular sieves (see Figure) as an example. Not only can the structure of the product be elucidated but also that of the reaction intermediates.