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 selfassembly. 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 Å 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 Al 13 O 4 -(OH) 24 (H 2 O) 12 7+ 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 of the sheets. Multilayer (GO/PAH) n and (GO/ polyaniline) n films grown between indium-tin oxide and Pt electrodes show diodelike behavior, and higher currents are observed with the conductive polyaniline-containing films. The resisitivity of these films is decreased, as expected, by partial reduction of GO to carbon.

Ordered mesoporous polymers have been prepared by replication of colloidal crystals made from silica spheres 35 nanometers in diameter. The pores in the colloidal crystals were filled with divinylbenzene (DVB), ethyleneglycol dimethacrylate (EDMA), or a mixture of the two. Polymerization and subsequent dissolution of the silica template leaves a polycrystalline network of interconnected pores. When mixtures of DVB and EDMA are used, the pore size of the polymer replicas can be varied continuously between 35 and 15 nanometers because the polymer shrinks when the silica template is removed.

Zeolites were used as templates to prepare microporous polymer replicas. Phenolformaldehyde polymers were synthesized and cured within the channel networks of zeolites Y, β, and L. Dissolution of the aluminosilicate framework in aqueous HF yields an organic replica that contains <2% aluminosilicate. The zeolite template exerts important topological effects on the structure and physical properties of the replica. Using zeolites Y and β, which have three-dimensionally interconnected channel structures, the microporosity of the template is reflected in the replica polymer. Pore size distributions are consistent with the predominance of 5-6 Å walls in the parent zeolite. In contrast, complete collapse of the replica, to a give nonporous material, occurs upon removal of the zeolite L template, since the latter has a one-dimensional channel structure. TEM and SEM micrographs also show evidence of collapse in the latter case. Pyrolysis of the zeolite-resin composites at 900 °C, and subsequent etching, produces very high surface area, electronically conducting replicas. Under these conditions the zeolite Y replica has markedly lower conductivity than those obtained from β and L, which have straight channels.

Chimie douce", or soft chemistry, represents a simple and useful route to metastable solid-state compounds. These terms have historically been used to describe several types of low-temperature solid-solid transformations such as intercalation/deintercalation, ion exchange, hydrolysis, and redox reactions. 2 The common feature of soft chemical reactions is that they produce metastable compounds that are structurally related to the parent solid, by preserving the atomic connectivity of small building blocks and/or extended structural elements. Some interesting examples of unusual phases made by soft chemistry include ReO 3like MoO 3 , 3 Ti 2 Nb 2 O 9 , 4 hexagonal WO 3 , 5 TiO 2 -B, 6 VS 2 , 7 and layered double hydroxides. 8 In general, it is not possible to prepare these compounds using high-temperature routes. Some of these low-temperature compounds have special properties, such as reversible intercalation, photoconductivity, or catalytic activity, which are not found in high-temperature, stable phases of the same composition.We report in this paper a chimie douce reaction that converts a layered perovskite phase into a metastable three-dimensional perovskite. The topochemical transformation is illustrated in Figure 1. In this series of reactions, the lamellar compound K 2 SrTa 2 O 7 and isostructural K 2 SrTa 2-x Nb x O 7 (x ) 0.2, 0.4) are first ionexchanged to the corresponding acid forms and then topochemically dehydrated to yield metastable perovskite phases SrTa 2 O 6 and SrTa 2-x Nb x O 6 . The process is similar to that previously reported for ion-exchange and condensation of K 2 Ln 2 Ti 3 O 10 . 10 Further heating causes the transformation to the structurally unrelated tetragonal tungsten bronze phases of the same composition. This transformation is interesting because K 2 -SrTa 2 O 7 is a member of a large class of structurally related compounds 9 (the Ruddlesden-Popper phases,

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