Conjugated polydiacetylene (PDA)/silica nanocomposites with tunable mesostructures and reversible thermochromatism were synthesized through self-directed assembly of diacetylenic silanes. In contrast to the previous studies, where the PDA side chains interacted weakly through noncovalent interactions, the side chains in the present nanocomposites are covalently connected to the inorganic silica frameworks, providing control over the molecular alignment, stability, and electronic properties. Furthermore, tuning the molecular architecture (e.g., the shape and side-chain length) allows control over the mesostructure (e.g., cubic and lamellar) and chromatic response of the nanocomposites (from irreversible to partially reversible and then to completely reversible). As a result of the covalent interactions, the nanocomposites also demonstrate higher reversible chromatic transition temperatures. This work not only provides responsive robust chromatic materials toward practically reusable PDA sensors but also is of great fundamental value for the design of supramolecular assembly and the understanding of the chromatic mechanism of PDA.

Responsive PMO materials have been synthesized through co-assembly of bridged diacetylenic silsesquioxane and surfactant. The spatially defined polydiacetylenic component, mesoporous network, and the covalent proximity of polydiacetylene to silica endow the PMO with mechanical robustness, reversible chromatic responses, improved thermal stability, and faster responses to chemical stimuli. This research also provides an efficient molecular design and assembly paradigm to fabricate a family of conjugated optoelectronic materials, creating novel platforms for sensors, actuators, and other device applications.

We report a general and facile method to prepare free-standing, patternable nanoparticle/polymer monolayer arrays by interfacial NP assembly within a polymeric photoresist. The ultrathin monolayer nanoparticle/polymer arrays are sufficiently robust that they can be transferred to arbitrary substrates and suspended as free-standing membranes over cm-sized holeseven with free edges. More importantly, the polymethylmethacrylate (PMMA) in the system serves as a photoresist enabling two modes of electron beam (e-beam) patterning. Lower e-beam doses direct differential nanoparticle solubility and result in nanoparticle patterns with somewhat diffuse interfaces. At higher e-beam doses the PMMA serves as a negative resist resulting in submicrometer patterns with edge roughness comparable to that of the nanoparticle diameter. These ultrathin films of monolayer nanoparticle arrays are of fundamental interest as 2D artificial solids for electronic, magnetic, and optical properties and are also of technological interest for a diverse range of applications in micro- and macroscale devices including photovoltaics, sensors, catalysis, and magnetic storage.

Hollow silica microspheres encapsulating ferromagnetic iron oxide nanoparticles were synthesized by a surfactant-aided aerosol process and subsequent treatment. The cationic surfactant cetyltrimethyl ammonium bromide (CTAB) played an essential role in directing the structure of the composite. Translation from mesoporous silica particles to hollow particles was a consequence of increased loading of ferric species in the precursor solution and the competitive partitioning of CTAB between silicate and ferric colloids. The hypothesis was that CTAB preferentially adsorbed onto more positively charged ferric colloids under acidic conditions. At a critical Fe/Si ratio, most of the CTAB was adsorbed onto ferric colloids and coagulated the colloids to form larger clusters. During the aerosol process, a silica shell was first formed due to the preferred silicate condensation on the gas-liquid interface of the aerosol droplet. Subsequent drying concentrated the ferric clusters inside the silica shell and resulted in a silica shell/ferric core particle. Thermal treatment of the core shell particle led to encapsulation of a single iron oxide nanoparticle inside each silica hollow microsphere.

Topochemically polymerized sodium 10,12-pentacosadiynoate (PCDA-Na) microcrystals show an irreversible red-to-blue chromatic transition accompanied by a distinct structural evolution upon initial thermal treatment, and show a subsequent completely reversible blue-to-red chromatic transition upon further thermal stimuli. Visible absorption spectroscopy, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) are used to investigate the thermochromatic transition behavior of the polydiacetylenic microcrystals. Brief quantum mechanical geometry optimization is employed to explain the lattice dimensional change during the irreversible red-to-blue chromatic transition of the metastable polydiacetylenic crystals.

A general, aerosol-based, one-step approach was explored to synthesize microporous and mesoporous spherical carbon particles with highly porous foam-like structures from aqueous sucrose solutions containing colloidal silica particles and/or silicate cluster templates.

Mesoporous silica is of great interest for many applications. [1,2] The past decade of research enables precise mesostructural control through tuning the co-assembly of surfactant and silicate. Functionalization of mesoporous silica, a process that imparts functionality to the pore surface or pore wall, is essential to convert the relatively inert silica into various functional materials. [3,4] Until now, functionalization of mesoporous silica has often been achieved by post-grafting methods, [5,6] direct-synthesis methods, [7,8] or by using functional surfactants.[9] The direct-synthesis method provides mesoporous silica with functionalities through co-assembly of surfactants with organosilane precursors that contain non-hydrolyzable pendant or bridged organic ligands. [6±8,10±13] Current research in this area has been focused on the synthesis of functionalized mesoporous silica with organic or metallic moieties. [3,14] This communication reports the synthesis of ordered mesoporous carbon/silica composites with unique pore walls that are composed of molecularly integrated silica and carbon. This is achieved by co-assembling octadecyltrimethylammonium bromide (OTAB) with 1,4-bis(triethoxysilyl)benzene (BTEB), [13] followed by a carbonization process that decomposes the surfactant and converts the phenylene moieties into carbon. The incorporation of carbon into the pore wall not only results in interesting mesoporous carbon/silica nanocomposites, but also may provide materials with improved thermal, chemical, and mechanical properties. Furthermore, removal of the silica from the carbon/silica nanocomposites results in mesoporous carbon materials that can positively replicate the mesostructure of the silica template. Compared with the conventional two-step synthesis of mesoporous carbon [15] in which mesoporous carbon (an inverse replica of silica) is prepared by the infiltration of carbon precursors into preformed mesoporous silica followed by carbonization and silica removal, this method provides a direct method to synthesize mesoporous carbon for hydrogen storage, catalysts, fuel cells, and other applications. Figure 1 shows the X-ray diffraction (XRD) patterns of the phenylene/silica/surfactant hybrid powders before the removal of surfactant (curve a), after the removal of surfactant by solvent extraction (curve b), and after the carbonization in N 2 at 900 C (curve c). Similar to previously reported results, [13] the phenylene/silica hybrid materials before and after surfactant removal exhibit typical low-angle diffraction peaks that correspond to a hexagonal mesostructure with a d 100 spacing of 4.8 nm. The high-angle diffraction peaks (curves a,b) demonstrate the periodic crystal-like structure COMMUNICATIONS 704

“Nano-onions” with multifold alternating CdS/CdSe or CdSe/CdS structure have been synthesized via a two-phase approach. The influences of shell on photoluminescence (PL) quantum yields (QYs) and PL lifetimes are investigated and discussed. It is found that the outmost shell plays an important role in the PL QYs and PL lifetimes of the multishells “onion-like” nanocrystals. The PL QYs and PL lifetimes fluctuate regularly with CdSe and CdS shells. The PL QY increases when the nanocrystals have an outmost CdS shell; however, it decreases dramatically with the outmost CdSe shell. The trend of the change of PL lifetimes is consistent with that of the QYs. The crystal structure and composition of the novel nano-onions are characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectra techniques.