Tuning the size and optical properties in molecular nano/microcrystals: manifestation of hierarchical interactions

Intermolecular interactions, such as hydrogen bonding, dipolar and van der Waals, occurring in molecular crystals cover a range of magnitudes. As the crystal evolves from a relatively softer state in the nanoscopic size regime to a harder one in the microcrystalline and bulk solid state, the impact of the hierarchy of intermolecular interactions can be expected to emerge in a progressive fashion. The strongest interactions alone would be manifested at small sizes; as the crystal grows, the effect of the weaker ones will be added on, with the bulk crystals exhibiting the cumulative impact of the different interactions. We demonstrate this phenomenon through investigations of the solution, colloid, and solid state of a novel zwitterionic molecule based on the diaminodicyanoquinodimethane framework. A reprecipitation-digestion protocol is developed for the fabrication of nano/microcrystals of varying sizes. Microscopic and spectroscopic characterizations reveal tuning of the size and optical properties of this material. The optical absorption of the colloidal particles evolves with size towards that of the bulk solid, the emission showing a steady enhancement of intensity. Crystallographic investigations coupled with semiempirical computations provide a viable model to describe the range of observations in terms of the gradual accumulation of hierarchical intermolecular interactions.     

Influence of Solids Concentration on the Isoelectric Point of Aqueous Barium Titanate

We report on findings that the particle surface charge is influenced by solids concentration in aqueous suspensions of BaTiO₃. Three decades in solids concentration were analyzed by combining results from two different electrokinetic methods. Combined results demonstrate a systematic acidic shift in the isoelectric pH with decreasing solids concentration. The shift is attributed to the development of a Ba-depleted, TiO₂-rich surface layer. Using kinetic arguments, it is shown that the thickness of this layer will be proportional to the surface-to-volume ratio.     

Thermally Driven Self‐Assembly of Nanomicelles: A Facile Route to Functional Monodisperse Mesoporous Colloidal Nanocomposites of Inorganic Nature and Mesoscale Size

Thermally driven self‐assembly of nanomicelles can be a feasible route to produce monodisperse porous colloidal nanocomposites of inorganic nature and sizes around the mesoscale (below 100 nm). Success relies on extending the lifetime of intermediate droplets (size below about 100 nm) that are obtained under particular conditions. Herein, the conditions for the long‐term stabilization of these unique templates are studied and a model proposed to produce monodisperse porous colloidal nanocomposites. As an example of the potential applications of this methodology, functional colloidal nanocomposites with a high loading of the doping material (30 mol%) are obtained. In particular, superparamagnetic nanomagnets of metallic nature encapsulated in porous oxide colloidal matrixes of mesoscale size that easily respond to an external magnetic field are prepared and characterized in terms of structure and textural and magnetic properties.     

Nanocomposites of styrene–butadiene rubber and synthetic anatase obtained by a colloidal route and their photooxidation

Photodegradable styrene–butadiene rubber (SBR)/TiO₂ nanocomposites were prepared by a colloidal route through the simple mixing of a commercial polymer latex and synthetic anatase nanoparticles. Stable colloids of pure anatase TiO₂ nanoparticles with an average diameter of 7 nm were prepared by a solvothermal route from the hydrolysis of titanium alkoxide by hydrogen peroxide in the presence of oleic acid. The photocatalytic degradation of the SBR–TiO₂ nanocomposites was carried out in ambient air at room temperature under a UV lamp and was monitored by Fourier transform infrared and UV–visible spectroscopies and differential scanning calorimetry. The results show that the SBR–TiO₂ nanocomposites were photocatalytically degraded under UV light, which indicate that the butadiene chains in the nanocomposite were oxidized during UV irradiation. Thermal analysis measurements indicated that crosslinking reactions occurred. The presence of anatase TiO₂ nanoparticles was found to accelerate the photocatalytic process, and the degradation mechanism was similar to that of the pure SBR polymer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Building Reconfigurable Devices Using Complex Liquid–Fluid Interfaces

Liquid–fluid interfaces provide a platform both for structuring liquids into complex shapes and assembling dimensionally confined, functional nanomaterials. Historically, attention in this area has focused on simple emulsions and foams, in which surface‐active materials such as surfactants or colloids stabilize structures against coalescence and alter the mechanical properties of the interface. In recent decades, however, a growing body of work has begun to demonstrate the full potential of the assembly of nanomaterials at liquid–fluid interfaces to generate functionally advanced, biomimetic systems. Here, a broad overview is given, from fundamentals to applications, of the use of liquid–fluid interfaces to generate complex, all‐liquid devices with a myriad of potential applications.     

Crystallization Kinetics and Morphology Control of Formamidinium–Cesium Mixed‐Cation Lead Mixed‐Halide Perovskite via Tunability of the Colloidal Precursor Solution

The meteoric rise of the field of perovskite solar cells has been fueled by the ease with which a wide range of high‐quality materials can be fabricated via simple solution processing methods. However, to date, little effort has been devoted to understanding the precursor solutions, and the role of additives such as hydrohalic acids upon film crystallization and final optoelectronic quality. Here, a direct link between the colloids concentration present in the [HC(NH₂)₂]_0.83Cs_0.17Pb(Br_0.2I_0.8)₃ precursor solution and the nucleation and growth stages of the thin film formation is established. Using dynamic light scattering analysis, the dissolution of colloids over a time span triggered by the addition of hydrohalic acids is monitored. These colloids appear to provide nucleation sites for the perovskite crystallization, which critically impacts morphology, crystal quality, and optoelectronic properties. Via 2D X‐ray diffraction, highly ordered and textured crystals for films prepared from solutions with lower colloidal concentrations are observed. This increase in material quality allows for a reduction in microstrain along with a twofold increase in charge‐carrier mobilities leading to values exceeding 20 cm² V^?1 s^?1. Using a solution with an optimized colloidal concentration, devices that reach current–voltage measured power conversion efficiency of 18.8% and stabilized efficiency of 17.9% are fabricated.