Jaswinder Sharma

Synthesis of Segmented Silica Rods by Regulation of the Growth Temperature

The control of the diameter of colloidal structures is of fundamental interest and practical importance. We synthesized segmented silica rods by regulating the reaction temperature while the rods were growing. With higher growth temperatures, the segment diameter became smaller. Longer incubation times gave longer segments at the same temperature. Similarly, high temperature for the same incubation time gave longer segments. It appears that the correlation between temperature and diameter results from the relation between temperature and the size of the emulsion droplet, that is, the higher the temperature, the smaller the emulsion droplet.

Step-by-Step Growth of Complex Oxide Microstructures†

The synthesis of complex and hybrid oxide microstructures is of fundamental interest and practical applications. However, the design and synthesis of such structures is a challenging task. A solution-phase process to synthesize complex silica and silica-titania hybrid microstructures was developed by exploiting the emulsion-droplet-based step-by-step growth featuring shape control. The strategy is robust and can be extended to the preparation of complex hybrid structures consisting of two or more materials, with each having its own shape.

Addressable morphology control of silica structures by manipulating the reagent addition time

The current synthesis strategies focus on addition of all reagents together. Herein, we demonstrate the effect of reagent addition time on the final morphology of colloidal silica structures without changing the actual reaction conditions, and utilize this effect to synthesize silica rods with addressable diameter control.

Colloidosome like structures: self-assembly of silica microrods

Self-assembly of one-dimensional structures is attracting a great deal of interest because assembled structures can provide better properties compared to individual building blocks. In the present work, silica microrod self-assembly has been demonstrated by exploiting Pickering emulsion based strategy. Micron-sized silica rods were synthesized employing previously reported methods based on polyvinylpyrrolidone/pentanol emulsion droplets. Rods self-assembled to make structures in the range of ≈10–40 μm. Smooth rods assembled better than segmented rods. The assembled structures were bonded by weak van der Waals forces.

Synthesis of half sphere-half funnel shaped silica structures by reagent localization and the role of water in shape control

Shape control of silica structures is demonstrated by localization of the reagents. A uniform dispersion of reagents provided straight silica rods, whereas localization of the reagents in the emulsion droplet periphery provided a new type of half-sphere/half-funnel structure. The effect of water concentration appeared to be related to the ease of diffusion of the silica precursor inside the emulsion droplet (i.e., the higher the water concentration, the lower the silica precursor diffusion).

Effect of polymer residues on the electrical properties of large-area graphene–hexagonal boron nitride planar heterostructures

Polymer residue plays an important role in the performance of 2D heterostructured materials. Herein, we study the effect of polymer residual impurities on the electrical properties of graphene-boron nitride planar heterostructures. Large-area graphene (Gr) and hexagonal boron nitride (h-BN) monolayers were synthesized using chemical vapor deposition techniques. Atomic van-der-Waals heterostructure layers based on varied configurations of Gr and h-BN layers were assembled. The average interlayer resistance of the heterojunctions over a 1 cm2 area for several planar heterostructure configurations was assessed by impedance spectroscopy and modeled by equivalent electrical circuits. Conductive AFM measurements showed that the presence of polymer residues on the surface of the Gr and h-BN monolayers resulted in significant resistance deviations over nanoscale regions.

Development of a Long-Life-Cycle, Highly Water-Resistant Solar Reflective Retrofit Roof Coating

Highly water-resistant and solar-reflective coatings for low-slope roofs are potentially among the most economical retrofit approaches to thermal management of the building envelope. Therefore, they represent a key building technology research program within the Department of Energy. Research efforts in industry and the Department of Energy are currently under way to increase long-term solar reflectance on a number of fronts. These include new polymer coatings technologies to provide longer-lasting solar reflectivity and improved test methodologies to predict long-term soiling and microbial performance. The focus on long-term improvements in soiling and microbial resistance for maximum reflectance does not address the single most important factor impacting the long-term sustainability of low-slope roof coatings: excellent water resistance. The hydrophobic character of asphaltic roof products makes them uniquely suitable for water resistance, but their low albedo and poor exterior durability are disadvantages. A reflective coating that maintains very high water resistance with increased long-term resistance to soiling and microbial activity would provide additional energy savings and extend roof service life.