Jacob George

Formation of periodic precipitation patterns: a moving boundary problem

A new scenario for the formation of Liesegang patterns is proposed. The periodic precipitation pattern formation in a gel column is interpreted as a moving boundary problem. The existing time law, space law, and width law are revisited and reformulated on the basis of a moving boundary assumption and more meaningful explanations are given. All the new equations suggested were found to be in good agreement with experimental observations.

Crystallization and structural properties of calcium malonate hydrate

Calcium malonate hydrate crystals were grown by the reaction method, with the aid of hydrosilica gel. Colourless and prismatic crystals up to 4.5 mm in size were obtained. Structural properties of the material were explored by employing X-ray diffraction (XRD), infrared (IR) absorption, laser Raman (LR), and thermogravimetric (TG) techniques. The IR spectrum indicates the presence of inequivalent water molecules in the structure of the compound. The thermal decomposition pattern of the sample suggests a three-stage decay scheme. About one-fifth of the weight is due to the presence of water of crystallization. The differential scanning calorimetric (DSC) study corroborates the presence of inequivalent water molecules in the structure.

Rhythmic pattern formations in gels and Matalon-Packter law: A fresh perspective

The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law, spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure on the initial concentrations of the reactants is derived. Matalon—Packter law, which relates the spacing coefficient with the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems

Pattern Formation in Reaction Diffusion Systems: A Moving Boundary Model

Periodic precipitation pattern formation in reaction diffusion systems is interpreted as a moving boundary problem. All the existing laws are reexamined on the basis of the moving boundary assumption. Experimental observations were found to be in good agreement with the new equations suggested.

Structural and plasmonic studies of Ag nanoparticles in silica glass hosts

Silica glassy materials doped with Ag were prepared through sol gel route. The structural studies of the prepared samples showed an icosahedral morphology of the nanocrystals formed along with spherical morphology. The XRD and TEM data confirmed the formation of silver nanoparticles of size between 20 and 22nm. The surface plasmon resonance (SPR) of silver nanoparticles with spherical morphology was studied with the discrete dipole approximation . The shape and size effects of the nanoparticles can induce distinctive features of the SPR spectrum. It has been shown that such effects can induce peak intensity enhancement, wavelength shift and spectral broadening of the SPR spectra of the nanoparticles. The results obtained depend on the existence of highly localized plasmonic oscillations. An attempt has also been made to calculate the van der Waals force between nanoparticles.