Mmh Chowdhury

Schottky barrier and surface plasmonic resonance phenomena towards the photocatalytic reaction: study of their mechanisms to enhance photocatalytic activity

Metals are doped on semiconductors to enhance the activity of photocatalysts and two possible phenomena can happen at the interfaces of the semiconductors: Schottky barrier formation and Surface Plasmonic Resonance (SPR). Schottky barriers can improve the photoactivity of a reaction by trapping and prolonging the life of the electron. While SPR has the ability to create an electromagnetic field which can improve the photoreaction in three ways: photon scattering, Plasmon Resonance Energy Transfer (PRET) and hot electron excitation. Although both phenomena have been well grounded throughout the field, one crucial ambiguity is still found based on the proposed mechanisms, specifically, what is the direction of electron flow – from metal to semiconductor or vice versa? This feature article reviews the mechanism focusing on how Schottky barrier and SPR phenomena help to improve a photoreaction, as well as the paradox between the Schottky barrier and SPR in the matter of the direction of electron flow in the metal/semiconductor system.

Studies of Micromechanical Deformation Processes in Particle-Filled Glassy Polymer

ABSTRACT The deformation behavior of rubber-toughened polymer, which was prepared by incorporating soft, core-shell rubbery particles into a glassy polymer such as poly (methyl methacrylate) (PMMA), has been investigated by means of mechanical tests, optical monitoring (OM), and scanning electron microscopy (SEM). By mechanical testing, the neat PMMA reveals a 2% strain with high yield stress. After inclusion of 17.5 and 35 vol%rubber particles, the softened-PMMA samples exhibit corresponding strain of 20% and 38%, showing an increase of strain along with the relative decrease of yield stress, resulting in a toughening behavior of PMMA. Clear shear bands and stress whitening develop in the rubber-toughened PMMA after deformation, as observed by OM. Investigation by SEM shows crazes/cracks in the stretched, rubber-softened PMMA samples in which the core-shell particles are found to be cavitated. The mechanism of this deformation has been explained based on the void formation in the rubbery shell as well as the initiation and propagation of crazing.

Synthesis of Polyelectrolyte and Studies of its Conductivity Changes with Respect to Molecular Weight

Aqueous solutions of acrylamide monomer were irradiated by γ-rays using a Co-60 source to synthesize polyacrylamide of different molecular weight (Mw). Solubility tests together with ultraviolet and infrared spectroscopic studies were performed for examining the irradiated samples to ensure that the prepared products were gradually converted from monomer to polymer (polyacrylamide), depending on the radiation dose. Various physico-chemical properties like polymer conversion, gel content, viscosity, and molecular weight of the products were determined. The conversion of polymer from monomer is initiated at a dose of 0.06 kGy and completed at about 0.14 kGy. The gel point, which indicates a dose for the onset of a network polymer structure, is identified to be 0.15 kGy providing valuable information about γ-ray synthesis of polyacrylamides. Viscosity and molecular weight are found to increase with radiation dose. Since polyacrylamides exhibit polyelectrolytic behavior in aqueous solutions, studies on conductivity changes of polyelectrolytes with respect to Mw, which is the main issue of this investigation, also were performed. The equivalent conductance of polyelectrolyte solutions was found to decrease with the molecular weight of the synthesized polymer. This change of conducting property of the prepared samples is explained based on the theory of polyelectrolyte solutions.