Md. Abu Bin Hasan Susan

Water Structure Modification by Sugars and Its Consequence on Micellization Behavior of Cetyltrimethylammonium Bromide in Aqueous Solution

Water structure modification by sugars with a wide difference in stereoregular structures ranging from monosaccharide to trisaccharide and its consequence on the micellization behavior of cetyltrimethylammonium bromide (CTAB) in aqueous medium have been investigated. The characteristic variation in water absorption peaks in the presence of d(−)fructose has been studied by near-infrared spectroscopy. The analyses show that the hydrogen bonding capability of d(+)glucose, d(−)fructose, sucrose, trehalose and raffinose is mainly responsible for the variation in water-additive interactions. The critical micelle concentration determined by specific conductivity measurement and aggregation number determined by steady state fluorescence quenching method show significant variations in presence of additives for CTAB in aqueous solution. The sugars interact with the water structure to varying extents owing to differences in hydrogen bonding capability depending on the stereoregularity of the structure. This induces differences in the microenvironment for competition between the hydrophobic interaction and degree of hydration of the hydrophilic group of the surfactant to ultimately influence the micellization behavior in aqueous solution.

An approach towards the synthesis and characterization of ZnO@Ag core@shell nanoparticles in water-in-oil microemulsion

Water-in-oil microemulsions have been found to be good templates and suitable media for the synthesis of ZnO and ZnO@Ag nanoparticles offering themselves as ideal ‘nanoreactors’ for uniform fabrication of core@shell nanoparticles.

Temperature perturbed water structure modification by D(−)-fructose at different concentrations

Temperature dependence of water structure modification has been studied at different D(−)-fructose concentrations by near-infrared (NIR) spectroscopy. The temperature susceptibility of different structural components of water with varying hydrogen bond strength in the presence of D(−)-fructose has also been investigated as a function of temperature by 2D correlation spectroscopy from the characteristic spectral variation in water absorption peaks. Apparent molar volume, limiting partial molar volume, free energy change of activation, change in enthalpy of activation and entropy of activation for viscous flow, and other thermodynamic parameters for aqueous solution of D(−)-fructose at different temperatures and concentrations correlate very well with the water structure modification and ordering in the presence of D(−)-fructose inferred from the results of NIR spectroscopy. A comprehensive analysis indicates that the hydrogen bonding capability of the axial and equatorial OH groups in D(−)-fructose varies to a large extent and is mainly responsible for water–fructose interactions with water clusters of different size and geometry such as, dimer, trimer, and cyclic chains at different D(−)-fructose concentrations. D(−)-fructose has been found to act as a water structure-breaker at lower concentrations whereas at higher concentrations it promotes water structure as a structure-maker additive.

Molecular level interactions in binary mixtures of 1-ethyl 3-methylimidazolium tetrafluoroborate and water

In this study, structures of different water species present in binary mixtures of an ionic liquid (IL), 1-ethyl 3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and water of varying compositions have been investigated by near-infrared (NIR) spectroscopy and for the first time aggregation behavior and interactions between different species in the system have been inferred from the analyses of combination bands of NIR spectra. The relative population of different water species as well as the strength of hydrogen bonding was obtained from the analyses of peak area and peak positions of the deconvoluted –OH band of water, respectively. The ratio of the population of associated water to the population of water species bonded to IL increases sharply with increasing mole fraction of IL at XIL > 0.40. Consequently, the excess molar volume vs. XIL profile of the mixtures passes through a maximum. For the water species bonded to IL, analysis of the peak position showed that the strength of hydrogen bonding shows a maximum suggesting the formation of two different types of aggregates of IL below and above XIL ≈ 0.26. The DLS measurements show that in the water-rich region of the binary systems, aggregates with hydrodynamic diameter of 354–590 nm are formed. The size of the aggregates has been found to increase with increasing amount of IL and decrease with increasing temperature. Finally, the properties of the IL–water binary mixtures have been found to be governed by the strength of IL–water bonds and population of IL–IL and water–water clusters.

Dynamic Percolation and Swollen Behavior of Nanodroplets in 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate/Triton X-100/Cyclohexane Microemulsions

Microemulsions comprising an ionic liquid (IL), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([emim][OTf]), as the polar component, Triton X-100 as a surfactant, and cyclohexane as the nonpolar medium were prepared and characterized. Conductivity and dynamic viscosity data were critically analyzed to confirm dynamic percolation among the droplets that are in continuous motion, aggregation, and fission. The transition from oil-continuous phase to bicontinuous phase was observed at the conductance and viscosity percolation thresholds and sharp changes in the values of conductivity and dynamic viscosity could be identified. Dynamic light scattering measurements revealed swelling of the droplets, which varied within the hydrodynamic diameter range of 10-100 nm. Diffusivity of the droplets suggested less Brownian movement with increased amount of the IL. Moreover, changes in the droplet sizes and diffusivity with increase in IL content supported dynamic percolation within the systems.

Effect of temperature perturbation on hydrogen bonding in aqueous solutions of different urea concentrations

Water absorption peaks in near-infrared (NIR) and attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectra at different temperatures both in the absence and presence of urea have been analyzed to investigate hydrogen bonding in aqueous solution by perturbing the temperature and concentration of urea. Concentration-dependent basic spectra of aqueous urea solutions represent different clusters in the system originating from the different extent of self-aggregation of urea molecules and water–urea interactions. Derivative and deconvoluted spectra confirm the presence of different structural components or clusters in pure water, but in the presence of urea a new strong water cluster could be identified for the first time above a certain concentration of urea. The degree of perturbation has been evaluated by 2D correlation and difference spectroscopy. The apparent molar volume, free energy change of activation (ΔG), change in enthalpy of activation (ΔH) and change in entropy of activation (ΔS) for the viscous flow of water in the presence and absence of urea have been analyzed. The comprehensive analyses help to infer the different extent of aggregation of the urea molecules and formation of clusters by water–urea interactions in aqueous urea solutions.

Metal Chalcogenide Nanocrystalline Solid Thin Films

Over the past decades, chemical bath deposition (CBD) has proven its suitability and has established itself as one of the prominent techniques for depositing different metal chalcogenide semiconductor thin films via ion-by-ion or by adsorption of colloidal particles from the chemical bath on the substrate. It is a simple, cost-effective and convenient method for large-scale deposition and has recently received a surge of interest. This article reviews the research progress in various methods or techniques including CBD for the preparation and study of the properties of metal chalcogenides. Various parameters for efficient preparation and variation in structural, morphological, compositional, optical properties, etc. are also briefly discussed.

Electrochemical Behavior of Malachite Green in Aqueous Solutions of Ionic Surfactants

Electrochemical behavior of malachite green (MG) oxalate in aqueous solution was studied in the presence of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), and an anionic surfactant, sodium dodecyl sulfate (SDS) at a glassy carbon electrode using cyclic voltammetry. The electrochemical oxidation of MG has been characterized as an electrochemically irreversible diffusion-controlled process. Oxidative peak current sharply decreased with increasing SDS concentration, while a slight increase with increasing [CTAB] was apparent. The apparent diffusion coefficient, the surface reaction rate constant, and the electron transfer coefficient of MG clearly show correlation of the electrochemical behavior with the dissolved states of the surfactants. Electrochemical observations together with spectrophotometric results at varying surfactant concentrations provide evidence of interaction of MG with the surfactants to varying extent depending on the type of the surfactant and the concentration.

Electrodeposition of cobalt with tunable morphology from reverse micellar solution

Electrodeposition of cobalt on a copper electrode was successfully performed from aqueous and reverse micellar solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), using constant potential electrolysis method. The potential to be applied for electrodeposition was judged from the cyclic voltammetric behavior of cobalt(II) in aqueous and reverse micellar solutions of CTAB at different compositions. The morphology, dimension, and crystallinity of cobalt deposited onto a copper substrate were evaluated from scanning electron microscopy (SEM) images and X-ray diffraction technique. The cobalt deposited on copper from aqueous solution does not show any definite shape and size, while the deposition from reverse micellar solutions occurred with definite shapes such as star-, flower-, and nanorod-like structures depending on the composition. The slow kinetics governed by the reverse micelles associated with the deposition brings about oriented growth of cobalt onto the copper substrate and offers the potential to electrochemically tune cobalt deposit with desirable morphology.

Potentiodynamic studies on corrosion of copper by chloride ions and its inhibition by inorganic and organic ions in aqueous buffer solution

Electrochemical oxidation of copper in aqueous phosphate buffer solution leads to the formation of passive films, which breakdown in the presence of aggressive chloride (Cl−) ions. The addition of Cl− ions in the medium causes shift in current and potential for both cathodic and anodic peaks. At low Cl− ion concentrations, the corrosion current is greatly enhanced and continues to increase up to a certain concentration, after which it decreases. The effect of inorganic ions, chromate (CrO42−) and tungstate (WO42−), and organic ions, acetate (CH3COO−) and oxalate (C2O42−), on the formation and breakdown of passive films in aqueous buffer solution containing 0.10 M Cl− ions have also been investigated. All of the ions inhibit corrosion of copper in the presence of aggressive Cl− ions following the order of overall inhibition efficiency of CrO42− > C2O42− > WO42− > CH3COO− under the experimental conditions.