Oxidoreduction of self-assembled monolayers (SAMs) of ferrocenyldodecanethiolate on gold in aqueous solutions of surface-active sodium n-alkyl sulfates (NaCnSO4) of 6, 8, 10, and 12 carbons is investigated by cyclic voltammetry and surface plasmon resonance. The effects of surfactant micellization and alkyl chain length on the redox response of the surface-tethered ferrocenes are examined. The SAM redox electrochemistry is sensitive to the surfactant aggregation state in solution. The nonideal behavior of the sodium alkyl sulfates at concentrations above the critical micelle concentration leads to a non-Nernstian variation of the SAM redox potential with concentration. The presence of micelles in solution results in decreased anodic-to-cathodic peak separations and anodic peak full widths at half-maximum. A longer alkyl chain length results in an increased ability of the alkyl sulfate anion to ion pair with the SAM-bound ferrocenium, resulting in oxidation of the ferrocene at lower potential. A comparison of the SAM redox potential at a fixed surfactant concentration of ideal behavior suggests a 4.5 × 10(4) difference in the ion-pairing abilities of the shorter-chain C6SO4(-) and longer-chain C12SO4(-). One-half of the available SAM-bound ferrocenes are oxidized in the NaCnSO4 electrolyte. Surfactant anions adsorb and assemble onto the SAM surface by specific ion-pairing interactions between the sulfate headgroups and oxidized ferrocenium species, forming an interdigitated monolayer in which the surfactant anions alternate between a heads-down and heads-up orientation with respect to the SAM. The work presented points to applications of ferrocenylalkanethiolate SAMs as anion-selective membranes, probes of micelle formation, and surfaces for the electrochemically switchable assembly of organosulfates.

The interfacial electrochemistry of self-assembled monolayers of ferrocenyldodecanethiolate on gold electrodes in aqueous solutions of the anionic surfactants sodium n-hexyl sulfate and sodium ndodecyl sulfate is reported. The effects of surfactant micellization and alkyl chain length on the redox potential of the monolayerbound ferrocene are examined. The non-ideal behavior of the sodium alkyl sulfate solution at concentrations above the critical micelle concentration leads to a non-Nernstian variation of the redox potential. A longer alkyl chain length results in an increased ion-pairing ability and the oxidation of the tethered ferrocene at lower potential.

Over the last decades, hydroxyapatite (HA) and its composite with biopolymer have been extensively developed and applied in biomedical application. The aim of this study is to produce a novel 3D porous HA scaffolds for bone tissue regeneration. Scaffolds with varying composition of HA, chitosan, gelatin, agarose and poly vinyl alcohol (PVA) were prepared using freeze drying method. The composite scaffold was analyzed to determine density, porosity, biodegradability, swelling kinetics, morphology and structural properties. Porosity and density of the prepared scaffolds were 85.17 to 92.21% and 0.317 to 0.495g/cm3, respectively. The swelling ability of the prepared scaffolds showed similar efficacy. FTIR analysis showed intermolecular interaction between components in the scaffold. Pore size of the developed scaffolds were measured by scanning electron microscopy and found that regardless of their composition showed adequate pore sizes ranging from 174 to 405µm. Brine shrimp lethality assay indicated that the obtained scaffolds had no cytotoxic effects, and that they had good biocompatibility. The results suggested that, these homogeneous composite scaffolds were found to be potential candidates as bone grafting materials for bone tissue engineering applications. On the other hand, polyvinyl alcohol, PVA, is a water soluble synthetic resin which is obtained through polymerization of vinyl acetate monomer. By hydrolysis, the acetate groups are converted in hydroxyl groups. The degree of hydrolysis in a polyvinyl alcohol reagent is controlled by this process. The polar nature of poly (vinyl alcohol) facilitates the formation of hydrogen bonds and eventual condensation with silanol groups (from developing polysilicate network) formed by hydrolysis of the silicon alkoxides. Keywords17 Moreover PVA has been proposed for controlled release systems and is employed in a variety of biomedical applications, generally being considered to be biocompatible. 18,19 A polymer or combination of polymers can be fabricated into a porous scaffold through various techniques, such as sintering, salt leaching, freeze-drying, solvent casting, gas foaming, fibre meshes, phase separation, melt moulding, emulsion free drying, solution casting, etc. Sintering uses high temperatures to bond substances together as well as burn out organic material to form a porous structure.20 Salt leaching is also feasible, but is limited by the prolonged contact of particles with water and the requirement for salt removal.21 This study has chosen freeze-drying because it can form highly a porous structure and offer stability and ease of handling. 22,23 This study focuses on preparing and characterizing composite scaffold synthesized from three natural-based materials-chitosan, gelatin and HA. Afterwards in combination with agarose/PVA, these three materials offer potential synergies between physical properties and bioactivity for use as bone substitutes in bone grafts, benefiting a range of surgical applications. So a well-designed three-dimensional ...

The previous studies on the petrophysical and volumetric analysis of Habiganj gas field were based on limited well data. As the accuracy of volumetric analysis relies greatly on petrophysical parameters, it is important to estimate them accurately. In this study we analyzed all eleven wells drilled in the Habiganj field to determine the petrophysical parameters. Analysis of the well logs revealed two distinct reservoir zones in this field termed as upper reservoir zone and lower reservoir zone. Stratigraphically, these two reservoir zones are in the Bokabil and Bhuban Formation of Surma Group. Petrophysical analysis shows significant differences between the two zones in terms of petrophysical parameters. Porosity in the upper reservoir zone ranges from 12% to 36%, with an average of 28%. This zone is highly permeable, as indicated by the average permeability of 500 mili Darcy (mD). The average water saturation in this zone is around 18% suggesting high gas saturation. The lower reservoir zone has an average porosity, permeability, and water saturation of 12%, 60mD, and 43%, respectively, indicating poor reservoir quality. An analysis of log motifs indicates that the upper reservoir zone is composed of stacked sands of blocky pattern. The sands in this interval are clean, as indicated by the lower shale volume of 12-15%. The average thickness of this zone is 230m, and the presence of this zone in all the drilled wells suggests high lateral continuity. The lower reservoir zone consists of sand bodies of serrated pattern. The sands have high shale volume and are laterally discontinuous. Overall, the upper reservoir zone has superior petrophysical properties to the lower reservoir zone. Although the reservoir quality of the lower reservoir zone is poorer than that of the upper zone, this zone can be considered as the secondary target for hydrocarbon production. Petrophysical parameters of this study were estimated from all the eleven wells drilled in this field; hence the values are more accurate. The reported values of the petrophysical parameters in this study are recommended to use to re-estimate the reserves in Habiganj field. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 10(1), 2021, P 1-10