Characterization of nano‐organized multilayers constituted by successive inorganic (gold) and organic (alkylthiols) layers

Nanostructured multilayers constituted by alternate metallic (gold) and organic (alkyldithiol) layers, and grafted onto glass or silicon substrates are prepared and analysed. Such complex layers could be of interest as a new type of surfaces but also as localized dissipative zones particularly in the field of adhesion science. The formation and the structure of these model systems are examined using a number of techniques such as atomic force microscopy (AFM), wetting analysis (contact angles), X‐ray photoelectron spectroscopy (XPS) and conductivity measurements. It is shown that, in terms of electrical conductivity, gold layers exhibit a percolation transition from an insulating granular structure to a conductive worm‐like structure at a threshold thickness of about 5 nm. XPS (and wettability) analyses clearly indicate that the fractional coverage of the gold surface is about 30% with alkyldithiol and that these molecules are either grafted in a stand‐up position or in the form of a loop. Moreover, a partial electrical connection between two successive gold layers is observed, confirming that the confined organic layer of alkyldithiol between them is too loosely organized to play the role of an insulating barrier. Copyright © 2007 John Wiley & Sons, Ltd.     

Stability-indicating assay using capillary zone electrophoresis for an azaphenothiazine in an ointment formulation

A stability-indicating assay using a capillary zone electrophoresis method is reported for the determination of isothipendyl in an ointment formulation. Sample preparation consisted of a simple dissolution of the ointment in an internal standard (3-aminobenzoic acid hydrochloride) solution. Separation was carried out in a short fused silica capillary using a pH 2.5 phosphate buffer as electrolyte. After introduction of the sample solution into the capillary, the compounds were separated as cations and detected within 3 min. The procedure was validated following the guidelines of the International Conference on Harmonisation. The method was found to be specific in relation to potential degradation products and excipients. Linearity determined between 50 and 150% of the target concentration was satisfactory (r² = 0.999). Recovery studies from an analytical placebo spiked with the analyte at five concentration levels (50-150% of the target concentration) on each of 3 days ranged from 103.5 to 99.2%. The repeatability of the entire procedure (n = 7) was better than 1.0%. The detection limit was estimated to be approximately 0.5 mg l⁻¹.     

Electrical and physico-chemical properties of nanolayers of Conducting polyaniline-polystyrene or camphor sulfonic acid blends

In this work we studied the physico-chemical and electrical properties of conducting blends of polyaniline (PANI) with polystyrene (PS) or camphor sulfonic acid (CSA) in an appropriate solvent such as m-cresol using various concentrations of PS. The thin films or nanolayers prepared by spin coating were analysed by ellipsometry (to measure the thickness), dynamic contact angle (to measure the surface energy), atomic force micropsopy techniques (to observe the topography and roughness of films), and by using a Keithley SMU 236 recorder under a vacuum of 10⁻³ mbar, to determine the variation of the current as a function of the voltage. Results obtained show that the variations of current I versus of the voltage V (from −15 V to +15 V) for all samples coated on silicon substrate indicate a barrier effect that becomes more and more important with the increase of the PS content, while samples prepared on a glass substrate give a linear variation of the current according to the voltage. These observations (load space limited current, Fowler-Nordheim tunneling effect, light-emitting diodes) will be described in this paper. The electrical conductivity of the PANI-CSA-PS blends at room temperature for different concentrations of polystyrene (from 0% to 50%) was measured by the four probe method as a function of the PANI weight fraction x. It seems that when x increases the electrical conductivity σ increases and reaches a threshold for x = 0.5 and σ = 8.5 S/cm.