AGGREGATION CHARACTERISTICS OF LASER DYE RHODAMINE 6G IN AQUEOUS SURFACTANT SOLUTIONS

Abstract— –The role of surfactants as deaggregating agents for the laser dyes is investigated by spectrophotometry using Rhodamine 6G as a representative. A method to estimate the fraction of dye present as monomer, dimer and as a monomer-surfactant (monomer or micelle) complex is described. It is shown that among the surfactants, cetyl trimethyl ammonium bromide, Triton X-100, sodium lauryl sulfate (SLS) and potassium oleate, the anionic ones are the most effective in suppressing the aggregation of Rhodamine 6G. While the non-ionic surfactant is found to be effective only above its critical micellar concentration, the cationic surfactant has no effect on aggregation. The optimum concentration of SLS needed for suppression of dye-dimers is estimated.     

A systematic scheme of qualitative analysis for anions. part I

A new and comprehensive scheme for the systematic detection of anions has been put forward. This scheme is based on the precipitation of difficultly soluble salts of anions in groups by basic group reagents in sodium carbonate solution and the subsequent analysis of cach group precipitate or filtrate for the detection of individual members of the group     

Chemically selective membrane optode for Cr(VI) determination in aqueous samples

A methodology for simultaneous preconcentration and determination of Cr(VI) from aqueous samples was developed using a membrane optode formed by physical inclusion of a Cr(VI) selective chromophore 1,5-diphenylcarbazide (DPC) into a plasticized cellulose triacetate matrix. The inclusion of an anion exchanger (Aliquat-336) was found to be effective for immobilization of both DPC and Cr(VI)-DPC complex in the optode matrix itself. The proportionality in intensity of the magenta color on the optodes loaded with varying amounts of Cr(VI) suggests its potential applications for screening of Cr(VI) in aqueous samples by visual colorimetry. On loading high amounts of Cr(VI) in the membrane optode, its color changes from magenta to yellow, which indicates the possibility of using it as a threshold detector for Cr(VI). The membrane optode was optimized in terms of obtaining maximum preconcentration efficiency for Cr(VI) and subsequent stable optical response proportional to the amount of Cr(VI) in the membrane optode sample. The membrane optodes were tested for Cr(VI) determination in tap water and seawater samples. Using this optode, Cr(VI) even at levels of 13.6 ppb could be quantitatively detected. The optodes developed in the present work were found to be stable, cost effective, easy to prepare and efficient for direct preconcentration and determination of Cr(VI) in a variety of aqueous samples using spectrophotometry. However, this membrane optode is for one time use only as the reaction of Cr(VI) with DPC is irreversible.     

Synthesis of 2‐Coumarinyl and Spiroindolyl‐5‐Phenyl‐1,3,4‐Oxadiazoles

The 2H‐1‐benzo/naphthopyran‐2‐one‐4‐yl (un)substituted phenyl‐1,3,4‐oxadiazoles has been synthesized by the oxidative cyclization of benzoic acid hydrazides formed in situ by the condensation of the respective 2H‐1‐benzo/naphthopyran‐2‐one‐4‐carboxaldehyde and (un)substituted monobenzoyl hydrazide in moderate yields. Also, spiro[indoline‐thiozolidine]‐2,4′‐diones has been syhthesized in a similar way from 3‐phenyl‐spiro[3H‐indoline‐3,2′‐thiozolidine]‐2,4′‐(1 H)dione monohydrazide and (un)substituted benzaldehydes.     

Inversion and structure formulae for a generalized Laplace transform

, D_v(.) , .     

Low-frequency static characterization of microstructures using acousto-optic modulated stroboscopic interferometer

Micro-electro-mechanical-systems (MEMS) structures such as microcantilevers, micromirrors, accelerometers, gyroscopes, and filters are some of the new types of integrated electro-mechanical microstructures in need of testing tools to measure precisely their static and dynamic properties. The acousto-optic-modulated-stroboscopic-interferometer (AOMSI) is an innovative tool that can be employed to investigate the above-mentioned characteristics for a given environmental condition. In this work, an optical non-contact system employing an acousto-optic-modulator (AOM) to conduct low frequency static characterization of MEMS microstructures is presented. The method is applied to a silicon-on-insulator (SOI) cantilever for demonstration purposes. The theoretical analysis is based on an energy approach. Experimental results are presented and compared with the theory, and are found to be in good agreement.     

The layer disorders defect in coir fiber under thermal and chemical treatment

Natural coir fibers, subjectd to thermal treatments in the range of 0°C to 200°C and alkali treatment with 5% to 30% concentration w/w, have been used in the present investigation to determine the interlayer variability of the cellulose planes (020), (110) and (1$ \bar 1 $ \bar 1 0). Among the equatorial reflections (110), (1$ \bar 1 $ \bar 1 0) and (020), the extent of variability is found to be more with the proportion of such affected planes less for (020) reflection in the native cellulose at lower temperature while at higher temperature (110) and (1$ \bar 1 $ \bar 1 0) become more affected by variability defect. (110) and (1$ \bar 1 $ \bar 1 0) planes are more affected also with alkali treatment.