The computerized determination of double-layer capacitance with the use of kalousek-type waveforms and its application in titrimetry

A method for the rapid determination of double-layer capacitance—potential curves of electrodes is described. An on-line computer is used to apply Kalousek-type waveforms to the electrochemical cell and to measure the accompanying current response. The capacitances are determined from the slope of the plots of log current against time. For 0.1 M KCl, the computerized method agrees well with the bridge method, except for the potential range of 0 to –0.15 V. The method is very useful for automating titrations with tensammetric detection of the end-point. The method is applied to the titration of barium with a macrocydic compound (kryptofix 222) and the titration of cetyl-trimethyl-ammonium bromide with bromocresol purple. The accuracy of the titrations is ±2%

The catalytic activity of laccase immobilized onto free and surfactant modified silica aerogels

The free silica aerogel (FSA) and surfactant (cetyltrimethylammonium bromide) modified silica aerogel (MSA) were synthesized and used as supports for laccase immobilization carried out through adsorption process. The results show that the MSA performed higher laccase adsorption (0.71µmol/g) as compare to FSA (0.22µmol/g). In addition, the enhancement of the catalytic activity of the MSAL was also observed. These results demonstrated that the surface modification of silica aerogel using cationic surfactant (cetyltrimethylammonium bromide) gave higher immobilized mass and catalytic activity of laccase which can be potentially used for degradation of organic micropollutants such dyes, pesticides and antibiotics

Nonaqueous Fluoride/Chloride Anion-Promoted Delamination of Layered Zeolite Precursors: Synthesis and Characterization of UCB-2

The delamination of layered zeolite precursor PREFER is demonstrated under mild nonaqueous conditions using a mixture of cetyltrimethylammonium bromide, tetrabutylammonium fluoride, and tetrabutylammonium chloride in N,N-dimethylformamide (DMF) as solvent. The delamination proceeds through a swollen material intermediate which is characterized using powder X-ray diffraction (PXRD). Subsequent addition of concentrated HCl at room temperature leads to synthesis of UCB-2 via delamination of the swollen PREFER material and is characterized using PXRD, transmission electron microscopy (TEM), and argon gas physisorption, which shows lack of microporosity in UCB-2. ^(29)Si magic angle spinning (MAS) NMR spectroscopy indicates lack of amorphization during delamination, as indicated by the entire absence of Q^2 resonances, and ^(27)Al MAS NMR spectroscopy shows exclusively tetrahedral aluminum in the framework following delamination. The delamination process requires both chloride and fluoride anions and is sensitive to solvent, working well in DMF. Experiments aimed at synthesizing UCB-2 using aqueous conditions previously used for UCB-1 synthesis leads to partial swelling and lack of delamination upon acidification. A similar lack of delamination is observed upon attempting synthesis of UCB-1 under conditions used for UCB-2 synthesis. The delamination of PREFER is reversible between delaminated and swollen states in the following manner. Treatment of as-made UCB-2 with the same reagents as used here for the swelling of PREFER causes the delaminated UCB-2 material to revert back to swollen PREFER. This causes the delaminated UCB-2 material to revert back to swollen PREFER. Altogether, these results highlight delamination as the reverse of zeolite synthesis and demonstrate the crucial role of noncovalent self-assembly involving the zeolitic framework and cations/anions/structure-directing agent and solvent during the delamination process

Micellar region of ionic surfactant solution and its microenvironment properties

The conventional method which have been used most extensively to determine aggregation number, n such as classical and quasi-elastic light scattering suffers from the lack in the determination of n as a function of concentration. It has been proposed that a fluorescence method of micelle-solubilized pyrene and using the ratio of the first and third vibronic bands as an index of the effective local polarity, provides an alternative to the study of the microenvironment of micellar interior It is well understood that the addition of a third component, affects not only the critical micelle concentration, cmc and aggregation number but also the microenvironment of the micelle. Compounds such as alcohols which are solubilized in the micelles, directly modify the micelle itself. Addition of salts modifies the electric double layer around a micelle and alters the hydrophobic interaction, which is significant for micelle formation. The variations in the hydrophobic interaction indirectly influence the microenvironment inside the micelles. With that note, this work is directed to the investigation of the micellar region and the microenvironment property namely micropolarity, of micellar interior of two ionic surfactant, above emc, upon the addition of a medium chain alcohol, pentanol employing the fluorescence probing method. The ionic surfactants are the negatively charged, sodium dodecyI sulphate, SDS and the positively charged, cetyltrimethylammonium bromide, CTAB. From the phase diagram studies, the micellar region has been successfully constructed and identified in both aqueous and nonaqueous systems at 30˚C The results show that the presence of a polar solvent, glycerol disturbs the stability of the micellar region in both of the ionic surfactant systems. The result also show that the negatively charged, SDS is more superior in solubilizing pentanol than the positively charged, CTAB in the aqueous systems. From the fluorescence studies, the results show a decrease in the ratio of the vibronic bands at higher pentanol content. The micro polarity of the micellar interior with CT AB is, however, found to be higher than the corresponding one with SDS regardless of the concentration of the ionic surfactant solution. In addition, a transition in the micellar shape is also observed and is further supported by the conductivity studies

Interface instability in shear banding flow

We report on the spatio-temporal dynamics of the interface in shear-banding flow of a wormlike micellar system (cetyltrimethylammonium bromide and sodium nitrate in water) during a start-up experiment. Using the scattering properties of the induced structures, we demonstrate the existence of an instability of the interface between bands along the vorticity direction. Different regimes of spatio-temporal dynamics of the interface are indentified along the stress plateau. We build a model based on the flow symetry which qualitatively describes the observed patterns

Kinetics and mechanistic study of cetyltrimethylammonium bromide catalyzed oxidation of tetraethylene glycol by N-chlorosaccharin in acidic medium

The kinetics and mechanism of cetyltrimethylammonium bromide catalyzed oxidation of tetraethylene glycol [2,2'-(oxibis(ethylenoxy)diethanol)] by N-chlorosaccharin in aqueous acetic acid medium in presence of perchloric acid have been investigated at 323K. The reaction is first order dependence on Nchlorosaccharin. The reaction rate follows first order kinetics with respect to [tetraethylene glycol] with excess concentration of other reactants. The miceller effect due to cetyltrimethylammonium bromide, a cationic surfactant has been studied. The change in ionic strength shows negligible salt effect. The dielectric effect is found to be positive. Addition of one of the products (saccharin) retards the reaction rate. Activation parameters are calculated from the Arrhenious plot. A possible mechanism consistent with the experimental results has been proposed

Hierarchically structured biphenylene-bridged periodic mesoporous organosilica

Novel composites of highly ordered and stable biphenyl-bridged periodic mesoporous organosilica (PMO) materials confined within the pores of anodic alumina membranes (AAM) were successfully synthesized by evaporation-induced self-assembly (EISA). 4,40-Bis(triethoxysilyl)biphenyl (BTEBP) was used as a precursor in combination with the ionic surfactant cetyltrimethylammonium bromide (CTAB) or triblock-copolymer F127 as structure-directing agents. The resulting mesophases were characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). With ionic CTAB as a structure directing agent, samples with a mixture of the 2D-hexagonal columnar and a lamellar mesophase were obtained within the AAM channels. When using the nonionic surfactant F127, mesophases with a 2D-hexagonal circular structure were formed in the AAM channels. Additionally, a cubic Im3m phase could also be obtained with the same nonionic surfactant after the addition of lithium chloride to the precursor solution. The stability of both the circular and cubic biphenylene-bridged PMO against calcination temperatures of up to 250 °C was confirmed by NMR spectroscopy. Nitrogen sorption in the porous composite membrane shows typical type IV isotherms and narrow pore size distributions. All the biphenyl PMO/AAM composites show fluorescence due to the existence of biphenyl chromophores in the stable organosilica framework