Temperature and flow-induced viscosity transitions for CTAB surfactant solutions

We report in this work new results concerning the temperature dependence of the non-Newtonian viscosity of semi-diluted aqueous micellar solutions of cetyltrimethylammonium bromide (CTAB) in the presence of potassium bromide (KBr). Two structural transitions are responsible for the unusual flow curves obtained. The first transition induced by the shear flow corresponds to an induced liquid crystalline phase of the nematic type; the second corresponds to the disappearing of this phase with increase of the temperature.     

Linear and non linear rheology of a wormlike micellar system in presence of sodium tosylate

In this experimental work, we investigate the influence of an organic counterion, sodium tosylate, on the rheological properties of an aqueous solution of CTAB at the concentration of 0.05M. With this system we can clearly see shear thickening for small salt concentrations C _s and only shear thinning behavior at higher C _s characterized by a linear evolution of η=f(γ) in a log-log representation. In these evolutions it is only in a very small domain of concentrations of the salt (near C _s =0.035M) that we can observe a nearly constant plateau of the shear stress against shear rate. The values of σ₀ (characterizing the stress plateau), G ₀ (the plateau modulus) and τ_R (the relaxation time) obtained by dynamical rheological measurements, allow to compare experimental results obtained to predicted values of the theory of Cates corresponding to the occurrence of shear induced banding structures. Received: 22 July 1997 Accepted: 3 February 1998     

Improved optical performance of CdO films prepared with CTAB as surfactant

The influence of surfactant cetyl trimethyl ammonium bromide (CTAB) on structural, morphological and optical properties of CdO films has been investigated. Five series of CdO films were successfully prepared by successive ionic layer adsorption and reaction method with the assistance of CTAB. These CdO films were characterized by X-ray diffraction, scanning electron microscopy and UV–vis spectroscopy. The CTAB caused in a decrease in crystallite size but an increase in the optical band gap of CdO films. From the optical investigations, it was observed that the transmittance of the pure film was about 2% and it increased dramatically to 37% for 2?M% CTAB added CdO films at the wavelength of 1100?nm. The results show that the amount of CTAB played an important role in determining the physical properties of the CdO nanostructures.     

The Self-Association and Mixed Micellization of an Anionic Surfactant,Sodium Dodecyl Sulfate,and a Cationic Surfactant,Cetyltrimethylammonium Bromide: Conductometric,Dye Solubilization,and Surface Tension Studies

In the present study, we investigate the self-association and mixed micellization of an anionic surfactant, sodium dodecyl sulfate (SDS), and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The critical micelle concentration (CMC) of SDS, CTAB, and mixed (SDS + CTAB) surfactants was measured by electrical conductivity, dye solubilization, and surface tension measurements. The surface properties (viz., C₂₀ (the surfactant concentration required to reduce the surface tension by 20 mN/m), Π_CMC (the surface pressure at the CMC), Γ_max (maximum surface excess concentration at the air/water interface), and A_min (the minimum area per surfactant molecule at the air/water interface)) of SDS, CTAB, and (SDS + CTAB) micellar/mixed micellar systems were evaluated. The thermodynamic parameters of the micellar (SDS and CTAB), and mixed micellar (SDS + CTAB) systems were evaluated.

A schematic representation of micelles and mixed micelles.     

多壁碳纳米管/十六烷基三甲基溴化铵修饰丝印电极的制备及大鼠血中雌二醇水平的测定

制备了多壁碳纳米管-十六烷基三甲基溴化铵(MWCNTs/CTAB)修饰丝印电极(MWCNTs-CTAB/SPE),并将其应用于大鼠血样中雌二醇(E2)的测定。在优化条件下,应用方波伏安法测定E2的氧化峰电流的线性范围为5.0×10~(-10)~1.0×10~(-8) mol/L(R=0.9968),检测限为5.0×10~(-11) mol/L。大鼠注射外源性E2后,MWCNTs-CTAB/SPE能特异性地测定血样中的E2,该方法与放射免疫测定法(RIA)比较,MWCNTsCTAB/SPE测定步骤简单,具有较好的准确度、精密度以及稳定性。     

青霉素G钾盐在CTAB胶束中的水解及其抑制

以紫外光谱法研究了青霉素G钾盐(Pen-K)在十六烷基三甲基溴化铵（CTAB）胶束体系中的水解反应, 并探讨了水解反应机理.结果表明, CTAB胶束对Pen-K的水解具有抑制作用; Pen-K在CTAB胶束体系水解时,体系pH值的变化与在水中相似, 表明H＋浓度对这种抑制作用影响较小.红外光谱和微极性研究表明,部分Pen-K钾盐定位于CTAB胶束栅栏层中, 增加了其稳定性.     

Intrinsic Crosslinking and Gel-Breaking Rheokinetics of CMHEC/CTAB Systems

The intrinsic rheokinetics of carboxymethyl hydroxyethyl cellulose and cetyltrimethyl ammonium bromide (CMHEC/CTAB) synergistic fracturing fluid in static crosslinking and gel-breaking processes were studied in this work. Microrheological properties including solid–liquid balance (SLB) and elasticity index (EI) during the static crosslinking and gel-breaking processes were obtained. The effects of temperature on the crosslinking process, concentration of gel-breaker (ammonium persulfate), and temperature on the gel-breaking process were investigated. The novel intrinsic crosslinking and gel-breaking rheokinetics equations were established, respectively. The results show that the crosslinking process can be divided into two stages, and the intrinsic crosslinking rheokinetics equation can well describe EI curves during the static crosslinking process at different temperatures. The EI curves during the gel-breaking process can be well described by the intrinsic gel-breaking rheokinetics equation. The parameters for these two rheokinetics equations are well-defined and reasonable.     

Role of cetyltrimethylammonium bromide (cationic surfactant) on the tryptophan–MnO4 reaction

Upon addition of permanganate to a solution of tryptophan (Trp), yellow-brown color species appears within the time of mixing of tryptophan in absence and presence of cetyltrimethylammonium bromide (CTAB), which was stable for some days. Spectroscopic and kinetic evidences suggest the formation of water-soluble colloidal MnO₂ as the most stable reduction product of MnO₄⁻. Carbon dioxide and ammonia are not formed as the oxidation products. Carbon–carbon double bond of indole moiety of Trp is responsible for the fast reduction of permanganate. Cetyltrimethylammonium bromide catalyses the permanganate oxidation of Trp with a rate enhancement of ca. 200-fold. Sub- and postmicellar catalytic effect of CTAB ascribed to the association/incorporation/solubilization of both reactants (MnO₄⁻ and Trp) with the CTAB aggregates and into the Stern layer of cationic micelles. Quantitative kinetic analysis of the rate constant–[CTAB] data has been performed on the basis of modified pseudo-phase model of the micelles. A comparison was made of the oxidation rates of different amino acids by permanganate. The order of the effectiveness was as follows: tryptophan  tyrosine  phenylalanine.     

球状PbS纳米颗粒的室温合成与性能表征

以醋酸铅为铅源,硫代乙酰胺为硫源,在表面活性剂十二烷基硫酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)共同作用下,在常温下合成了PbS纳米晶,利用XRD、紫外分光度计、SEM、TEM对合成产物的结构和形貌以及光学特性进行了表征分析,结果表明,合成的PbS为尺寸均匀的球形纳米晶,对合成的PbS纳米晶的形成机理进行了初探.当反应温度较低时,形成的PbS小颗粒在表面活性剂SDS的烷基链模板和CTAB微胶束软模板共同作用下生成球状PbS纳米晶.     

孔雀绿与CTAB胶束的相互作用

以CTAB胶束模拟生命体系,用UV-Vis和荧光光谱等技术研究了孔雀绿与CTAB胶束的相互作用.结果表明,孔雀绿自发地定位于CTAB胶束栅栏层,使得胶束聚集数增加,胶束的微环境极性I1/I3下降.孔雀绿与CTAB胶束之间的结合常数K和孔雀绿在胶束相与水连续相之间的分配系数KD均随孔雀绿浓度增加而降低,表明孔雀绿与CTAB胶束之间的相互作用随孔雀绿浓度增加而降低.