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电导率是研究水溶液中离子型表面活性剂胶束化行为的重要方法,本文总结了这个灵敏测定技术,分别着重讨论了两个重要特征参数(临界胶束浓度(cmc)和胶束的反离子解离度(α))的提取方法、电导率曲线某些特殊情况的分析以及预胶束化行为的研究,这对运用电导率技术研究当前不断增多的具有强分子间相互作用的表面活性剂(例如Geminis)体系具有参考价值. 相似文献
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采用电导法研究了不同温度下含酯基Gemini表面活性剂在纯水和在质量分数为10%的甲醇-水(MAWR),乙二醇-水(EG-WR),丙三醇-水(GL-WR)四种体系中的集聚行为和胶束热力学;聚集行为参数包括临界胶束浓度(cmc)和抗衡离子的解离程度(α)以及胶束的热力学参数,包括标准吉布斯自由能(ΔG_m~o)、吉布斯迁移自由能(ΔG_(trans)~o)、吉布斯烷基链胶束化自由能(ΔG_(tail)~o)、标准焓变(ΔH_m~o)和标准熵变(ΔS_m~o),均被计算和讨论。研究表明在所有的研究体系中,cmc值随着疏水链的增加而减小,随着加入的醇结构中羟基数目的增加而增大,随温度的升高先变小,后变大呈U字形;胶束化过程都是自发进行的,并且在293.15 K下,胶束化过程是吸热的,在293.15 K上,胶束化过程是放热的;通过稳态荧光光谱法研究了表面活性剂在纯水、有机醇-水混合溶液中的微极性,结果表明,在相同溶剂中,随着烷基链长度的增加,溶液微环境的疏水性越强;对于相同的Gemini表面活性剂,随着加入含羟基数目越多的醇,其微环境的疏水性越强。并研究了Gemini表面活性剂在混合体系中形成胶束过程的焓-熵补偿曲线。 相似文献
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本文通过等温滴定量热法(ITC)、电导法和浊度法研究了阴离子生物表面活性剂脱氧胆酸钠(NaDC)及其与相反电荷的十二烷基三甲基溴化铵(DTAB)在水溶液中的自组装热力学.ITC结果支持了NaDC在水溶液中先生成预胶束再形成稳定胶束的分步聚集模型,由此得到了NaDC的预胶束和胶束化过程的一系列热力学参数,并讨论了它们形成的热力学机理.进一步研究了具有头-尾链式和疏水-亲水刚性面式非对称结构的DTAB/NaDC混合体系的聚集热力学行为,得到了富NaDC临界混合胶束浓度(cmcmix)、富DTAB临界胶束浓度(CM)及对应过程的转变焓.结果表明,NaDC面式结构与DTAB链式结构的对称性差异以及相反电荷的相互作用,导致混合体系有别于单一表面活性剂或头-尾链式结构的混合体系的聚集行为.混合溶液的聚集行为受控于表面活性剂浓度和摩尔分数的变化.富NaDC胶束化过程为熵驱动,而富DTAB的两种胶束形态转变过程为熵焓共同驱动的热力学机理.这些结果对于从热力学角度认识胆汁酸盐的自组装机理以及与传统的头-尾链式结构的表面活性剂相互作用机理和相行为有重要的意义. 相似文献
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我们曾研究了黑皂膜的界面性质,为深入了解pH对偶氮苯类化合物在水溶液中及胶束表面上结构变化的影响,本文选用亮黄(BY)为谱学探针,仔细考察了其水溶液及溴化十六烷基三甲铵(CTAB)胶束溶液的共振Raman光谱,根据谱带指认,描述了由酸碱性导致的BY分子的结构变化,其中包括共振体间平衡和酸碱平衡。 相似文献
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用温度跃升快速反应动力学测试仪器,研究了合成表面活性剂SDS胶束水溶液体系与生物表面活性剂脱氧胆酸钠(NaDC)胶束水溶液体系中,金属离子Ni~(2+)-2,2′-Bipyridine(Bipy)络合物形成的动力学。实验结果表明,生物表面活性剂同样表现出程度不同的胶束催化作用。又采用假相模型处理SDS胶束体系中上述反应的动力学,由动力学结果计算出可供发生反应的胶束体积。结果表明,此体积比不加电解质的胶束溶液中的反应体积增大,此现象被认为是由无机电解质的存在所造成。 相似文献
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CTAB胶束微环境中BY增溶位置的探讨 总被引:7,自引:1,他引:7
本文用UV吸收光谱对(BY=CTAB)体系胶束化过程中预胶束的形成,以及预胶束向胶束的转变过程进行了分析。采用Gouy-Chapman模型,建立了CTAB胶束微环境中BY表现解离常数与胶束结构参数之间的定量关系,根据水溶液和各种盐浓度条件下CTAB胶束溶液中酸碱解离常数的测量,分析了BY在CTAB胶束扩散层中的增溶位置,讨论了CTAB胶束对BY选择性吸附的特性。 相似文献
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阳离子Gemini表面活性剂3,5-双(亚甲基十八烷基二甲基溴化铵)-1,2,4-三氮唑胶束对酯碱性水解的影响 总被引:1,自引:0,他引:1
在25℃条件下,研究了乙酸乙酯和乙酸戊酯在阳离子Gemini表面活性剂3,5—双(亚甲基十八烷基二甲基溴化铵)—1,2,4—三氮唑(简称18—triazole—18)胶束中的碱性水解反应。实验结果表明.在一定的表面活性剂浓度范围内,乙酸乙酯和乙酸戊酯在Gemini表面活性剂18—triazole—18胶束溶液中的碱性水解反应速率随表面活性剂浓度的增加呈上升趋势,达到一最大值后,随着浓度的增加呈下降趋势。实验结果还表明,18—triazole—18对乙酸乙酯碱性水解的影响较对乙酸戊酯碱性水解的影响大。随着底物疏水性的增加,乙酸乙酯和乙酸戊酯的碱性水解速率在18—triazole—18胶束中表观反应速率常数最大值分别为无表面活性剂时的5.5倍和1.1倍。 相似文献
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Brownian dynamics simulations for a coarse-grained model have been performed to study the formation of micelles from bile salts and mixed micelles with dipalmitoyl-phosphatidylcholine (DPPC) in aqueous solutions. The particular association behavior of bile salts as facial surfactants was shown to be caused by their special molecular architecture with a hydrophilic and a hydrophobic side. The experimentally observed smooth transition into the micellar region with increasing concentration is reproduced. Micelle size distributions have been evaluated at different bile salt concentrations. Typical structures of pure bile salt micelles could be identified. The composition and the structure of mixed micelles have been studied in their dependence on the bile salt/lipid concentration ratio in the aqueous solution. We have found that the bile salt fraction in the mixed micelles increases considerably with increasing bile salt/lipid concentration ratio and decreasing micelle size. The structural and thermodynamic features of micelle formation in the aqueous bile salt solutions with DPPC, which we have studied with the coarse-grained model, are in good qualitative agreement with experimental findings. 相似文献
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Takeda M Kusano T Matsunaga T Endo H Shibayama M Shikata T 《Langmuir : the ACS journal of surfaces and colloids》2011,27(5):1731-1738
Shear-induced thickening/thinning phenomena of aqueous rodlike micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium p-toluene sulfonate (NapTS) were investigated by means of simultaneous measurements of rheology and small-angle neutron scattering (SANS), the so-called Rheo-SANS. The aqueous CTAB/NapTS solutions were classified into five different categories dependent on their flow behavior and micellar structure. By increasing salt concentration and/or shear rates, the micelles underwent morphological transition from (i) spherical or short rodlike micelles to (ii) long rodlike micelles without entanglements, followed by (iii) those with entanglements. These transitions were recognized as changes in flow behavior from Newtonian to shear-thickening and shear-thinning flow, respectively. In the latter two cases, anisotropic SANS patterns appeared around these critical shear rates. The physical meaning of the anisotropic SANS patterns accompanied by shear-thickening flow behavior is discussed in conjunction with other shear-thickening systems. 相似文献
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M. Anamul Haque M. Muhibur Rahman M. Abu Bin Hasan Susan 《Journal of solution chemistry》2012,41(3):447-457
The electrochemical behavior of an anthraquinone (AQ) was studied in aqueous solutions at a glassy carbon electrode, using
the sodium salt of anthraquinone-2-sulfonic acid (AQS), by employing cyclic voltammetry. AQ undergoes a two-electron reduction
in aqueous media. The electrochemical behavior of AQ was also investigated in micelles, reverse micelles (CTAB/1-butanol/water),
and microemulsions (CTAB/1-butanol/water/cyclohexane) of cetyltrimethylammonium bromide (CTAB). The electrode reactions of
AQ in reverse micelles and microemulsions are nearly reversible at low oil (cyclohexane) content. However, at higher oil content,
the reversibility is gradually lost. In the case of reverse micelles, the reduction current, as well as the reduction potential,
of AQ depend on the transition from a micellar solution to a stable solution of reverse micelles that occurs with added 1-butanol.
In microemulsions, the change in cyclohexane content was found to cause a linear increase in the peak current for AQ reduction
as well as a linear decrease in the corresponding reduction potential. As the cyclohexane content is increased, the o/w microemulsions
dominated by micelles undergo a transition to a w/o microemulsion dominated by reverse micelles, which causes changes in the
electrochemical behavior. 相似文献
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Irina S. Ryzhkina Tat'yana N. Pashirova Wolf D. Habicher Ludmila A. Kudryavtseva Alexander I. Konovalov 《Macromolecular Symposia》2004,210(1):41-48
The formation of mixed micelles of amphiphilic calix[4]resorcinarenes with aminomethyl (AMC, PAMC), tris(hydroxymethyl)amide (THAC) fragments and the cationic surfactant cetyl trimethylammonium bromide (CTAB) in water and aqueous DMF solutions (10-50% DMF) leads to the decrease of the critical micelle concentration of the systems and the increase of the size of the mixed micelles in comparison with CTAB micelles. The catalytic activity of the mixed systems in the hydrolysis of phosphorus acid esters is higher than those of CTAB micelle and AMC, PAMC or THAC aggregates. 相似文献
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U. Costas-Costas C. Bravo-Díaz H. Chaimovich I.M. Cuccovia 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):385-394
The widespread use of toxic phosphates and phosphonates as insecticides, and their use as chemical weapons, has led to investigation of fast detoxification and decontamination methods. Micelles, microemulsions, cyclodextrines and liposomes have been used to accelerate phosphate ester decomposition by nucleophiles. Here, hydrolysis, methanolysis and hexanolysis of Tris-p-nitrophenyl phosphate (TNPP), a model for reactive phosphate esters, were studied in homogeneous phase, aqueous and reverse micelles. Kinetic micellar effects were quantitatively analyzed using pseudo-phase models. TNPP hydrolysis was catalyzed by cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium bromide (CTAB), and hexadecylammonium propanesulfonate (HPS), micelles by factors of five, CTAC, and three, CTAB, HPS, respectively. The calculated rate constants for spontaneous and acetate-catalyzed hydrolysis in the micellar phase were significantly higher than those in the aqueous phase. While in water and in methanol the effect of the acetate cation was negligible, the catalytic efficiency of acetate for hexanolysis depended on the nature of the cation with the K+ salt being ca. 20 times more efficient than the tetraethylammonium salt in non-polar solvents. Sodium dodecylsulfate, SDS, micelles inhibited TNPP hydrolysis by a factor of eigth. Reverse micelles of CTAB in n-hexanol/isooctane (10:90, v/v) did not catalyze TNPP hydrolysis, but changed the bis-p-nitrophenyl phosphate/hexyl-bis-p-nitrophenylphosphate product ratio depending of CTAB concentration and water/detergent ratio. 相似文献
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In a series of experiments, we studied the dynamic properties of aqueous surfactant solutions of cetyltrimethylammonium bromide (CTAB) at conditions after adding different amounts of sodium salicylate (NaSal). The aggregates, present in these solutions, are elongated, wormlike micelles, which tend to form entanglement networks. The viscoelastic, gel-like samples were analyzed by means of static, dynamic, and electrophoretic light scattering techniques. We separately investigated the effects of surfactant concentration and added salt on intermicellar interactions. The electrostatic interactions between the anisometric micelles were analyzed by considering the effective dimensions of the aggregates. We calculated the Debye-Huckel lengths from experimental data of the osmotic second virial coefficient and from the diffusion second virial coefficient. It turned out that the results were in good agreement with theoretically estimated values. We also measured the zeta potential and intensity of scattered light in a large range of different salt concentrations keeping the CTAB concentration constant. We observed an isoelectric point and charge reversal of the threadlike micelles at an excess salicylate concentration of about 100 mM. The observed decrease of the zeta potential points to striking processes of counterion condensation. In these solutions, the salicylate ion acts as a cosurfactant, due to its discrepancy between polar and hydrophobic groups. We also detected a simple linear correlation between the zeta potentials and the Debye screening lengths of the surfactant solutions. 相似文献
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We have compared micelles, reverse micelles, and reverse micelles encapsulating myoglobin using electrospray mass spectrometry. To enable a direct comparison, the same surfactant (cetyltrimethylammonium bromide (CTAB)) was used in each case and micelle formation was controlled by manipulating the aqueous and organic phases. Tandem mass spectra of the resulting micelle preparations reveal differences in the ions that dissociate: those that dissociate from regular micelles have undergone >90% exchange of bromide ions from the headgroup with acetate ions from bulk solvent. By contrast, for reverse micelles, ions are detected without exchange of bromide ions from the headgroup, consistent with their protection in the core of the micellar structure. Tandem mass spectra of micelles and reverse micelles reveal polydispersed assemblies containing several hundred CTAB molecules, indicating the coalescence of the micellar systems to form large assemblies. For reverse micelles incorporating myoglobin, spectra are consistent with one holo myogolobin molecule in association with approximately 270 CTAB molecules. Overall, therefore, our results show that the solution-phase orientation of surfactants is preserved during electrospray and are consistent with interactions being maintained between surfactants and an encapsulated protein. 相似文献
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Jamil K. J. Salem Hassan Tamous Fawzi Qudeh 《Journal of Dispersion Science and Technology》2013,34(4):563-567
Decomposition of monochloramines derived from amino acids were studied in buffer solution pH=7 in the presence of different concentrations of CTAB micelles. The acceleration of decomposition reaction of monochloramines of amino acids in the presence of CTAB micelles is ascribed to the increased reactivity in the micellar pseudophase as compared with that in aqueous phase as inferred from the obtained values of km and kw. From studying the removal efficiency of monochloramines, it was observed that the removal efficiency increases with increasing surfactant concentration, temperature, and the hydrophobicity of side chain of monochloramines of amino acids. 相似文献