一个高粘弹的阴离子蠕虫胶束体系

以频率扫描和稳态剪切实验研究了140 mmol·L^-1羧酸盐gemini 表面活性剂(C₁₄Φ₂C₁₄)在100 mmol·L^-1 NaBr 条件下溶液的流变行为. 在低剪切频率时, 溶液呈现出具有单一松弛时间特性的Maxwell 流体行为.通过活的高分子模型(living polymer model)分析,C₁₄Φ₂C₁₄体系在25℃ 时形成了很长的蠕虫胶束(3.6-6.8μm). 冷冻透射电镜也观察到蠕虫胶束的形成. 这些胶束相互缠绕, 形成了很黏稠的溶液(零剪切粘度高达1.10×10⁴ Pa·s), 外观呈现胶状. 随着温度升高至70℃, 体系的相对粘度仍旧保持很高(1.8×10⁴), 这在阴离子表面活性剂蠕虫胶束溶液中是很少见的. 体系的流动活化能(E_a)约为(141±5) kJ·mol^-1. 利用动态光散射测定了C₁₄Φ₂C₁₄聚集体的尺寸分布, 证实了这个表面活性剂在5-10 mmol·L^-1的低浓度时生成了约100 nm的大聚集体, 这些大聚集体随着表面活性剂浓度的增加很容易转化成棒状直至蠕虫胶束.     

谷氨酸功能胶束温和催化水解甲基-β-D-纤维二糖苷

合成了一种含有谷氨酸残基的长链烷基表面活性剂N^α-十二烷基-L-谷氨酸. 研究了表面活性剂所形成的胶束体系在较温和条件下催化纤维素模型物甲基-β-D-纤维二糖苷(MCB)水解的反应. 研究表明此功能胶束对MCB水解为葡萄糖的反应在较低的温度(90℃)下就表现出明显的催化作用, 在pH 5.0附近具有最佳的催化水解效果.根据胶束催化的相分离模型获得MCB水解的一级反应速率常数(km).研究了胶束与组氨酸(His)或谷氨酸(Glu)所组成的复配体系对MCB的催化水解作用. 结果表明: 氨基酸小分子的加入极大地促进了水解反应的进行, 而胶束与氨基酸在1:1的摩尔浓度配比时催化效果最好. 温度对水解反应速率以及副产物的产生有明显的影响. 在130℃, pH 5.0的水溶液中, 胶束与谷氨酸的复配体系催化MCB水解反应1.5 h后的葡萄糖收率可达到36.6%. 本文也对此催化体系催化MCB水解反应动力学进行了研究, 获得了催化反应的表观一级速率常数(k_obsd), 计算得到催化水解反应生成葡萄糖的活化能(E_a)为97.18 kJ·mol^-1.     

C2H3与CH3F氢抽提反应机理与动力学性质

采用双水平直接动力学方法对C₂H₃与CH₃F氢抽提反应进行了研究. 在QCISD(T)/6-311++G(d, p)//B3LYP/6-311G(d, p)水平上, 计算的三个反应通道R1、R2和R3的能垒(ΔE^≠)分别为43.2、43.9和44.1 kJ·mol^-1, 反应热为-38.2 kJ·mol^-1. 此外, 利用传统过渡态理论(TST)、正则变分过渡态理论(CVT)和包含小曲率隧道效应(SCT)的CVT, 分别计算了200-3000 K温度范围内反应的速率常数k^TST、k^CVT和k^CVT/SCT. 结果表明: (1) 三个氢抽提反应通道的速率常数随温度的增加而增大, 其中变分效应的影响可以忽略, 隧道效应则在低温段影响显著; (2) R1反应是主反应通道, 但随着温度的升高, R2反应的竞争力增大, 而R3反应对总速率常数的影响很小.     

AuCl3催化2-(1-炔基)-2-烯基酮合成多取代呋喃的机理

采用密度泛函理论的B3LYP泛函对AuCl₃催化的2-(1-炔基)-2-烯基酮与亲核试剂反应的机理进行了研究, 得到了反应的最优路径. 结果表明, 整个反应的决速步骤是羟基H转移到AuCl₃的配体Cl上, 其活化能为49.3 kJ·mol^-1. 通过计算发现, 催化剂AuCl₃的配体Cl原子在反应中有重要的作用, 它不仅稳定配合物, 而且直接参与反应, 协助质子的转移, 显著降低质子转移的活化能(由71.5 kJ·mol^-1降低到49.3 kJ·mol^-1). 另外还讨论了HBF₄不能催化此反应的可能原因, 计算结果与实验结果一致.     

含氟表面活性剂溶液的动态表面张力研究

本文研究了阳离子氟表面活性剂CF₃CF₂CF₂O(CF(CF₃)CF₂O)₂CF(CF₃)CONH(CH₂)₃N⁺(C₂H₅)₂CH₃I^-(简写FC-4 )的动态表面性质，利用Krüss K12和MBP动态表面张力仪分别测定了该体系的平衡表面张力和动态表面张力。由平衡表面张力测定结果得到了临界胶束浓度和表面吸附量。利用渐进的Ward and Tordai方程对动态数据进行了分析。结果表明：在吸附的最初阶段符合扩散控制模型，而在吸附的后期，证明了吸附势垒的存在，表明在吸附后期属于混合动力学模型。计算得出25 ℃时，该体系势垒约在25到35 kJ/mol. 由于氟表面活性剂分子间作用力小，表面压是导致吸附势垒的主要原因。     

CH2(COO)2Cu·2H2O热分解的非等温动力学研究

The thermal dehydration and decomposition kinetics of CH₂(COO)₂Cu·2H₂O were investigated using the non-isothermal method by thermogravimetry (TG) technique in N₂. The iterative iso-conversional methods were applied to calculate the activation energy E_a of dehydration and decomposition， and the most probable mechanism function G(α) was determined by means of the master plots method. The pre-exponential factor A was obtained on the basis of E_a and G(α). Kinetic parameters (E_a and lnA) of dehydration were given as: E_a=139.79 kJ·mol^-1， ln(A/s^-1)=47.38. The mechanism function of the dehydration was G(α)=[-ln(1-α)]^2/3， and the decomposition of CH₂(COO)₂Cu proceeds to completion by two distinct reactions. These two reactions overlap in the transition process (0.45<α<0.65). Kinetic parameters (E_a and lnA )of the first reaction of decomposition were: E_a=201.15 kJ·mol^-1， ln(A/s^-1)=52.29， and the mechanism function was G(α)=[1-α]^-0.37. And in the second reaction G(α)=α+(1-α)ln(1-α)， E_a=156.74 kJ·mol^-1， ln(A/s^-1)=39.58.     

CTAB对H2O2氧化抗坏血酸反应动力学的影响

H₂O₂氧化抗坏血酸H₂A的反应为一复杂过程,其过程可用下面可逆连续反应来描述:HA－＋H₂O₂ A,本文用热导式热量计研究了该复杂反应在25 ℃和pH=7的磷酸缓冲溶液(离子强度μ=0.1 mol•L^－1)以及在阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)存在下的反应动力学, 获得了不同CTAB浓度下该复杂反应的表观动力学参数k₁、k₂和k_－1.研究结果表明,表面活性剂CTAB单体分子对反应参数k_－1影响不大, 但却能催化第一步正向反应使k₁变大,而使k₂减小; 在临界胶束浓度cmc附近k₁达到最大值,随后又降低；低浓度胶束对k_-1影响不大,而使k₂增大；高浓度胶束则使k_-1增大而使k₂减小. 低浓度CTAB胶束对的活性影响不大, 而高浓度CTAB胶束将较显著地促进的歧化过程, 减缓的氧化过程. 胶束的静电效应、疏水效应和局部浓聚效应是影响上述反应的重要因素.     

阴离子对阳离子表面活性剂在Al(OH)3、CaCO3粉体上吸附的影响

研究了阳离子表面活性剂十六烷基二甲基烯丙基氯化铵(CDAAC)在Al(OH)₃/水、CaCO₃/水界面上的吸附,探讨了无机阴离子对吸附量及表面电荷的影响,测定了样品的接触角和比表面。结果表明PO^3-₄的加入可提高Al(OH)₃、CaCO₃表面负电荷,有利于吸附,经吸附改性后的样品具有憎水性。     

有机电解质在胶束催化聚苯乙烯氯甲基化反应中的作用

在实施聚苯乙烯氯甲基化反应的胶束催化体系中加入四丁基溴化铵 ((Bu)₄NBr, TBAB), 研究了有机电解质TBAB对胶束催化反应的影响规律. 实验结果表明, 在非离子表面活性剂NP-10及阴离子表面活性剂SDS的胶束催化体系中, TBAB的加入使聚苯乙烯氯甲基化反应的速率明显增大, 前者尤为突出；而在阳离子表面活性剂CTAB的胶束催化体系中, TBAB的加入几乎对反应速率无促进作用. 这种结果一方面归因于加入电解质TBAB会降低SDS的临界胶束浓度, 从而增强对聚苯乙烯四氯化碳溶液的增溶能力；更主要的原因是TBAB的丁基与表面活性剂碳氢链间的疏水相互作用会使季铵离子(Bu)₄N⁺嵌入SDS的胶束之中, 结合到NP-10的胶束表面, 使SDS胶束的阴离子头基对亲核取代反应(控制步骤)的禁阻作用得以减缓, 使NP-10的胶束表面携带了正电荷, 显著促进亲核取代反应的进行, 而对于CTAB的胶束, 由于静电排斥作用, 季铵离子(Bu)₄N⁺不能接近CTAB的胶束, 故TBAB的加入对聚苯乙烯氯甲基化反应不产生作用.     

统计方法校正O3LYP方法计算的生成热

由于引入各种内在近似, 密度泛函理论存在固有误差. 本文采用O3LYP/6-311+G(3df, 2p)//O3LYP/6-31G(d)计算了220个中小型有机分子的生成热(Δ_fH_calc^Θ), 随后应用神经网络(ANN)和多元线性回归(MLR)方法对Δ_fH_calc^Θ进行校正. 采用计算得到的生成热、零点能、分子中原子总数、氢原子个数、双中心成键电子数、双中心反键电子数、单中心价层孤对电子数、单中心内层电子数作为ANN和MLR的描述符. 以180个分子作为训练集构造ANN或MLR模型, 并对40 个独立测试集分子的Δ_fH_calc^Θ进行了预测. 结果表明: 经过ANN和MLR校正后,训练集分子生成热的理论计算值和实验值间的均方根偏差(RMSD)从24.7 kJ·mol^-1分别降低到11.8、13.0 kJ·mol^-1; 独立测试集分子的RMSD从21.3 kJ·mol^-1分别降低到10.4、12.1 kJ·mol^-1. 因此ANN模型的拟合和预测能力要明显优于MLR模型.     

Micellization and synergistic interaction of binary surfactant mixtures based on sodium nonylphenol polyoxyethylene ether sulfate

Mixed micelle formation and synergistic interactions of binary surfactant combinations of sodium nonylphenol polyoxyethylene ether sulfate (NPES) with typical surfactants such as sodium dodecyl sulfate (SDS), Triton X-100 (TX100), cetyl trimethyl ammonium bromide (CTAB), and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) at 25 degrees C in the presence of NaCl have been investigated. The critical micelle concentration of the binary mixtures has been quantitatively estimated by steady-state fluorescence measurements. The micellar characteristics such as composition, activity coefficients, and mutual interaction parameters have been estimated following different theoretical treatments. Investigation on the micellization and synergistic interaction of NPES with four kinds of surfactants showed that the behavior of the binary mixture deviated from the ideal state. The analysis revealed that the interaction parameter values (beta) varied with variation of solvent composition. Besides the strong electrostatic attraction between the oppositely charged surfactant NPES-CTAB mixture, the interaction between NPES and SDS also showed far more deviation from ideal behavior than that of TX100 and AOT. The reason for the synergism is also discussed and the results show that an ionic and a nonionic surfactant character existed concurrently in NPES due to the combination of a sulfate group and polyoxyethylene as a hydrophilic moiety. Zeta potential and diffusion coefficient measurements of micelles confirmed the synergistic interaction between the binary surfactants.     

Unlike surfactant–polymer interactions of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate with water-soluble polymers

Single and mixed micelle formation by sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) and their mixtures in pure water and in the presence of water-soluble polymers such as Synperonic 85 (triblock polymer, TBP), hydroxypropylcellulose (HPC), and carboxymethylcellulose sodium salt (CMC) were studied with the help of conductivity, pyrene fluorescence, cyclic voltammetry, and viscosity measurements. Conductivity measurements showed a single aggregation process for pure surfactants and their mixtures both in pure water as well as in the presence of water-soluble polymers. Triple breaks corresponding to two aggregation processes for SDS, SDBS, and their mixture in the presence of TBP were observed from fluorescence measurements. The first one demonstrated the critical aggregation process due to the adsorption of surfactant monomers on TBP macromolecule. The second one was attributed to the participation of surfactant–polymer aggregates formed at the first one, in the micelle formation process. The aggregation number ( N _agg) of single and mixed micelles and diffusion coefficient ( D) of electroactive probe were computed from the fluorescence and cyclic voltammetry measurements, respectively. Both parameters, along with the viscosity results, indicated stronger SDS–polymer interactions in comparison to SDBS–polymer interactions. Mixed surfactant–polymer interactions showed compensating effects of both pure surfactants. The nature of mixed micelles was found to be ideal in all cases, as evaluated by applying the regular solution and Motomura's approximations.     

Interaction of Nonionic Surfactant Triton-X-100 with Ionic Surfactants

The interaction in two mixtures of a nonionic surfactant Triton-X-100 (TX-100) and different ionic surfactants was investigated. The two mixtures were TX-100/sodium dodecyl sulfate (SDS) and TX-100/cetyltrimethylammonium bromide (CTAB) at molar fraction of TX-100, α_TX-100 = 0.6. The surface properties of the surfactants, critical micelle concentration (CMC), effectiveness of surface tension reduction (γ_CMC), maximum surface excess concentration (Γ_max), and minimum area per molecule at the air/solution interface (A _min) were determined for both individual surfactants and their mixtures. The significant deviations from ideal behavior (attractive interactions) of the nonionic/ionic surfactant mixtures were also determined. Mixtures of both TX-100/SDS and TX-100/CTAB exhibited synergism in surface tension reduction efficiency and mixed micelle formation, but neither exhibited synergism in surface tension reduction effectiveness.     

Kinetics of micellization: its significance to technological processes

The association of many classes of surface active molecules into micellar aggregates is a well-known phenomenon. Micelles are often drawn as static structures of spherical aggregates of oriented molecules. However, micelles are in dynamic equilibrium with surfactant monomers in the bulk solution constantly being exchanged with the surfactant molecules in the micelles. Additionally, the micelles themselves are continuously disintegrating and reforming. The first process is a fast relaxation process typically referred to as τ₁. The latter is a slow relaxation process with relaxation time τ₂. Thus, τ₂ represents the entire process of the formation or disintegration of a micelle. The slow relaxation time is directly correlated with the average lifetime of a micelle, and hence the molecular packing in the micelle, which in turn relates to the stability of a micelle. It was shown earlier by Shah and coworkers that the stability of sodium dodecyl sulfate (SDS) micelles plays an important role in various technological processes involving an increase in interfacial area, such as foaming, wetting, emulsification, solubilization and detergency. The slow relaxation time of SDS micelles, as measured by pressure-jump and temperature-jump techniques was in the range of 10⁻⁴–10¹ s depending on the surfactant concentration. A maximum relaxation time and thus a maximum micellar stability was found at 200 mM SDS, corresponding to the least foaming, largest bubble size, longest wetting time of textile, largest emulsion droplet size and the most rapid solubilization of oil. These results are explained in terms of the flux of surfactant monomers from the bulk to the interface, which determines the dynamic surface tension. The more stable micelles lead to less monomer flux and hence to a higher dynamic surface tension. As the SDS concentration increases, the micelles become more rigid and stable as a result of the decrease in intermicellar distance. The smaller the intermicellar distance, the larger the Coulombic repulsive forces between the micelles leading to enhanced stability of micelles (presumably by increased counterion binding to the micelles). The Center for Surface Science & Engineering at the University of Florida has developed methods using stopped-flow and pressure-jump with optical detection to determine the slow relaxation time of micelles of nonionic surfactants. The results show relaxation times τ₂ in the range of seconds for Triton X-100 to minutes for polyoxyethylene alkyl ethers. The slow relaxation times are much longer for nonionic surfactants than for ionic surfactants, because of the absence of ionic repulsion between the head groups. The observed relaxation time τ₂ was related to dynamic surface tension and foaming experiments. A slow break-up of micelles, (i.e. a long relaxation time τ₂) corresponds to a high dynamic surface tension and low foamability, whereas a fast break-up of micelles, leads to a lower dynamic surface tension and higher foamability. In conclusion, micellar stability and thus the micellar break-up time is a key factor in controlling technological processes involving a rapid increase in interfacial area, such as foaming, wetting, emulsification and oil solubilization. First, the available monomers adsorb onto the freshly created interface. Then, additional monomers must be provided by the break-up of micelles. Especially when the free monomer concentration is low, as indicated by a low CMC, the micellar break-up time is a rate limiting step in the supply of monomers, which is the case for many nonionic surfactant solutions. Therefore, relaxation time data of surfactant solutions enables us to predict the performance of a given surfactant solution. Moreover, the results suggest that one can design appropriate micelles with specific stability or τ₂ by controlling the surfactant structure, concentration and physico-chemical conditions, as well as by mixing anionic/cationic or ionic/nonionic surfactants for a desired technological application.     

Removal of cadmium ions using micellar-enhanced ultrafiltration with mixed anionic-nonionic surfactants

Micellar-enhanced ultrafiltration (MEUF) was used to remove cadmium ions from wastewater efficiently. In this study the nonionic surfactants polyoxyethyleneglycol dodecyl ether (Brij35) and polyoxyethylene octyl phenyl ether (TritonX-100) were for micellar-enhanced ultrafiltration to lower the dosage of the anionic surfactant sodium dodecyl sulfate (SDS). The surfactant critical micelle concentration (CMC) and the degree of micelle counterion binding were investigated. The effects of nonionic surfactant addition on the efficiency of cadmium removal, the residual quantities of surfactant, the permeate flux and the secondary membrane resistance were investigated. A comparison between MEUF with SDS and MEUF with mixed anionic–nonionic surfactants was undertaken. The results show that the addition of Brij35 or TritonX-100 reduced the CMC of SDS and the degree of counterion binding for the micelles. Due to these variations the Cd²⁺ rejection efficiency was at a maximum when the Brij35:SDS and the TritonX-100:SDS molar ratio was 0.5. The Cd²⁺ rejection efficiency in MEUF with SDS is higher than for MEUF with mixed surfactants when the total dose of surfactant is constant. The permeate flux of MEUF with SDS is higher than that for MEUF with mixed surfactants while the secondary resistance of MEUF with SDS is less than that of MEUF with mixed surfactants.     

Diffusion in surfactant solutions

The diffusion coefficients in water of Triton X-100 and sodium dodecyl sulfate were measured as a function of concentration using the Taylor dispersion technique. For Triton X-100, a nonionic surfactant, the diffusion coefficient drops from 7.4 × 10^-7 cm²/sec at 0.45 g/liter to 6.45 x 10^-7 cm²/sec at 5 g/liter. The diffusion coefficient of methyl yellow solubilized in Triton X-100 is close to that of the surfactant. This behavior is quantitatively consistent with a chemical equilibrium between monomer and micelle. For sodium dodecyl sulfate, an anionic surfactant, the diffusion coefficient increases from 1.76 x 10^-6 cm²/sec at 0.01 M to 4.53 x 10^-6 cm²/sec at 0.125 M. The increase is less when 0.1 M NaCl is added. The diffusion coefficient of the methyl yellow solubilized by the SDS is significantly less than that of the surfactant, particularly at low ionic strength. This behavior can be quantitatively explained by including electrostatic coupling between monomer, micelle, and counterion.     

Effect of anionic and cationic micelles on the oxidation of <Emphasis Type="SmallCaps">D</Emphasis>-glucose by cerium(IV) in presence of H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

The influence of surfactants (anionic and cationic) on the reactivity of the redox couple cerium(IV) and D-glucose was examined spectrophotometerically. Various kinetic parameters have been determined in the absence and presence of surfactants. The kinetics were followed by monitoring the disappearance of the absorbance of cerium(IV) at 385 nm. The reaction obeyed first-order kinetics with respect to [D-glucose] in both media. No effect of anionic micelles of sodium dodecyl sulfate (SDS) was observed due to electrostatic repulsion between the negative head group of SDS and reactive species of cerium(IV) (Ce(SO₄) ₃ ²⁻ ). A twofold increase in the oxidation rate was observed in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB). The observed catalytic role has been analyzed in terms of the Menger–Portnoy model. The effects of various inorganic salts (Na₂SO₄, NaNO₃ and NaCl) were also studied in micellar media.     

Spectrophotometric study of interaction and solubilization of procaine hydrochloride in micellar systems

The interaction of Procaine hydrochloride (PC) with cationic, anionic and non-ionic surfactants; cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and triton X-100, were investigated. The effect of ionic and non-ionic micelles on solubilization of Procaine in aqueous micellar solution of SDS, CTAB and triton X-100 were studied at pH 6.8 and 29°C using absorption spectrophotometry. By using pseudo-phase model, the partition coefficient between the bulk water and micelles, K_x, was calculated. The results showed that the micelles of CTAB enhanced the solubility of Procaine higher than SDS micelles (K_x = 96 and 166 for SDS and CTAB micelles, respectively) but triton X-100 did not enhanced the solubility of drug because of weak interaction with Procaine. From the resulting binding constant for Procaine-ionic surfactants interactions (K_b = 175 and 128 for SDS and CTAB surfactants, respectively), it was concluded that both electrostatic and hydrophobic interactions affect the interaction of surfactants with cationic procaine. Electrostatic interactions have a great role in the binding and consequently distribution of Procaine in micelle/water phases. These interactions for anionic surfactant (SDS) are higher than for cationic surfactant (CTAB). Gibbs free energy of binding and distribution of procaine between the bulk water and studied surfactant micelles were calculated.      

Quasielastic light-scattering studies of micellar sodium dodecyl sulfate solutions at the low concentration limit

Correlation functions of scattered light intensity of carefully purified sodium dodecyl sulfate (SDS) solutions were measured as a function of tenside concentration and NaCl concentration of the aqueous phase. The correlation functions were analyzed by taking into account the influence of the Coulomb interaction between the micelle (macroion) and small electrolyte ions on the diffusion coefficient. Values of the hydrodynamic radius, the aggregation number, and the effective surface charges were obtained. The aggregation number increases from N = 27 to N = 95 upon increasing the NaCl concentration from 0 to 0.05 mole per liter, while it remains constant when the salt concentration increases further up to 0.2 mole per liter. The effective charge of the micelles decreases with increasing NaCl content in the whole concentration region studied. These results could be interpreted qualitatively in terms of a model which relates the existence of an equilibrium size of the micelles to the balance between hydrophobic and Coulomb interactions. Our results lead to the conclusion that at least up to an NaCl concentration of 0.2 mole per liter the SDS-micelles exhibit an oblate spherical shape rather than a cylindrical form.     

Effects of nonionic surfactant and sodium dodecyl sulfate layers on electroacoustics of hexadecane/water emulsions

Hexadecane-in-water emulsion droplets were formed in a homogeniser in the presence of a mixture of an anionic surfactant (sodium dodecyl sulfate, SDS) and nonionic surfactants of various chain lengths [nonylphenol ethoxylate (C₉φE_N, N=100, 40 and 30) or an alcohol ethoxylate (Brij35)]. The dynamic mobility of the oil droplets was then measured using a flow-through version of an AcoustoSizer. Large changes were observed in the dynamic mobility of the particles formed with the mixed surfactants compared to particles formed with SDS alone. O'Brien's “gel layer” model was employed to interpret the data. The characteristics of the adsorbed layer appeared to be similar whether the nonionic surfactant was adsorbed concurrently with the SDS as the emulsion formed or was merely added afterwards to the emulsion established. The particle size, the charge and the molar fraction of SDS had virtually no effect. The layers formed with the nonionic surfactants decreased in thickness with decreasing molecular weight as expected. Passage through the homogeniser itself had no effect on the properties of the largest nonionic surfactant and, hence, on the adsorption layer formed with it. Received: 4 October 2000 Accepted: 16 October 2000