盐对C8-卵磷脂胶团溶液相分离的作用

借助描述胶团溶液相变过程的唯象理论，结合有关电解质作用的理论模型，分析了盐对Ｃ８－卵磷脂胶团相分离的作用，导出加盐后Ｃ８－卵磷脂胶团溶液的吉布斯自由能，并据此推导出该溶液相谱临界温度随盐度类型和离子强度变化的规律，以及溶液中盐离子与卵磷肥分子相互作用的机制。     

用弱电解质理论研究水溶液中SDS胶团的电离行为

在临界胶团浓度以上,十二烷基硫酸钠(SDS)在溶液中形成聚集态的胶团,从而表现出不同于一般强电解质的电导行为.针对这一特点提出了一种胶团电离模型,即将胶团作为一种弱电解质,用弱电解质电导理论来描述其溶液电导的变化规律,导出SDS胶团电离度的计算式,并得到该溶液电导实测数据的验证.     

表面活性剂在固液界面上的吸附理论

本文根据二阶段吸附模型和质量作用定律,首次导出表面活性剂在固液界面上吸附等温线通用公式,可定量解释实验测得的各种吸附等温线,并可求得表面胶团(或反胶团)的聚集数和二吸附阶段的平衡常数。吸附热力学计算表明,表面胶团亦为疏水作用的熵驱动过程,反胶团化则为极性基间相互作用或形成氢键的结果。     

溴代十四烷基吡啶胶团长大的光子相关谱研究

本文用光子相关谱方法在15—85 ℃温度范围内, 研究了溴代十四烷基吡啶(TPB)胶团在高盐量介质(0.5—2.0M NaBr)中的长大规律。自光子相关实验测定了胶团的平均流体力学半径。增加盐量、降低温度和增大活性剂浓度均使胶团变大。TPB胶团长大时由球转变为棒。自实验测量结果求算了在0.5 M和1.0 M盐中支配球-棒转变的平衡常数及热力学函数值。本文检验了梯子模型对TPB体系的适用性, 并对2 M盐介质中TPB胶团的长大具有不同的特征作了讨论。     

正负离子表面活性剂反胶团与反相微乳研究

研究了以癸烷为油相的十一烯酸癸胺正负离子表面活性剂体系对水的加溶作用。结果表明此体系在一定组成范围内可以形成均匀透明的反胶团或反相微乳液。升高温度和添加酸、碱、盐可以使形成反胶团或反相微乳的组成范围扩大。在正负离子表面活性剂中加入离子型表面活性剂、特别是负离子型表面活性剂,也有类似的作用。     

阳离子表面活性剂混合胶团对2,4-二硝基氯苯水解反应的 催化作用

研究了阳离子表面活性剂混合胶团对2,4-二硝基氯苯(DNCB)碱性水解反应的催化作用。结果表明：(1)在十六烷基三甲基溴化铵(CTAB)和十六烷基溴化吡啶(CPB)混合溶液中DNCB水解一级速率常数k1与混合胶团中CTAB或CPB的摩尔分数有直线关系,表面活性剂形成理想的混合胶团。(2)辛基三甲基省化铵(OTAB)与CTAB,CPB的cmc值相差很大,在它们的混合胶团中OTAB含量极少,DNCB水解k1与CPB/OTAB混合胶团中CPB摩尔分数的关系与直线呈负偏差。(3)在CTAB(或CPB)与OTAB混合体系中OTAB起溴盐作用,使催化活性降低。用假相离子交换(PIE)模型对所得结果给出了定量的处理和解释。     

全氟辛酸与十二烷基硫酸钠混合溶液中的胶团形成

用表面张力法、电导法,pH测定法研究全氟辛酸-十二烷基硫酸钠混合水溶液的胶团形成及全氟辛酸胶团的特性.结果表明:(1)电导法与pH测定法弥补了表面张力法的不足,进一步证明在碳氟链表面活性剂与碳氢链表面活性剂混合水溶液中形成两种胶团.(2)全氟辛酸与十二烷基硫酸钠混合水溶液中所形成的两种胶团,分别基本上由全氟辛酸和十二烷基硫酸钠组成.十二烷基硫酸钠的存在对全氟辛酸胶团的形成不显示影响.全氟辛酸的氢离子对十二烷基硫酸钠胶团显示反离子效应.(3)全氟辛酸是典型的离子型表面活性剂,由于它对氢离子的结合力特别强,其胶团几乎是电中性的.这一特性可以解释全氟辛酸-十二皖基硫酸钠混合溶液胶团形成的机制.     

C_(16)mimBr/Tween20混合胶团的聚集行为和热力学性质研究

通过测定表面张力,研究了离子液体型表面活性剂溴化1-十六烷基-3-甲基咪唑(C16mim Br)和非离子表面活性剂Tween20混合体系在水溶液中的聚集行为和热力学性质。利用Rubingh和Maeda模型计算了混合物中各组分在胶团相中的组成、相互作用参数以及胶团形成的热力学性质。结果表明,两组分在胶团形成过程中存在协同效应。非离子组分在胶团相中的组成高于本体溶液中的组成。分析和探讨了胶团形成的驱动力和稳定性。     

乙二醇对烷基三甲基溴化铵胶团化行为的影响

利用电导法研究了烷基三甲基溴化铵表面活性剂(CnTAB,n=12,14,16),即十二烷基三甲基溴化铵(DTAB),十四烷基三甲基溴化铵(TTAB)和十六烷基三甲基溴化铵(CTAB),在混合极性溶剂乙二醇/水(体积分数0～40%)中的胶团化行为。考察了温度对胶团形成的影响,应用相分离模型估算了三个表面活性剂的胶团热力学参数。结果表明临界胶团浓度(cmc)和反离子解离度(α)都随乙二醇组分的增加而增大。在乙二醇/水混合溶剂中胶团形成的标准吉布斯自由能相差很小,混合焓都是负值,而混合熵都为正值,说明焓-熵补偿效应在胶团形成中起主导作用。     

吸附胶团和吸附胶团催化

介绍了吸附胶团的结构特点、影响吸附胶团催化的一些因素和在固体表面上的固定化表面活性剂体系的催化作用。吸附胶团是表面活性剂在固-液界面形成的缔合结构,它可以是吸附单层、双层、半球形、球形等。吸附胶团和利用接枝等技术在固体表面形成的不溶性表面活性剂体系,在一定条件下,可对某些反应起催化作用,有利于提高反应产率并使反应产物分离变得容易,这将使胶团催化的实际应用成为可能。     

表面活性剂胶束化物理化学性质研究

通过电导法考查温度和盐浓度对十二烷基硫酸钠(SDS)临界胶束浓度(CMC)的影响,研究表面活性剂形成胶束过程的物理化学性质。根据拟相分离模型求得胶束化热力学函数,并讨论体系电导活化能随温度和SDS浓度变化关系。结果表明:SDS的CMC随温度升高而增加,随氯化钠浓度增大而减小。在热力学上SDS在水溶液中形成胶束是一个自发、放热、熵增的过程;在动力学上,SDS溶液电导率与温度关系符合Arrhenius公式,通过电导活化能信息可揭示离子型表面活性剂形成胶束的机理特征。     

聚氧乙烯-聚氧丙烯嵌段共聚物在水溶液中的胶束化作用

本实验采用表面张力法,苯红紫可见光吸收法测定L64,AE32,AP221等三种不同结构的聚氧乙烯-聚氧丙烯嵌段共聚物的临界胶束形成浓度CMC,发现L64与AE32在低浓度下形成单分子胶束,在高浓度下形成聚集胶束。AP221则只在较低的浓度下形成聚集胶束。不同温度下CMC的测定结果表明温度对L64形成单分子胶束的CMC影响较小,而聚集胶束的浓度则随着温度升高而迅速下降,后者胶束形成热ΔH较高,为140.6kJ/mol。     

Mixed micelles formed by SDS and a bolaamphiphile with carbohydrate headgroups

The formation of micelles in aqueous mixtures of a carbohydrate-based bolaamphiphile and sodium dodecyl sulfate (SDS) is investigated by surface tension and small-angle neutron scattering. The obtained values of critical micelle concentration (CMC) are analyzed within the framework of regular solution theory. Synergetic interactions between the bolaamphiphile and SDS are observed (parameter beta is negative; a minimum in the plot CMC vs composition). SANS data are collected for mixtures containing protonated and deuterated SDS. This gives us the possibility to conclude that mixed micelles with a homogeneous distribution of surfactant molecules within the micelle are formed. The shape of the micelles is found to be slightly oblate.     

羧甲基纤维素-十二烷基醇聚氧乙烯醚丙烯酸酯共聚物表面活性剂在水溶液中的胶束形态

采用动态激光光散射及环境扫描电镜研究了羧甲基纤维素型高分子表面活性剂在水溶液中的胶束形态 .结果表明 ,共聚物在水溶液中的形态完全不同于羧甲基纤维素分子 ,亲水疏水链段的引入 ,使共聚物分子聚集形成了以疏水链段为核心的棍状胶束结构 .高分子表面活性剂水溶液体系的归一化一级相关函数不符合单指数衰减 ,表明胶束形态的多分散性 .在 0 .0 0 5%～ 1 %浓度范围内 ,胶束粒子大小均分布在两个区域 ,随共聚物浓度增大 ,低粒径区保持在 3 0～ 1 0 0nm范围 ,为单分子区 ;而高粒径区随浓度增大移向更高值 ,表明多分子胶束不断长大 .     

Micellisation thermodynamics of sodium lauroylsarcosinate in water–alcohol binary mixtures

Aggregation of sodium lauroylsarcosinate (SLS) in aqueous solutions of methanol, ethanol, propanol and ethylene glycol at 288–313 K has been determined from conductivity measurement in the range 0–20% v/v of additives. The precise values of the critical micelle concentration (CMC) and the degree of counter-ion dissociation of micelles were obtained at each temperature by fitting the specific conductivity-surfactant concentration curve to the integrated form of the Boltzmann-sigmoid equation. The CMC was found to increase with increase in additive concentrations in the case of methanol and ethylene glycol, while it decreases with increase in ethanol and propanol concentration. The equilibrium model of micelle formation was applied to obtain the thermodynamic parameters of micellisation. The Gibbs free energies were observed to vary only slightly with temperature and additive concentrations. Enthalpy–entropy compensation was observed for all the systems with a constant compensation temperature of ≈300 K and negative compensation enthalpy.     

FLUORESCENCE PROBE STUDIES ON THE SECOND CRITICAL MICELLE CONCENTRATION OF SEVERAL KINDS OF SURFACTANTS

The fluorescence intenstiy ratios (F₂/F₁) of excimer (F₂) to monomer (F₁) of probe (pyrene) were measured as a function of the concentration of the surfactant in several systems, which consist of sodium hexadecyl sulfonate (C₁₆As)-anionic surfactant, cetyltrimethylammonium bromide (CTAB)-cationic surfactant and pentaoxyethylene decyl ether (C₁₀E₅)-nonionic surfactant. The second CMC values were obtained according to F₂/F₁ ~ surfactant concentration curve break. In addition, we also studied the variation of second CMC vs NaCl concentration. It was found that the second CMC values of C₁₆A₅ and CTAB decreased with the increase of NaCl concentration. But the present of NaCl had no influence on the second CMC value of C₁₀E₅. Results showed that sphere-shaped micelles turn into rod-like micelle at the second CMC. The results were interpreted in terms of diffusion of pyrene molecules and the distribution of pyrene among micelles.     

Micellization of bile salts in aqueous medium: a fluorescence study

Owing to the physiological importance of the micellization process of bile salts, the critical micelle concentration (CMC) becomes a fundamental parameter in the evaluation of their biological activities. The present study suggests fluorescence probing, using 1,6-diphenylhexatriene (DPH), as a simple, convenient, sensitive and economic method for monitoring the micellization process of bile salts in aqueous medium. Three independent parameters: fluorescence intensity, anisotropy and lifetime of DPH have been employed successfully for determining the CMC of two bile salts, sodium deoxycholate (NaDC) and sodium cholate (NaC), in aqueous medium. The CMC values reported by all the above three parameters of DPH are found to be same and it is 16 mM for NaC and 6 mM for NaDC at 25 degrees C in unbuffered solution. The effect of temperature and ionic strength on the micellization process has also been investigated employing DPH as a fluorescent probe. Increasing temperature leads to the formation of fluffier micelles with less rigid interior for both NaC and NaDC. The micelle core of NaC is less perturbed by the presence of NaCl whereas in case of NaDC, the aggregates provide DPH a more nonpolar and rigid environment in presence of NaCl than that in absence of salt.     

Concentrations of Monomers and Cylindrical Micelles above the Second CMC

Based on thermodynamically substantiated linear dependence of the work of cylindrical micelle formation on the aggregation number within a wide range of aggregation numbers where the cylindrical micelles are accumulated in a surfactant solution, the second critical micellization concentration (CMC) is introduced as an overall surfactant concentration at which the ratio of the total amount of substance in cylindrical micelles to the amount of substance in monomers is equal to 0.1, i.e., it is already noticeable. It is shown that this ratio increases rather rapidly with a monomer concentration. The coefficient of the linear dependence of the work of cylindrical micelle formation on the aggregation number in the important practical situation where the ratios of the total concentration of cylindrical micelles and total amount of substance in these micelles to the monomer concentration are equal by the order of magnitude to 1 and 10⁵, respectively, while disc micelles and extended bilayers are still not appeared. In the same situation, the ratios of the total concentration of spherical micelles and total amount of substance in these micelles to the monomer concentration are equal by the order of magnitude to 1 and 10², respectively. The relationship between the overall surfactant concentration and monomer concentration is found. It is shown that the second CMC exceeds by two orders of magnitude the first CMC corresponding to the onset of the noticeable accumulation of surfactant in spherical micelles. The distribution of cylindrical micelles over the aggregation numbers is analyzed. It is demonstrated that, in agreement with the experiment, the distribution is almost uniform in the considerable part of the wide range of aggregation numbers and drops exponentially in the remaining (right-hand) part of this range. Experimental result is confirmed that the total concentration of cylindrical micelles, the mean value, and the mean statistical scatter of aggregation numbers in a cylindrical micelle is proportional to the square root of the overall surfactant concentration. The balance equation of surfactant amount in the vicinity of the final equilibrium state of a materially isolated solution is linearized. This linearization makes it possible to express the deviations of monomer and aggregate concentrations from their equilibrium values at the lower boundary of the region of the linear dependence of the work of cylindrical micelle formation on the aggregation numbers via the deviations of experimentally observed total concentrations of spherical and cylindrical micelles from their equilibrium values. The case of the solutions of such surfactants, for which spherical shape appeared to be unrealizable due to their molecular structure and packing conditions, is considered separately.     

Cholesterol Monohydrate Dissolution in Bile Salt‐Lecithin Solutions

A modified dissolution rate equation was used to quantitatively investigate the contribution of simple bile salt (BS) micelles and mixed BS‐lecithin (L) micelles to a cholesterol monohydrate (ChM) dissolution. Using a least‐squares technique to assess the relationship between the ChM dissolution rate and BS concentration at a constant L concentration, good curve‐fittings were obtained when the BS monomer concentration was set to equal the critical micellar concentration (CMC). For taurochenodeoxycholate (TCDC), a dihydroxy BS, the resulting values of parameters show that the simple TCDC micelle rate constant (ks) increases, but the mixed TCDC‐L micelle rate constant (kM ) decreases with increasing L concentrations. As for taurocholate (TC), a tri‐hydroxy BS, a ChM dissolution study was conducted over the initial 2 hour period in different TC‐L solutions. A similar curve‐fitting analysis revealed that the simple TC micelle ks is independent of L concentration and is much higher than the kM of mixed TC‐L micelles. Moreover, the outcome of the analysis supports previously reported equilibrium dialysis study results concerning the BS to L ratio of mixed BS‐L micelles. According to the collision theory, the resulting ks and kM values are interpreted.     

Second CMC in surfactant micellar systems

Experimental reports of surfactant systems displaying a second critical micelle concentration (second CMC) have been surveyed. It turns out that surfactant micelles usually show a growth behavior with some typical features. (i) Micelles grow weakly at low surfactant concentrations but may switch to a much stronger growth behavior at higher concentrations. The second CMC is defined as the point of transition from weakly to strongly growing micelles. (ii) Micelles are found to be non-spherically shaped below the second CMC. (iii) At the second CMC micelles are found to be much smaller, with aggregation numbers typically 100–200, than expected for flexible micelles. (iv) Micelles of intermediate size are present in a narrow concentration regime close to the second CMC. (v) Micelles grow much stronger above the second CMC than expected from a sphere-to-rod transition. The conventional spherocylindrical micelle model predicts a smooth growth behavior that contradicts the appearance of a second CMC. Modifying the model by means of including swollen end caps neither account for the presence of micelles with intermediate size, nor the strong growth behavior above the second CMC. Taking into account micelle flexibility is not consistent with the rather low micelle aggregation numbers observed at the second CMC. On the other hand, a recently proposed alternative theoretical approach, the general micelle model, have been demonstrated to take into account basically all features that are typical of experimentally observed micellar growth behaviors.