自由能微扰法研究系列烷基芳基磺酸盐的胶束化焓-熵补偿现象

为了研究不同结构的表面活性剂分子在水溶液中的胶束化焓-熵补偿现象, 采用自由能微扰(FEP)法计算了系列烷基芳基磺酸盐的溶剂化自由能, 并根据胶团化过程的质量作用模型讨论了相关热力学性质. 结果表明: 自由能微扰法得到的溶剂化自由能大小与用传统热力学表面张力法测定的吉布斯自由能相近, 能够用于比较不同结构的烷基芳基磺酸盐间胶束化能力; 烷基芳基磺酸盐在水溶液中的胶束化过程是自发进行的, 且存在焓-熵补偿现象, 补偿温度范围均在(302±2) K; 随着分子结构中芳环向长烷基链中间位置移动, 胶束化能力和胶束的稳定性均下降; 而随着芳环上短烷基链或长烷基链碳数的增加, 形成胶束的能力与稳定性均提高.     

烷基芳基磺酸盐的分子动力学模拟与自由能微扰计算

为研究不同结构的表面活性剂分子在溶液中胶束化能力的差异, 采用分子动力学方法模拟三种烷基芳基磺酸盐在真空和水溶液环境下的结构与相互作用. 利用自由能微扰(FEP)方法计算了水合自由能, 发现与用传统热力学表面张力法测定自制的烷基芳基磺酸盐结果一致. 研究表明: 烷基芳基磺酸盐在水溶液中的胶束化过程是自发进行的, 随着分子结构中芳环向长烷基链中间位置移动, 胶束化能力和胶束稳定性均下降; 疏水基周围水分子的“冰山结构”会影响胶束的稳定性, 而水分子中氢键的生存周期是反映冰山结构变化的重要指标; 同时, 亲水基与水分子间形成氢键的数目会增强或减弱分子脱离胶束体的趋势, 从而影响胶束结构的稳定性.     

十四烷基芳基磺酸盐形成的分子有序组合体

以表面张力法、碘光谱法、水增溶法和相态图法研究了自制的三种十四烷基芳基磺酸盐在不同条件下形成的分子有序组合体(胶束、反胶束和微乳液),并考察了分子结构、溶剂、无机盐和短链醇等对其的影响.结果表明:增加十四烷基芳基磺酸盐分子亲油基支化度,不利于其在水溶液或混合极性溶剂(乙二醇-水)中形成胶束而有利于其在非极性溶剂正庚烷中形成反胶束;溶剂极性的降低,促使表面活性剂溶液由胶束溶液→单体溶液→反胶束溶液转变;无机盐或短链醇的加入促进了水溶液中胶束的形成,且反离子价态数或醇烷基碳原子数越大,越有利于胶束形成;无机盐浓度的增加导致表面活性剂/正丁醇/正辛烷/NaCl/水形成的微乳液体系在一定温度下发生由WinsorI→WinsorIII→WinsorII型的转变.     

不同链长烷基芳基磺酸盐形成微乳液的性质

以Winsor相态图法和拟三元相图法研究了自制的3种不同链长烷基芳基磺酸盐在多组分体系中形成的微乳液的性质, 并考察了分子结构、无机盐和短链醇等的影响. 结果表明, 无机盐浓度的增加导致表面活性剂/正丁醇/正辛烷/NaCl/水形成的微乳液体系在一定温度下发生由WinsorⅠ→ WinsorⅢ→ WinsorⅡ型转变; 随着烷基芳基磺酸盐分子的长烷基链碳原子数的增加, 耐盐能力减弱, 增溶能力提高; 随着醇碳链的增大, 微乳区面积先增大后减小. 当烷基芳基磺酸盐分子结构固定时, 最大微乳液区域醇的选择依据符合Bansal理论. 醇的链长一定时, 随着烷基芳基磺酸盐分子的长烷基链碳原子数的增加, 微乳液的区域变小.     

烷基芳基磺酸盐结构对微乳液相行为的影响

用Winsor相图法研究了自制的6种不同结构的烷基芳基磺酸盐/不同醇/正癸烷/NaCl/水体系在不同温度下所形成的微乳液。 探讨了烷基芳基磺酸盐结构对微乳液相行为的影响。 同时考察了温度和醇对微乳液相行为的影响。 结果表明,随着烷基芳基磺酸盐长烷基链的增长,中相形成盐度S1、中相消失盐度S2、中相盐宽ΔS和最佳盐浓度S*值均减小,最佳中相体积V*M和最佳增容量σ*值均增大;随着烷基芳基磺酸盐分子的芳环向长烷基链中间位置移动,S1、S2、ΔS、S*值均减小,V*M和σ*值均增大;随着温度升高,V*M和σ*值均减小,S1、S2、ΔS、S*值均增大,在25 ℃时,体系无中相微乳液形成;随着正构醇碳原子数的增加,V*M和σ*值均增大,S1、S2、ΔS、S*值均减小。     

二甲基硅氧烷甘醇乙酸基共聚物水溶液的表面活性

通过表面张力的测定, 考察了不同无机盐和温度对二甲基硅氧烷甘醇乙酸基共聚物(PSEP)表面活性的影响, 进而研究PSEP在不同介质中胶束形成热力学性质. 研究表明, NaCl、NaBr和CaCl2的存在可提高PSEP的表面活性. 而且, PSEP的胶束化焓变对熵变呈线性相关, 说明存在焓/熵补偿现象.     

含酯基Gemini表面活性剂在有机醇-水体系中的胶束热力学及聚集行为

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。     

C12-s-C12·2Br与低碳醇混合水溶液胶团化行为的温度效应和焓/熵补偿

季铵盐Gemini表面活性剂C12-s-C12·2Br(s=2,3,4,6)与丙醇、丁醇、戊醇、己醇混合水溶液的In(cmc)随温度升高而逐渐增大.计算所得热力学数据表明,C12-s-C12·2Br与醇混合胶团化过程服从熵驱动机理,也出现了焓/熵补偿现象.随着温度上升,熵驱动力增大,在指定温度时,醇分子烷烃链上碳原子数n增大使△Gm0值减小,胶团结构更加稳定;而增加s使值增大,胶团稳定性下降.     

N-酰基-L-丝氨酸钠表面活性剂的合成和胶束化热力学性质

以L-丝氨酸和长链酰氯为原料,合成了3种不同碳链长度（n=8,12,14）的N-酰基-L-丝氨酸。 并以1H NMR、ESI-MS和元素分析对3种目标产物进行了表征。 采用表面张力法研究了N-酰基-L-丝氨酸钠在298、308、318和328 K时水溶液中的聚集行为,确定了临界胶束浓度（cmc）、临界胶束浓度下的最低表面张力（γcmc）、表面饱和吸附量Γmax。 由cmc和温度的关系,应用相分离模型计算了胶束化热力学参数ΔGom、ΔHom和ΔSom。 结果表明,ΔGom＜0,ΔHom的绝对值比-TΔSom绝对值小的多,说明胶束化过程为熵驱动过程,随着温度的升高,胶束化过程是熵-焓补偿的过程。     

DMF/水溶液中TDBAC与咪唑型离子液体混合胶束的聚集行为及热力学性质

利用电导法研究了298.15 K时十四烷基二甲基苄基氯化铵(TDBAC)与咪唑型离子液体表面活性剂Cn mim Br(n=12,16)混合胶束性质,考察了极性溶剂N,N-二甲基甲酰胺(DMF)对TDBAC/C16mim Br混合体系胶束化的影响。结果表明,混合体系在水溶液和DMF水溶液中都存在协同效应。随DMF体积分数的增加,TDBAC/C16mim Br混合体系临界胶束浓度(cmc)增大,而反离子结合度减小。利用胶束理论模型计算了混合胶束的组成、相互作用参数和活度系数,以及胶束形成混合自由能、混合熵和超额自由能等热力学函数。随DMF体积分数增加,协同作用下降,胶束形成的自发性降低。水溶液中混合胶束形成是焓效应与熵效应共同作用的结果,而在20%DMF水溶液中,胶束形成是熵驱动。     

Aggregation of sodium 1-(n-alkyl)naphthalene-4-sulfonates in aqueous solution: micellization and microenvironment characteristics

In aqueous solution, the micellization and microenvironment characteristics of the micelle assemblies of three anionic surfactants, sodium 1-(n-alkyl)naphthalene-4-sulfonates (SANS), have been investigated by steady-state fluorescence and time-resolved fluorescence decay techniques using pyrene, Ru(bpy)3(2+), and 1,6-diphenyl-1,3,5-hexatriene as fluorescence probes. The critical micelle concentrations (cmc's), effective carbon atom numbers (neff's), hydrophilic-lipophilic balances (HLBs), mean micelle aggregation numbers, micropolarities, and microviscosities of these surfactant micelles have been determined. The logarithmic cmc of the alkylnaphthalene sulfonates decreases linearly with an increase in the neff. The logarithmic aggregation number of the alkylnaphthalene sulfonates increases linearly with an increase in the neff. However, in contrast to the alkylsufonates and the alkylbenzene sulfonates, the aggregation for these alkylnaphthalene sulfonate molecules is less sensitive to the increase in the neff. The micropolarity of these alkylnaphthalene sulfonate micelles is less sensitive to the increase in the alkyl chain length and is lower than that of sodium dodecyl sulfate (SDS). The microviscosity of these alkylnaphthalene sulfonate micelles increases with an increase in the alkyl chain length and is lower than those of nonionic surfactants and zwitterionic surfactants. These results suggest that naphthyl rings have a notable effect on the micellization of SANS.     

相对分子质量对烷基芳基磺酸盐复配体系固液吸附性能的影响

测定了5种平均相对分子质量和相对分子质量(以下简称分子量)分布不同的烷基芳基磺酸盐复配体系的吸附等温线,分别考察了分子量、分子量分布、温度和无机盐对复配体系在油砂/石英砂表面的吸附量的影响。 结果表明,对5种分子量分布复配体系吸附量依次降低的顺序为递增分布、正态分布、反正态分布、递减分布和均匀分布;复配体系在油砂表面的吸附量随着磺酸盐的平均分子量的增大而增大,随温度的升高而降低,随NaCl浓度的增加而增加。另外,在低浓度时,MgCl2、CaCl2和Na2SO4比NaCl对吸附的影响显著。 NaCl对复配体系在油砂表面的吸附影响比对石英砂表面吸附的影响略大。     

结构及助剂对十五烷基芳基磺酸盐吸附性能的影响

在45 ℃下,采用两相滴定法测定了4种自制高纯度十五烷基芳基磺酸盐在油砂上的吸附等温线。 分别考察了表面活性剂浓度、NaCl、NaOH、NaHCO3、正丁醇浓度及分子结构对表观吸附量的影响。 结果表明,随着磺酸盐浓度的增大,吸附量先增大后有所降低。 NaCl和NaOH的加入使吸附量增大,NaHCO3及正丁醇的加入使吸附量降低,且随着芳基位置向长烷基链中间的移动,吸附量降低,受助剂的影响变小。     

Diphenyl disulfide and sodium in NMP as an efficient protocol for in situ generation of thiophenolate anion: selective deprotection of aryl alkyl ethers and alkyl/aryl esters under nonhydrolytic conditions

Aryl methyl ethers, methyl esters, aryl esters, and aryl sulfonates are chemoselectively deprotected under nonhydrolytic conditions by treatment with Ph(2)S(2) (0.6 equiv) and Na (1.6 equiv) in NMP under reflux or at 90 degrees C. Quantitative utilization of the 'PhS' moiety as the effective nucleophilic species represents conservation of atom economy. Other solvents such as HMPA, DMPU, DMEU, and DMF afforded comparable results. Chloro, nitro, aldehyde, alpha,alpha-diketone, and alpha,beta-unsaturated ketone functionalities remain unaffected. The deprotection was found to take place in the order aryl ester > alkyl ester > aryl alkyl ether. Substrates bearing strong electron-withdrawing groups react at a faster rate than those not having such substitution. The differences in rate of reaction has been exploited for selective deprotection for intramolecular competition. An aryl acetate/benzoate is deprotected selectively in preference to a methyl ester or aryl methyl ether. Selective deprotection of a methyl ester is observed in the presence of an aryl alkyl ether.     

Zn/CuI-mediated coupling of alkyl halides with vinyl sulfones, vinyl sulfonates, and vinyl sulfonamides

A novel high-yielding Zn/CuI-mediated coupling method of alkyl halides with vinyl sulfones, vinyl sulfonates, and vinyl sulfonamides is described. This protocol is applicable for primary, secondary, and tertiary alkyl iodides and bromides. Alkyl chlorides and aryl and vinyl halides were unreactive under the reaction conditions. Formamide was found to be a superior solvent for obtaining high yields.     

Thermodynamic properties of micellization of Sulfobetaine-type Zwitterionic Gemini Surfactants in aqueous solutions--a free energy perturbation study

In this article, the validity and accuracy of the free energy perturbation (FEP) model used in a previous article for ionic liquid-type Gemini imidazolium surfactants (ILGISs) is further evaluated by using it to model the Enthalpy-entropy compensation of Sulfobetaine-type Zwitterionic Gemini Surfactants (SZGSs), with different carbon atoms of the hydrophobic group or the spacer chain length, in aqueous solutions. In the FEP model, the Gibbs free energy contributions to the driving force for micelle formation are computed using hydration data obtained from molecular dynamics simulations. According to the pseudo-phase separation model, the thermodynamic properties of micellization in aqueous solutions for SZGS were discussed. The results show that the micellization of SZGS in aqueous solutions is a spontaneous and entropy-driven process. It is linearly Enthalpy-entropy compensated and different from the micelle formation of ILGIS but similar to anionic surfactants. The compensation temperature was found to be (302±3)K which was lower than ILGIS. As the temperature rises, the micellization is easy initially but then becomes difficult with the unusual changes of enthalpy values from positive to negative. The contribution of entropy change to the micellization tends to decrease but the contribution of enthalpy change tends to increase. In particular, as the number carbon atoms in the alkyl chains and spacer chains are increased, the thermodynamic favorability and stability of the micelles both increase.