C12-s-C12•2Br和己醇混合水溶液的胶团化行为

己醇的加入使C12-s-C12•2Br（s=3,4,6）的临界胶团浓度cmc降低,s越大其影响也越显著.己醇参与组成了混合胶团,当添加的己醇量相同时,它在混合胶团中的摩尔分数几乎一样.混合胶团表面反离子解离度随己醇浓度增大而增大.     

最大泡压法研究C12-2-Ex-C12•2Br在气/液表面的吸附动力学

用最大泡压法考察季铵盐Gemini表面活性剂C₁₂-2-E_x-C₁₂?2Br (x＝1, 2, 3)在气/液表面吸附动力学行为, 研究表明增加表面活性剂体相浓度和温度将加快分子扩散速度, 因此提高了表面吸附的动力学效果. 增加联接链长度x减小了分子预聚集倾向, 溶液中的单分子浓度增加, 有利于初始扩散, 使γ_t降低. 接近饱和吸附时, 由于x较大的单元分子在表面层占据的截面积也较大, 降低了表面层甲基端基的覆盖度, 相对升高了介平衡表面张力. 与对应的同头基同碳原子数的十二烷基三甲基溴化铵(C₁₂TABr)比较, C₁₂-2-E₁-C₁₂?2Br分子更倾向于吸附在表面层上.     

Micellization of monomeric and dimeric (gemini) surfactants in polar nonaqueous-water-mixed solvents

Dimeric or gemini surfactants are novel surfactants that are finding a great deal of discussion in the academic and industrial arena. They consist of two hydrophobic chains and two polar head groups covalently linked by a spacer. Data on critical micelle concentration (cmc) and degree of counterion dissociation (α) are reported on bis-cationic C₁₆H₃₃N⁺(CH₃)₂–(CH₂)_s–N⁺(CH₃)₂C₁₆H₃₃, 2Br⁻, referred to as 16-s-16, for spacer lengths s=4, 5, 6 in aqueous and in polar nonaqueous (1-propanol, 2-methoxyethanol or methyl cellosolve, dimethyl sulfoxide, acetonitrile)-water-mixed solvents. The behavior is compared with conventional monomeric surfactant cetyltrimethylammonium bromide (CTAB). Thermodynamic parameters are obtained from the temperature dependence of the cmc values. It is observed that micellization tendency of the surfactants decreases in the presence of polar nonaqueous solvents. However, detailed studies with dimethylsulfoxide (DMSO) show that the geminis nearly outclass the micellization-arresting property of this solvent. Also, within geminis, higher spacer length is found suitable for showing micellization even with high DMSO content (50% v/v). The implications of these results of gemini micellization may be useful in micellar catalysis in polar nonaqueous solvents.     

C12-s-C12•2Br和C12En混合水溶液的胶团化行为

季铵盐二聚表面活性剂C12 s C12•2Br（s=2、3、4、6）和非离子表面活性剂C12E10或C12E23在水溶液中生成混合胶团.其临界胶团总浓度cmcT值介于二元复配体系中各组分的临界胶团浓度和之间.当添加少量非离子型表面活性剂（在水溶液中的摩尔分数α2=0.1）时,混合胶团中C12E10或C12E23的摩尔分数均已超过0.35;随着溶液中非离子型表面活性剂含量的增大,混合胶团中逐渐以C12E10或C12E23成分为主.     

16-n-16型双子表面活性剂稳定纳米金的制备及其催化性能

双子表面活性剂由于其特殊的两亲结构可以作为纳米金颗粒(AuNPs)的表面稳定剂,但双子表面活性剂结构中的连接基团对AuNPs的粒径大小及稳定性有显著影响。本文制备了16-n-16(n=2,3,4和6)型双子表面活性剂稳定的金纳米溶胶,考察了体系pH对AuNPs稳定性的影响,并测试了其对4-硝基苯酚加氢还原体系的催化效果。结果表明,16-4-16和16-3-16对AuNPs的稳定性效果较好,所制备的AuNPs中,16-3-16-AuNPs在不同pH的环境中稳定性最好,而16-4-16-AuNPs在4-硝基苯酚加氢还原反应中的催化活性最佳。     

Micellization and adsorption of a zwitterionic surfactant: N-dodecyl betaine-effect of salt

Time-resolved fluorescence quenching, self-diffusion measurements and calorimetric investigations have been used in order to investigate the effect of salt on aggregation in aqueous solutions and the adsorption onto silica gel of the zwitterionic surfactant N-dodecyl betaine (NDB).

The micelle aggregation number of NDB stays constant when the NDB or salt concentration increases but decreases with an increase of temperature. Evidence is presented for the binding of cations and anions to micellar aggregates. The degree of binding has been obtained for Na⁺, Ca²⁺ and Cl⁻ ions; it is always larger for the anion.

Enthalpies of micellization were obtained directly from calorimetric curves of NDB in dilution experiments. The observed decrease of the endothermic enthalpies of micellization with increasing temperature or salinity is attributed to a structural change in the water molecules around the alkyl chain of the free monomers.

The adsorption isotherms of NDB onto silica gel depend very little on temperature, and a plateau is reached near the CMC. At saturation, the adsorbed amount of NDB depends on the salt and follows the sequence NDB < (NDB + NaCl) < (NDB + CaCl₂).

The exothermic differential molar enthalpies of adsorption demonstrate the same behaviour as the enthalpies of micellization with varying temperature or salinity. Adsorption onto silica gel depends on the NDB concentration, the salt concentration and temperature.     

C12-s-C12·2Br和己醇混合水溶液的胶团化行为

己醇的加入使C12-s-C12·2Br(s=3,4,6)的临界胶团浓度cmc降低,s越大其影响也越显著.己醇参与组成了混合胶团,当添加的己醇量相同时,它在混合胶团中的摩尔分数几乎一样.混合胶团表面反离子解离度随己醇浓度增大而增大.     

含对苯氧基联接链的羧酸盐Gemini表面活性剂合成及胶团化特性

合成了含对苯氧基联接链的羧酸盐Gemini表面活性剂,研究了其胶团化特性.结果表明,该羧酸盐Gemini表面活性剂具有很低的cmc值,给出了cmc-T(温度)以及lncmc-(m+1)(烷烃链长)的回归方程.计算了胶团化的热力学函数变化,证实胶团化过程来自熵驱动,并表现出焓/熵补偿现象,在所考察的系列中,以(m+1)=11的胶团最为稳定.     

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.     

Excess volumes of the binary mixtures 1,2-dichloroethane ? n -alkanols [C2?C6]

Volume changes on mixing of binary systems formed by 1,2-dichloroethane andn-alcohols, namely, ethanol,n-propanol,n-butanol,n-pentanol andn-hexanol were measured as a function of composition at 30, 35, 40 and 45 °C. At all compositions theV ^E values are all positive for all systems. The molar excess volumes of mixing for equimolar mixtures increase as the length of carbon chain increases.V ^E becomes more positive on increasing temperature. The positive value of the excess volume has been attributed to breaking of hydrogen bonds of associated species of alcohol by dilution with 1,2-dichloroethane.     

Micellization and applications of narrow-distribution poly[2-(dimethylamino)ethyl methacrylate]

Oxyanion-initiated polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA), initiated by potassium benzyl alcoholate (BzOK), produced a number of well-defined, water-soluble benzyloxy end-capped homopolymers of various molecular weights. The structure of these homopolymers was confirmed by FTIR and ¹H NMR. The molecular weights of the polymers were estimated by comparing the ¹H NMR peak integrals for phenyl protons of the benzyloxy group with those of the dimethylamino protons of the monomeric unit. GPC analysis showed that these homopolymers possess a narrow molecular weight distribution ( ) in the range of 1.15–1.28. Under acidic or neutral conditions, the polymers exhibit the behavior of polymeric surfactants bearing protonized tertiary amines in their pendants, with critical micelle concentration (CMC) between 0.5 to 1 g/L and surface tension dropping below 40 mN/m. It was also found that the lower critical solution temperature (LCST) of the polymeric surfactants (as determined by UV-visible spectroscopy) varied with properties such as molecular weight, concentration, and pH in aqueous media. The polymeric surfactants showed excellent pH-response and emulsifier properties when used in the emulsion polymerization of styrene.     

界面扩张流变法研究C12mimBr对Gemini12-2-12在空气/水界面聚集行为的影响

采用界面扩张流变技术研究了季铵盐偶联表面活性剂C₁₂-(CH₂)₂-C₁₂·2Br (Gemini12-2-12)及其与离子液体表面活性剂溴化1-十二烷基-3-甲基咪唑(C₁₂mimBr)复配体系的动态界面张力、扩张流变性质和界面弛豫过程等, 探讨了C₁₂mimBr 对C₁₂mimBr/Gemini12-2-12 混合体系界面性质的影响及C₁₂mimBr 对Gemini12-2-12界面聚集行为影响的机制. 结果表明, 随着离子液体表面活性剂的不断引入, 体系界面吸附达到平衡所需的时间逐渐缩短, 扩张模量和相角明显降低, 界面吸附膜由粘弹性膜转变为近似纯弹性膜; 同时, 界面及其附近的弛豫过程也发生显著变化, 慢弛豫过程消失, 快弛豫过程占主导地位, 且离子液体浓度越高, 快弛豫的贡献越大. 这些界面性质的变化主要归因于离子液体表面活性剂C₁₂mimBr参与界面形成及两表面活性剂在界面竞争吸附的结果. 少量离子液体表面活性剂C₁₂mimBr 的加入可以填补疏松的Gemini12-2-12 界面上的空位, 形成混合界面吸附膜. 随着C₁₂mimBr 含量的增加, 嵌入界面的C₁₂mimBr 分子数不断增多, 导致界面上相互缠绕的Gemini12-2-12烷基链“解缠”, 在体相和界面分子扩散交换的过程中“解缠”的Gemini12-2-12分子从界面上解吸回到体相, 与此同时, C₁₂mimBr 分子相对较小的空间位阻及较强的疏水作用促使其优先扩散至界面进而取代Gemini12-2-12分子, 最终界面几乎完全被C₁₂mimBr分子所占据.     

Micellar-catalyzed alkaline hydrolysis of 2,4-dinitrochlorobenzene in a cationic gemini surfactant

Micellar-catalyzed alkaline hydrolysis of 2,4-dinitrochlorobenzene (DNCB) in the presence of a conventional cationic surfactant CTAB or a cationic gemini surfactant 1,2-ethane bis(dimethyldodecylammonium bromide) (12-2-12) were studied spectrophotometrically at 25 °C. It was found that both CTAB and 12-2-12 micelles accelerated the alkaline hydrolysis of DNCB, and the binding constant of the substrate to the micelle, K_S, for 12-2-12 (K_S = 310 M⁻¹) was larger than that for CTAB (85 M⁻¹), which suggested that DNCB molecules bound with gemini micelles more easily than with CTAB. However, the second-order rate constant in micellar pseudophase (k_M = 1.22 × 10⁻³ s⁻¹) for 12-2-12 was lower than k_M for CTAB (4.01 × 10⁻³ s⁻¹) because the substrate may enter the interior of the 12-2-12 micelles. It was found also that 12-2-12 had a similar catalysis mechanism to CTAB when the concentration of 12-2-12 was relatively low (ca. <5 mM). However, above this concentration, higher microviscosity and significant increases in aggregation number and micelle size with increased surfactant concentration may remarkably influence the hydrolysis reaction.     

Crystal structures of [Rh(η-C5H5)(C3S5)] and [Rh(η-C5Me5)(C3S5)]2 and properties of their oxidized species

[Rh(η⁵-C₅H₅)(C₃S₅)] and [Rh(η⁵-C₅Me₅)(C₃S₅)]₂ [C₃S₅²⁻=4,5-disulfanyl-1,3-dithiole-2-thionate(2-)] were prepared by reactions of [NMe₄]₂[C₃S₅] with [Rh(η⁵-C₅H₅)Cl₂]₂ and [Rh(η⁵-C₅Me₅)Cl₂]₂, respectively. Their X-ray crystal structural analyses revealed a monomeric form for the former complex and a dimeric geometry containing bridging S-Rh-S bonds for the latter in the solid state. They were reacted with bromine to afford [RhBr(L)(C₃S₅)] (L=η⁵-C₅H₅ and η⁵-C₅Me₅) with the Rh-Br bond and one electron-oxidation on the C₃S₅ ligand. ESR spectra and spin densities for these oxidized species are discussed.     

Micellization behaviour and thermodynamic parameters of 12-2-12 gemini surfactant in (water + organic solvent) mixtures

The effect of organic solvents on micellization behaviour and thermodynamic parameters of a cationic gemini (dimeric) surfactant, C₁₂H₂₅(CH₃)₂N⁺–(CH₂)₂–N⁺(CH₃)₂C₁₂H₂₅·2Br^?, (12-2-12) was studied in aqueous solutions over the range of T = (293.15 to 323.15) K using the conductometric technique. Ethylene glycol (EG), dimethylsulfoxide (DMSO) and 1,4-dioxan (DO) were used as organic solvents with three different contents. The critical micelle concentration (cmc) and the degree of counter ion dissociation (α) of micelles in the water and in the (water + organic solvent) mixtures including 10%, 20%, and 30% solvent contents were determined. The standard Gibbs free energy $(\mathrm{\Delta }{G}_{\text{m}}^{°})$, enthalpy $(\mathrm{\Delta }{H}_{\text{m}}^{°})$ and entropy $(\mathrm{\Delta }{S}_{\text{m}}^{°})$ of micellization were estimated from the temperature dependence of the cmc values. It was observed that the critical micelle concentration of the gemini surfactant and the degree of counter ion dissociation of the micelle increased as the volume percentage of organic solvent, and temperature increased. The standard Gibbs free energy of micellization was found to be less negative with the increase in the organic solvent content and temperature.     

Strong effect of NaBr on self-assembly of quaternary ammonium gemini surfactants at air/water interface and in aqueous solution studied by surface tension and fluorescence techniques

The effects of NaBr on the adsorption of alkanediyl-bis-(dimethyl dodecyl- ammonium bromide) (referred to as C₁₂-s-C₁₂ 2Br) at the air/water interface and on the micellization in the solution have been investigated by surface tension and fluorescence techniques. The results showed that the addition of NaBr greatly enhances their efficiency and effectiveness in surface tension reduction as well as the ability of micellization, even induces strong premicellar aggregation before the cmc. These were attributed to the unique molecular structure of gemini surfactant, where the flexible polymethylene chain was the spacer linking the two quaternary ammonium heads. By a short spacer, the charges of the two quaternary ammonium head groups are concentrated. Even for a long spacer (s = 12), since it is bent toward the alkyl tails, the similar effect is also produced. This results in the high sensitivity of their ionic head groups to salt. Besides, the addition of salt also effectively promotes the hydrophobic interaction between the alkyl tails of gemini surfactants. The addition of NaBr strongly promotes the adsorption of quaternary ammonium gemini surfactants C₁₂-s-C₁₂ 2Br at the air/water interface and the micellization in the solution.     

Complexes of titanium and zirconium based on [C5Me4CH2-(2-C5H4N)] ligand

Half-sandwich [η⁵:η¹-κN-C₅Me₄CH₂-(2-C₅H₄N)]MCl₃ (M = Ti (4), Zr (5)) and sandwich [η⁵-C₅Me₄CH₂-(2-C₅H₄N)][η⁵-C₅Me₅]ZrCl₂ (6) ring-peralkylated complexes have been prepared and characterized. Evidence of the intramolecular coordination of the side-chain pyridyl group both in 4 and 5 in solutions is provided by NMR spectroscopy data. Crystal structure of an adduct 5-py with one molecule of pyridine has been established by X-ray diffraction analysis.     

Applications of cationic gemini surfactant in preparing multi-walled carbon nanotube contained nanofluids

Stable homogeneous nanofluids of multi-walled carbon nanotubes (MWNTs) were prepared by using gemini cationic surfactant trimethylene-1,3-bis (dodecyldimethyl ammonium bromide), abbreviated as 12-3-12,2Br⁻¹, as dispersing agents. Zeta potential and FT-IR measurements were employed to investigate the adsorption mechanism of 12-3-12,2Br⁻¹ on MWNTs. The interactions between MWNTs and 12-3-12,2Br⁻¹ through hydrophobic segments cause hydrophilic MWNT-suspended medium interfaces with high positive charges, which enables the nanofluids to be stable for long periods. At relatively low temperatures the superfluous surfactant molecules form stable layer or column micelles, making an increase in the viscosity of nanofluids. Only 0.6 wt% gemini surfactant was used to obtain 0.5 wt% MWNT dispersions. The dispersions show no MWNTs precipitation for at least 5 weeks.     

Synthesis and structures of triphenylbismuth diaroxides Ph3Bi(OAr)2, Ar = C6H3(Br2-2,4), C6H2(Br2-2,6)(NO2-4), and C6H2[(NO2)3-2,4,6]

Triphenylbismuth diaroxides Ph₃Bi(OAr)₂ (Ar = C₆H₃(Br₂-2,4) (I), C₆H₂(Br₂-2,6)(NO₂-4) (II), and C₆H₂[(NO₂)₃-2,4,6] (III) are synthesized in yields up to 74% by the reaction of triphenylbismuth with phenols in the presence of hydrogen peroxide (taken at a molar ratio 1: 2: 1, respectively) in ether. According to X-ray diffraction data, the bismuth atoms in compounds I-III have distorted trigonal-bipyramidal coordination with the aroxyl substituents in the axial positions; the Bi-C, Bi-O bond lengths and the OBiO, CBiC angles vary in the intervals 2.162–2.204, 2.150–2.299 ? and 172.4°–176.1°, 109.6°–139.9°, respectively. Compound II exhibits intramolecular contacts between the central atom and ortho-Br atoms (3.924, 4.101 ?), and compound III has similar contacts of the Bi atom with the O atoms of the ortho-nitro groups (3.114, 3.313 ?). Original Russian Text ? V.V. Sharutin, I.V. Egorova, O.K. Sharutina, A.P. Pakusina, M.A. Pushilin, 2007, published in Koordinatsionnaya Khimiya, 2007, Vol. 33, No. 1, pp. 14–21.