聚醚型表面活性剂水溶液中胶团的生成

属于ABA型嵌段共聚物(A为聚氧乙烯,B为聚氧丙烯)的聚醚型表面活性剂分子在水中是否生成胶团,文献报道的结果迥异,临界胶团浓度值随测定方法不同出入很大.某些AB型或ABA型嵌段共聚物在选择性有机溶剂中表现出异常胶团化行为,但对于水体系迄今未见报道.本文以多种实验手段研究了典型的聚醚型表面活性剂Pluronic L-64水溶液的胶体与表面性质.结果表明,与通常的表面活性剂不同,随着温度或浓度的变化,L-64溶液中生成单分子胶团或者缔合胶团.在两者的转变间,首次观察到了水体系中的异常胶团化现象.     

Threadlike micelle formation of anionic surfactants in aqueous solution

We have investigated the formation of threadlike micelles consisting of anionic surfactants and certain additives in aqueous solution. Threadlike micelles long enough to be entangled with each other were formed in a clear aqueous solution of two anionic surfactants, sodium hexadecyl sulfate and sodium tetradecyl sulfate. These solutions also contained pentylammonium bromides or p-toluidine halides and exhibited remarkable viscoelasticity. Because the molar ratio of surfactants to cationic additives in these micelles seemed close to unity, they formed 1:1 stoichiometric complexes between surfactant anions and additive cations, as previously found in systems of cationic surfactants such as hexadecyltrimethylammonium bromide and sodium salicylate. The viscoelastic behavior of these anionic threadlike micellar systems was adequately described by a simple Maxwell element with a single relaxation time and strength, as in many similar cationic systems.     

Anionic hybrid threadlike micelle formation in an aqueous solution

Novel anionic hybrid threadlike micelle formation was found in an aqueous solution of an anionic surfactant, sodium tetradecylsulfate (NaC(14)S), and partially quarternized polyelectrolyte at ca. 0.55, poly(N,N-diallyl-N-methylamine-ran-N,N-diallyl-N-ethyl-N-methylammonium bromide) (P(DAM/DAEMBr)). The system precipitated insoluble complexes at a composition of iso-electric points, forming long and stable hybrid threadlike micelles at a composition close to an iso-molar point between NaC(14)S and P(DAM/DAEMBr) in monomer units. Then, the system turned into transparent liquids and showed remarkable viscoelasticity due to entanglements between the formed anionic hybrid threadlike micelles.     

Aggregation and micelle formation of ionic liquids in aqueous solution

Association of ionic liquids possessing n-octyl moiety either in the cation or in the anion has been studied in aqueous solution with conductivity and turbidity measurements as well as using 2-hydroxy-substituted Nile Red solvatochromic probe. 1-Butyl-3-methylimidazolium octyl sulfate was found to act as a surfactant above 0.031 M critical micelle concentration. In contrast, 1-methyl-3-octylimidazolium chloride produced inhomogeneous solution of larger aggregates, which were dissolved on the addition of more than 2:1 molar excess of sodium dodecyl sulfate (SDS) due to mixed micelle formation. Even small amount (<10 mM) of ionic liquids could markedly reduce the polarity of the Stern layer of SDS micelle.     

Characterization of micelle formation of dodecyldimethyl-N-2-phenoxyethylammonium bromide in aqueous solution

Aggregation behavior of dodecyldimethyl-N-2-phenoxyethylammonium bromide commonly called domiphen bromide (DB) was studied in aqueous solution. The Krafft temperature of the surfactant was measured. The surfactant has been shown to form micellar structures in a wide concentration range. The critical micelle concentration was determined by surface tension, conductivity, and fluorescence methods. The conductivity data were also employed to determine the degree of surfactant counterion dissociation. The changes in Gibb's free energy, enthalpy, and entropy of the micellization process were determined at different temperature. The steady-state fluorescence quenching measurements with pyrene and N-phenyl-1-naphthylamine as fluorescence probes were performed to obtain micellar aggregation number. The results were compared with those of dodecyltrimethylammonium bromide (DTAB) surfactant. The micelle formation is energetically more favored in DB compared to that in DTAB. The 1H-NMR spectra were used to show that the 2-phenoxyethyl group, which folds back onto the micellar surface facilitates aggregate formation in DB.     

Fourier transform infrared spectra and micelle formation of sodiumn-alkanesulfonates in aqueous solution

The concentration dependences of the Fourier transform infrared spectra of aqueous solutions of sodiumn-pentanesulfonate,n-hexanesulfonate,n-heptanesulfonate, andn-octanesulfonate were studied in concentration ranges encompassing the critical micellization concentrations (c.m.c). Changes in wavenumber, bandwidth, and intensity of infrared absorption bands were used to monitor the changes in molecular association with concentration. The premicellar aggregation below the c.m.c. may accompany the association of the alkyl chain, but not the counter-ion binding with the SO ₃ ^– group. Above the c.m.c, the front location of the counter-ion against the SO ₃ ^– group at the micelle surface is demonstrated.     

Surface adsorption and micelle formation of surface active ionic liquids in aqueous solution

Aqueous solutions of three kinds of surface active ionic liquids composed of the 1-alkyl-3-methylimidazolium cation have been investigated by means of surface tension and electrical conductivity measurements at room temperature (298 K). The surface tension measurements provided a series of parameters, including critical micelle concentration (cmc), surface tension at the cmc (gammacmc), adsorption efficiency (pC20), and effectiveness of surface tension reduction (Picmc). In addition, with application of the Gibbs adsorption isotherm, maximum surface excess concentration (Gammamax) and minimum surface area/molecule (Amin) at the air-water interface were estimated. The effect of sodium halides, NaCl, NaBr, and NaI, on the surface activity was also investigated. It was found that both the pC20 and the Picmc were rather larger than those reported for traditional ionic surfactants and the cmc values were somewhat lower than those for typical cationic surfactants, alkyltrimethylammonium bromides, and comparable to typical anionic surfactants, sodium alkyl sulfates. These results demonstrate that the surface activity of long-chained imidazolium IL is somewhat superior to that of conventional ionic surfactants.     

Wormlike micelle formation and flow alignment of a pluronic block copolymer in aqueous solution

The self-assembly into wormlike micelles of a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer Pluronic P84 in aqueous salt solution (2 M NaCl) has been studied by rheology, small-angle X-ray and neutron scattering (SAXS/SANS), and light scattering. Measurements of the flow curves by controlled stress rheometry indicated phase separation under flow. SAXS on solutions subjected to capillary flow showed alignment of micelles at intermediate shear rates, although loss of alignment was observed for high shear rates. For dilute solutions, SAXS and static light scattering data on unaligned samples could be superposed over three decades in scattering vector, providing unique information on the wormlike micelle structure over several length scales. SANS data provided information on even shorter length scales, in particular, concerning "blob" scattering from the micelle corona. The data could be modeled based on a system of semiflexible self-avoiding cylinders with a circular cross-section, as described by the wormlike chain model with excluded volume interactions. The micelle structure was compared at two temperatures close to the cloud point (47 degrees C). The micellar radius was found not to vary with temperature in this region, although the contour length increased with increasing temperature, whereas the Kuhn length decreased. These variations result in an increase of the low-concentration radius of gyration with increasing temperature. This was consistent with dynamic light scattering results, and, applying theoretical results from the literature, this is in agreement with an increase in endcap energy due to changes in hydration of the poly(ethylene oxide) blocks as the temperature is increased.     

Electrical conductivity study on micelle formation of long-chain imidazolium ionic liquids in aqueous solution

Electrical conductivity was measured for aqueous solutions of long-chain imidazolium ionic liquids (IL), 1-alkyl-3-methylimidazolium bromides with C(12)-C(16) alkyl chains. The break points appeared in specific conductivity (kappa) vs concentration (c) plot indicates that the molecular aggregates, i.e., micelles, are formed in aqueous solutions of these IL species. The critical micelle concentration (cmc) determined from the kappa vs c plot is somewhat lower than those for typical cationic surfactants, alkyltrimethylammonium bromides with the same hydrocarbon chain length. The electrical conductivity data were analyzed according to the mixed electrolyte model of micellar solution, and the aggregation number, n, and the degree of counter ion binding, beta, were estimated. The n values of the present ILs are somewhat smaller than those reported for alkyltrimethylammonium bromides, which may be attributed to bulkiness of the cationic head group of the IL species. The thermodynamic parameters for micelle formation of the present ILs were estimated using the values of cmc and beta as a function of temperature. The contribution of entropy term to the micelle formation is superior to that of enthalpy term below about 30 degrees C, and it becomes opposite at higher temperature. This coincides with the picture drawn for the micelle formation of conventional ionic surfactants.     

Investigation of micelle formation by fluorescence correlation spectroscopy

We show that noncovalently bound dye molecules can be used as labels in single-molecule fluorescence experiments for the determination of aggregate formation in standard surfactant systems. Aqueous solutions of sulfosuccinic acid bis(2-ethylhexyl) ester sodium salt, hexadecyltrimethylammonium chloride, and pentaethylene glycol monododecyl ether have been studied by fluorescence correlation spectroscopy using commercially available dyes. The translational diffusion coefficient and the critical micelle concentrations have been determined and compare well to values reported in the literature. The respective charges of the surfactant and of the dye molecule are crucial for the effectiveness of the presented method.     

Detection of alcohols in gas chromatographic effluent by laser-light scattering

A laser-light-scattering detector that is sensitive to alcohols has been developed for gas chromatography. The detector consists of a miniature concentric nebulizer that uses a cold atomization gas and an Ar⁺ laser. Calibration curves for the alcohols exhibit characteristic sigmoidal shapes. Signal-to-noise ratios were optimized by examining the photomultiplier tube temperature, collection wavelength and detection scheme (i.e., photon counting vs. direct current detection). Limits of detection for five test alcohols were in the 2–8 μg/s range.     

A pressure and temperature study on solubility and micelle formation of sodium perfluorodecanoate in aqueous solution

Both the critical solution temperature (CST, or the Krafft temperature) and the critical solution pressure (CSP, or the Tanaka pressure) were determined for sodium perfluorodecanoate (NaPFDe) in water, and the result shows that the Krafft temperature is raised with the increase in the Tanaka pressure. A thermodynamic analysis has been made on the data for the critical micellization concentration (cmc) and of the solubility at various temperatures and pressures. The estimated change in the partial molal volume, resulting from micelle formation from the singly dispersed state and from the hydrated solid state, was found to be conspicuously higher for NaPFDe compared to hydrocarbon surfactants. This has been ascribed to the more pronounced role of carbon chain-water interactions and water structure effects of the fluorocarbon surfactants.     

pH Responsivity and micelle formation of gradient copolymers of methacrylic acid and methyl methacrylate in aqueous solution

A series of gradient copolymers of methacrylic acid (MAA)/methyl methacrylate (MMA) with four end-to-end composition profiles (uniform, linear gradient, triblock with linear gradient midblock, and diblock) but all having an average chain composition of ?F(MMA) ≈ 0.5 and an average chain length of 200 were synthesized via model-based, computer-programmed, semibatch atom-transfer radical copolymerization (ATRcoP). These samples allowed us to investigate systematically the effects of the gradient composition profile on the pH responsivity and micelle formation of the copolymers in an aqueous solution. Measurements included light transmittance, TEM, AFM, DLS, (1)H NMR, and pH titration. It was found that linear gradient, triblock, and diblock copolymers formed spherical micelles at high pH. The micelles of the linear gradient copolymer contained MMA units in their hydrophilic shells, and those of the triblock and diblock copolymers had all of their MMA units residing in their cores. The composition profile showed a strong effect on the degree of acid dissociation at a given pH. The conformational transition of the copolymer chains was determined by both the pH value and composition profile. Copolymers having sharper gradients required a lower pH to trigger the conformational transition and a narrower pH range to complete the transition.     

Micelle formation by N-alkyl-N-methylpyrrolidinium bromide in aqueous solution

The micellization of the ionic liquid N-alkyl-N-methylpyrrolidinium bromide (C(n)MPB, n = 12, 14 and 16) in aqueous solutions was investigated by surface tension measurements, electrical conductivity and static luminescence quenching. The effectiveness of the surface tension reduction (Π(cmc)), maximum surface excess concentration (Γ(max)) and the minimum area (A(min)) occupied per surfactant molecule at the air/water interface can be obtained from the surface tension measurements at 25 °C. The critical micelle concentration (cmc) at different temperatures and a series of thermodynamic parameters (ΔG, ΔH and ΔS) of micellization were evaluated from electrical conductivity measurements in the temperature range of 25-45 °C. The thermodynamic parameters show that the micelle formation is entropy-driven at low temperature and enthalpy-driven at high temperature. Furthermore, the micelle aggregation number (N(agg)) of C(n)MPB was calculated according to the Turro-Yekta method through static luminescence quenching and found that N(agg) (49, 55, and 59) increased with the hydrophobic chain length of C(n)MPB.     

Volumetric behavior and micelle formation of aqueous surfactant mixtures

A thermodynamic treatment of the volumetric behavior of surfactant mixtures in water have been developed on the basis of the thermodynamic treatment of mixed micelle by Motomura et al. Densities of aqueous solutions of mixtures of decyltrimethylammonium bromide (DeTAB) and dodecyltrimethylammonium bromide (DTAB) have been measured as a function of total molality at constant compositions. The apparent molar volumes of the mixtures have been derived from the density data and the mean partial molar volume of monomeric surfactant mixture V _t ^w , the molar volume of mixed micelle V^M/N _t ^M , the voluem of formation of mixed micelle _W ^M V, and the composition of surfactant in the mixed micelle have been evaluated. The V _t ^W , V^M/N _t ^M , and _W ^M V have been observed to depend on the composition. The linear dependence of V _t ^W and V^M/N _t ^M on the composition indicates that the mixing of DeTAB and DTAB is ideal both in the monomeric and micellar states. This has been confirmed further by the shape of the critical micelle concentration vs. composition curves.     

十二烷基硫酸钠与溴化正辛基三甲基铵混合表面活性剂水溶液的表面吸附及胶团形成

本文研究了盐存在时不同比例的十二烷基硫酸钠(简称12CH)和溴化正辛基三甲基铵(简称C8NBr)混合物的表面活性、表面吸附以及胶团形成等性质,结果表明:(1)正、负离子表面活性剂混合物具有很高的表面活性,不论其混合比例如何,临界胶团浓度(cmc)及cmc时溶液的表面张力(γcmc)皆较任何单一组分时小;(2)不论体相中比例如何,表面层中12CH和C8NBr的饱和吸附量的摩尔比皆～1.7且总饱和吸附量亦皆～5.2x10[-10]mol.cm[-2].由此求得表面层中分子截面积为32A[2],与由分子结构计算的数据相近,说明正、负表面活性离子排列紧密;(3)与碳链长相同的正、负离子型表面活性剂混合水溶液比较,本体系反应离子浓度对cmc有明显影响,证实表面层带电,胶团也带电;(4)计算了离子强度相同,温度不同时和温度相同、离子强度不同时的热力学量,得出离子强度大者易形成胶团。     

Calorimetric determination of the enthalpy of micelle formation in aqueous media

The enthalpy of micelle formation of ionic surfactants in aqueous solutions with varying concentration of additives (i. e. NaCl. alcohols) was measured by using a very sensitive microcalorimeter. The heats of dilution were measured from concentrations below the c.m.c. to above c.m.c. This enables one to detect the aggregation process around the c.m.c. region, an analysis hitherto not extensively reported in the current literature. The effect of electrolyte addition on micellar enthalpy is discussed, as compared to the addition of short chain alcohols.     

Dynamic light scattering from micelle complexes of cetyltrimethylammonium bromide-sodium salicylate in aqueous solutions

The diffusion coefficient of cetyltrimethylammonium bromide-sodium salicylate in aqueous solutions has been determined, using the dynamic light-scattering technique, as a function of sodium salicylate concentration, as well as of temperature. Using a gel model the results are discussed in terms of intermicellar pseudo-linkages, entanglements of threadlike micelles, and formation of pseudo-network.     

Studies on solvophobic interactions and micelle formation in non aqueous solvents

Micelle formation of various surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate has been studied in organic solvents of various dielectric constants and intermolecular H-bonding capability, viz. molten acetamide, N-methyl acetamide (NMA) and N,N-dimethyl acetamide (DMA), at different temperatures by electrical conductivity and surface tension methods. Both methods show that micelles are formed in acetamide, NMA and DMA. Gibbs energy changes, enthalpies and entropies of micelle formation, respectively, have been determined by studying the variation of critical micelle concentration (c.m.c.) with temperature. Micelle formation in these solvents has been explained on the basis of several factors such as dielectric constant of the medium, its intermolecular H-bonding capability including solvophobic interaction.     

Ferric borate formation in aqueous solution

Potentiometric analyses indicate that previous investigations have overestimated the stability of ferric borate complexes. The FeB(OH) ₄ ²⁺ formation constant result obtained in the present work is_Bβ ₁ ^* = [FeB(OH) ₄ ²⁺ ][H⁺][Fe³⁺]^-1[B(OH)₃]^-1 = (5.4±0.3) x 10^-3 at 25.0°C and 0.7 molal ionic strength. Our result indicates that solution concentrations of FeOH²⁺ and FeB(OH) ₄ ²⁺ are approximately equal in aqueous solution for boric acid concentrations on the order of 0.3 molal. Fe(B(OH)₄) ₂ ⁺ is a minor species in solution compared to FeB(OH)₄ ²⁺ for conditions such that [B(OH)₃][H⁺]^-1≤ 350, and ferric borate complexation is insignificant in solutions such as seawater where [B(OH)₃] ≤ 4× 10^-4 molal.