Investigations of a series of nonionic surfactants of sugar-lipid hybrids by light scattering and electron microscopy

Sugar-lipid hybrids of the type C_nC_m were prepared by coupling an alkane chain (C_n) with a maltooligosaccharide (G_m) over an amide linkage. Coupling was performed with maltobionolactone (G₂) and n-alkylamine chains C_n withn=8,10,12,14,16, i.e. variation of the hydrophobic part of the molecule, and with hexadecylamine (C₁₆) and different maltooligosaccharides (G_m, m=2,3,4,6). The solution properties of the various products were studied by means of static and dynamic light scattering (LS) and by electron-microscopy (EM).The results may be summarized as follows: If the alkane chain is shorter thann=14, small spherical micelles with a radius of about 3 nm are observed. In time these micelles aggregate further to form increasingly larger spherical clusters which eventually precipitate. Long rod-like micelles form whenn 14. Contour length and chain stiffness were determined by applying theories of semiflexible chains. A qualitative confirmation of the light scattering results, i.e., micelle size and shape, was obtained from electron microscopy.     

The flexibility of rodlike micelles in aqueous solutions and the crossover concentrations among dilute,semidilute, and concentrated regimes

A flexibility parameter, the persistence length, has been evaluated from the radii of gyration and the contour lengths for rodlike micelles of heptaoxyethylene alkyl ethers (C _n E₇,n=12, 14, 16) and tetradecyldimethylammonium chloride (C₁₄DAC) and bromide (C₁₄DAB) at the observed crossover concentrations between dilute and semidilute regimes. The persistence length range is 43–73 nm, except for C₁₂E₇, for which it is 32 nm. The crossover concentrations between dilute and semidilute regimes for the semiflexible rodlike micelles calculated according to Ying and Chu as a function of the molecular weight, the contour length, and the persistence length are consistent with the observed values. The crossover concentration between semidilute and concentrated regimes was, on the other hand, calculated by using the same micelle parameters, including the value of thickness of cross-section of the rodlike micelles. The obtained values are at variance with the observed values. This means that rodlike micelles in semidilute and concentrated solutions might differ in size and/or flexibility from those in dilute solution.     

Kinetics of the dissociation of nonionic detergent micelles by a temperature-jump technique

The rate of dissociation of a nonionic detergent, octylphenyl polyoxyethylene ether, was studied by a temperature-jump technique. A relaxation process which is concentration-dependent was observed. A linear relation between the reciprocal relaxation time and the detergent concentration above the critical micelle concentration was obtained, from which the rate constant of dissociation k_n,n–1 of one molecule of detergent from the micelle has been determined. Values of k_n,n–1 equal to 0.4 ± 0.05 and 73 ± 5 sec^?1 at 24.8°C were obtained for detergents with 16 and 30 ethylene oxide units per molecule of surfactant, respectively, showing and increase of the rate constant of dissociation with the length of the hydrophilic-head chain.     

Effect of surfactant adsorption time on the observation of Newton black film in foam film

Observation of Newton black film (NBF) in foam film is possible only with a certain probability W which depends on the concentration C of surfactant in the solution and on the time t_a during which adsorption of surfactant at the solution/air interface has taken place. In the paper, the W(C,t_a) dependence is derived and used to analyze the effect of t_a on the critical surfactant concentration C_c below which NBF in foam film practically cannot be observed. An expression for the C_c(t_a) function is obtained which reveals that C_c decreases substantially with increasing t_a. This expression is found to describe well experimental C_c(t_a) data for foam films obtained from aqueous solution of the therapeutic surfactant INFASURF.     

Wormlike Micelle Formation and Rheological Behavior in the Aqueous Solutions of Mixed Sulfate Gemini Surfactant without Spacer Group and Dodecyltrimethylammonium Bromide

The rheological behavior of the aqueous solutions of mixed sulfate gemini surfactant with no spacer group, referred to as d‐C₁₂S, and dodecyltrimethylammonium bromide (C₁₂TABr) at a total concentration of 100 mmol·L⁻¹ but different molar ratios of C₁₂TABr to d‐C₁₂S (α₁) was investigated using steady rate and frequency sweep measurements. The wormlike micelles were formed over a narrow α₁ range of 0.20–0.27. The viscoelastic solutions exhibited Maxwell fluid behavior. At the optimum molar ratio of 0.25, the zero‐shear viscosity was as high as 600 Pa·s and the length of the mixed wormlike micelle was about 0.45–0.85 µm. The present result provides an example to construct long wormlike micelles by anionic gemini surfactant.     

The thermodynamics of micelles in surfactant solution: Lattice mean field theory

The lattice self-consistent mean field theory is applied to study the thermodynamics of micelles in surfactant solution. The model surfactants used are H ₄ T ₄ and H ₂ T ₄. The formation of spherical micelles is considered. The effect of the head length on the thermodynamic stability of the micellar solution is examined. The critical micelle concentration is studied at different lengths of head, fractional charge, solvent quality, and univalent salt concentration. A lower critical micelle concentration is associated with a larger aggregation number, while the smallest micelles are found at the lowest univalent salt concentration. The text was submitted by the authors in English.     

Determination of the Critical Micelle Concentration of Surfactant in Aqueous Solution by Twisted Intramolecular Charge Transfer Probe DMABN

With p-N,N-dimethylaminobenzonitrile (DMABN) as a probe, the variations of the intensity of its second fluorescence emission (I_a) and the corresponding characteristic wavelength (λ_a) with the surfactant concentration (c), here the examined surfactants (C₁₂TABr, SDS, C₁₂E₂₃, and C₁₂-3-C₁₂·2Br), were measured by Hitachi F4500 fluorescence spectrophotometer. The results showed that both the break points on the I_a–c curve and the minimum of the derivative variation corresponding to the λ_a–c curve agreed very well with the critical micelle concentration (cmc) of the surfactant in aqueous solution as measured by surface tension technique. Due to strong aggregation of C₁₂-3-C₁₂·2Br in aqueous solution, the information about loose micellar structure could be obtained by its λ_a–c curve.     

Mesoscopic simulation of alkylimidazoline self-aggregation in aqueous solution

A dissipative particle-dynamics method was used to simulate the self-aggregation behavior of 15 alkylimidazoline surfactants of different structures. The effects of concentration and structure of hydrophilic and lipophilic groups of the alkylimidazolines on the configuration and aggregation number (N_agg) of the micelles were also explored. Results show that the concentration of the alkylimidazoline has a significant influence on the configuration of the micelles generated. More specifically, alkylimidazolines of different concentrations are found to generate different structures (spherical, rod-shaped, layered, and interlaced) in aqueous solution. At low (1–10?wt%) and medium (40?wt%) concentrations, the micelles generated in aqueous solution are spherical and rod-shaped, respectively. At higher concentrations (80?wt%), the micelles generated present interlaced shapes with rod-shaped and layered micelles when the length of the lipophilic chain is greater than C₁₃ or the hydrophilic group is H_c. N_agg is strongly dependent on alkylimidazoline concentration and increases as concentration increases. N_agg is also greatly dependent on the structure of the hydrophilic and lipophilic groups present: it increases as the chain length of the lipophilic group increases but decreases as that of the hydrophilic group increases.     

Micelle structure in isotropic aqueous colloids of a poly(oxyethylene) amphiphile C12E8

Micelle structure in aqueous colloids in the isotropic liquid phase (L₁) of a nonionic amphipile (n-dodecyl octa(oxyethylene glycol) monoether (C₁₂E₈) has been investigated as a function of concentration and temperature using light scattering (LS), viscometry, NMR, and small-angle X-ray scattering (SAXS).The spherical micelles, having a radius of 28–31 Å, remain in a wide concentration range from very dilute to ca. 42 wt %. The micelle size increases sligthly with increasing temperature in the range of 25–60 °C. In the concentrated colloids, the spherical micelles are likely to be arranged in a certain ordered structure. Even at such a high concentration as 30 wt %, the isotropic colloid shows Newtonian flow. This suggests that interaction between micelles in the ordered structure is very weak and the structure is very fragile. Moreover, coexistence of the isotropic phase and the ordered structure in L₁ phase is discussed.     

单分散ZnS纳米球与纳米梭之间的形貌转换及光学性能研究

利用平平加作为表面活性剂, 正戊醇作为助表面活性剂, 环己烷作为油相, 以硫化钠(Na₂S)和醋酸锌(Zn(Ac)₂)作为反应物, 通过控制反应条件在反相胶束体系中合成出单分散的ZnS纳米球与纳米梭. 采用XRD和TEM对产物的结构和形貌进行表征, 结果表明产物均为六方相ZnS, 晶胞参数为a＝0.3823 nm, c＝56.2 nm, 纳米球直径约为50 nm, 纳米梭直径约为60 nm, 长度约为110 nm. 采用UV-Vis(紫外可见吸收光谱)和PL(荧光光谱)研究了产物的光学性能. 纳米球的紫外可见光谱的吸收峰出现在288 nm处, 而纳米梭在305 nm处有强吸收峰, 与块体材料相比, 分别有约60和50 nm的蓝移. 当激发波长为270 nm时, 纳米球和纳米梭产物分别能够发出波长为408和303 nm的紫外光.     

Conductive,Monodisperse Polyaniline Nanofibers of Controlled Length Using Well‐Defined Cylindrical Block Copolymer Micelles as Templates

Stable colloidal dispersions of polyaniline (PAni) nanofibers with controlled lengths from about 200 nm–1.1 μm and narrow length distributions (L_w/L_n<1.04; L_w=weight average micelle length, L_n=number average micelle length) were prepared through the template‐directed synthesis of PAni using monodisperse, solution‐self‐assembled, cylindrical, block copolymer micelles as nanoscale templates. These micelles were prepared through a crystallization‐driven living self‐assembly method from a poly(ferrocenyldimethylsilane)‐b‐poly(2‐vinylpyridine) block copolymer (PFS₂₅‐b‐P2VP₄₂₅). This material was initially self‐assembled in iPrOH to form cylindrical micelles with a crystalline PFS core and a P2VP corona and lengths of up to several micrometers. Sonication of this sample then yielded short cylinders with average lengths of 90 nm and a broad length distribution (L_w/L_n=1.32). Cylindrical micelles of PFS₂₅‐b‐P2VP₄₂₅ with controlled lengths and narrow length distributions (L_w/L_n<1.04) were subsequently prepared using thermal treatment at specific temperatures between 83.5 and 92.0 °C using a 1D self‐seeding process. These samples were then employed in the template‐directed synthesis of PAni nanofibers through a two‐step procedure, where the micellar template was initially stabilised by deposition of an oligoaniline coating followed by addition of a polymeric acid dopant, resulting in PAni nanofibers in the emeraldine salt (ES) state. The ES–PAni nanofibers were shown to be conductive by scanning conductance microscopy, whereas the precursor PFS₂₅‐b‐P2VP₄₂₅ micelle templates were found to be dielectric in character.     

Synthesis and pH-sensitive micellization of doubly hydrophilic poly(acrylic acid)-b-poly(ethylene oxide)-b-poly(acrylic acid) triblock copolymer in aqueous solutions

A doubly hydrophilic triblock copolymer poly(acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) with M _w/M _n = 1.15 was synthesized by atom transfer radical polymerization of t-butyl acrylate (tBA), followed by acidolysis of the PtBA blocks. The pH-sensitive micellization of PAA-b-PEO-b-PAA in acidic solution was investigated by potentiometric titration, fluorescence spectrum, dynamic light scattering and zeta potential. The pK _a was 6.6 and 6.0 in deionized water and in 0.1 mol/L NaCl solution, respectively. The copolymer formed micelles composed of a weakly hydrophobic core of complexed PAA and PEO and a hydrophilic PEO shell in 1 mg/mL solution at pH < 5.5 due to hydrogen bonding. The critical micelle concentration was 0.168 mg/mL at pH 2.0. At pH < 4.5, steady and narrow distributed micelles were formed. Increasing pH to 5.0, unsteady and broad distributed micelles were observed. At pH > 5.5, the micelle was destroyed owing to the ionization of the PAA blocks.     

<Superscript>13</Superscript>C NMR investigation of the structure of alkylammonium chloride micells in aqueous solutions

¹³C NMR chemical shifts are obtained for aqueous solutions of alkylammonium chlorides (C₆–C₉) in the region of the critical micelle concentration (CMC). A new method of processing ¹³C NMR experimental data for aqueous solutions of alkylammonium chlorides is developed to calculate the aggregation numbers N of micelles and the equilibrium constants K of the micelle formation within the law of mass action. With the use of these N and K values the standard Gibbs energy of the micelle formation and its increment of −1.8 kJ/mol are found for the methylene group. A small increment confirms the hypothesis about the structure of micelles consisting of both contact and hydrated associates. The structural model of the association of alkylammonium chlorides in water, the effect of alkyl chain length on the CMC, the hydrophobic interaction, the formation of hydrate associates, and also a possible classification of surfactants based on this are discussed.     

Properties of two polymerizable surfactants aqueous solutions: dodecylethylmethacrylatedimethylammonium bromide and hexadecylethylmethacrylatedimethylammonium bromide. I. Critical micelle concentration

The aggregation of two polymerisable surfactants dodecylethylmethacrylatedimethylammonium bromide (C₁₂PS) and hexadecylethylmethacrylatedimethylammonium bromide (C₁₆PS) was studied with a battery of methods. Both surfactants form premicelles at low concentration, and show a critical micelle concentration and a transition between spherical and rod-like micelles. The micelle ionization degree and the adsorption at the air/solution interface were also studied. Results are interpreted on the basis of the conformation of the polar head group.     

Growth of Gemini Surfactant Micelles Under the Influence of Additives: DLS Studies

Results are presented on the first extensive study on the influence of additives on the growth of gemini; alkanediyl α, ω - bis(dimethylcetylammonium bromide) surfactant micelles (16-s-16, with s = 5, 6); as measured by dynamic light scattering technique at 30°C. The effect of adding n-butanol, n-pentanol, n-hexanol, and n-hexylamine in the absence or presence of general ionic salt potassium bromide on 0.03 M gemini solutions were observed. The tendency for micelles to grow from spherical to rodlike structures is decisively influenced by the spacer length s. At 30°C, the micellar growth was more for s being 5, which has been interpreted in terms of short spacer having strong propensity for micellar growth. Addition of KBr plays a role in screening of the electrostatic interactions, thus promoting a change of morphology of the aggregates and giving rise to high hydrodynamic diameter (D _h ) values. The micellar growth in presence of alcohols is interpreted in terms of the formation of the gemini–alcohol mixed micelles which followed the pattern C₆OH>C₅OH>C₄OH. For equal chain length additives C₆OH and C₆NH₂, the growth was more pronounced in case of alcohol. Also, in case of C₆NH₂, the value of D _h reached to almost constancy or decreased to some extent, which is discussed in terms of its partitioning in aqueous phase. A combined presence of KBr and n-alcohols or n-hexylamine produced favorable conditions for micellar growth due to synergistic effect.     

Rheological behavior of PAA–C n TAB complex: influence of PAA charge density and surfactant tail length in PAA semidilute aqueous solution

Interactions between anionic polyelectrolyte, poly(acrylic acid) (PAA), and cationic surfactant, alkyltrimethylammonium bromide (C _n TAB), were investigated by rheological measurements in semidilute PAA solution. The dependences of the rheological behavior on the chain length of the surfactant, PAA neutralization degree, and temperature were discussed. The results revealed that both dodecyl and cetyltrimethylammonium bromides (C₁₂TAB and C₁₆TAB) could increase the viscosity of PAA solution when the surfactant amounts surpassed a critical surfactant concentration (C _c), and C _c of C₁₆TAB was lower than that of C₁₂TAB at same PAA neutralization degree. The increase of viscosity is attributed to the surfactant micelles bridging of the polymer chains and confine the mobility PAA chain. On the other hand, it is found that the hydrogen bonding also played an important role in the PAA–C _n TAB system, especially in lower neutralization degree PAA solution, which results in the viscosity increase rapidly with the added surfactant into lower neutralization degree PAA solution.     

The synthesis and self‐assembly of ABA amphiphilic block copolymers containing styrene and oligo(ethylene glycol) methyl ether methacrylate in dilute aqueous solutions: Elevated cloud point temperatures for thermoresponsive micelles

A series of ABA amphiphilic triblock copolymers possessing polystyrene (PS) central hydrophobic blocks, one group with “short” PS blocks (DP = 54–86) and one with “long” PS blocks (DP = 183–204) were synthesized by atom transfer radical polymerization. The outer hydrophilic blocks were various lengths of poly(oligoethylene glycol methyl ether) methacrylate, a comb‐like polymer. The critical aggregation concentrations were recorded for certain block copolymer samples and were found to be in the range circa 10⁻⁹ mol L⁻¹ for short PS blocks and circa 10⁻¹² mol L⁻¹ for long PS blocks. Dilute aqueous solutions were analyzed by transmission electron microscopy (TEM) and demonstrated that the short PS block copolymers formed spherical micelles and the long PS block copolymers formed predominantly spherical micelles with smaller proportions of cylindrical and Y‐branched cylindrical micelles. Dynamic light scattering analysis results agreed with the TEM observations demonstrating variations in micelle size with PS and POEGMA chain length: the hydrodynamic diameters (D_H) of the shorter PS block copolymer micelles increased with increasing POEGMA block lengths while maintaining similar PS micellar core diameters (D_C); in contrast the values of D_H and D_C for the longer PS block copolymer micelles decreased. Surface‐pressure isotherms were recorded for two of the samples and these indicated close packing of a short PS block copolymer at the air–water interface. The aggregate solutions were demonstrated to be stable over a 38‐day period with no change in aggregate size or noticeable precipitation. The cloud point temperatures of certain block copolymer aggregate solutions were measured and found to be in the range 76–93 °C; significantly these were ∼11 °C higher in temperature than those of POEGMA homopolymer samples with similar chain lengths. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7739–7756, 2008     

Acid soap formation of oleic acid and catanionic complex formation in the alkyldimethylamine oxide/sodium oleate equimolar mixtures

The influence of adding alkyldimethylamine oxide (CnDMAO) with varying alkyl chain lengths (n_c) on the acid soap formation of oleic acid was investigated. The solutions of equimolar mixtures of CnDMAO and sodium oleate (Na⁺Ol^–), each 25 mmol kg^–1, became turbid at a certain critical pH (pH_c) on decreasing pH. Values of the pH_c depended on n_c and showed the minimum at C10DMAO/NaOl mixture. The presence of the minimum was interpreted in terms of two different kinds of the complex formed in the micelles depending on n_c: the catanionic complex (CnDMAOH⁺/Ol^–) in the mixed micelles of n_c=16, 14, 12 and 10, and the acid soap of oleic acid for C6DMAO/NaOl and C8DMAO/NaOl mixtures. At pH_c where the amounts of these complexes of double-chain nature reached certain critical values in the mixed micelles, a phase separation (most probably lamella formation) took place. It was expected that the critical amount of the catanionic complex was smaller for the mixtures of higher n_c values and hence pH_c increased with n_c for the mixtures n_c10. For the mixtures of n_c<10, it was expected that the amount of the acid soap in the mixed micelles increased with decreasing n_c at a given pH and the pH_c increased with decreasing n_c. Micelle compositions at cmc were evaluated on the basis of the regular solution theory coupled with the pseudo phase approximation. The micelle compositions at 100 mmol kg^–1 were examined with ¹³C-NMR. The results showed the mixed micelle formation for n_c=16–10, while the micelles mostly consisting of oleic acid for the mixtures of n_c=8 and 6. The assumption of two different complexes for the two groups of the mixture was thus supported. The cmc range of mixed micelles was evaluated and it was well correlated with the observed concentration range of pyrene fluorescence change.     

Diffusion Coefficients and Structure Properties in the Pluronic F127/n‐C4H9OH/H2O System

Abstract

Diffusion coefficients of different aggregates in aqueous solutions formed by an amphiphilic block copolymer, Pluronic F127 (F127), were determined by cyclic voltammetry, and the critical micelle concentration (CMC, 4.31 × 10^?4 mol L^?1) of F127 was obtained. The added n‐butanol facilitates the formation of micelles from the monomers of F127 and makes the critical micelle temperature (CMT) of F127 solutions decrease. The diffusion coefficient of the F127 micelles decreases relatively fast at first with increasing n‐butanol and then the decreasing trend slows after the solubilization of n‐butanol in micelles reaches maximum.