Wormlike aggregates from a supramolecular coordination polymer and a diblock copolymer

The formation of wormlike micelles in mixed systems of a supramolecular coordination polymer Zn-L2EO4 and a diblock copolymer P2MVP41-b-PEO205 is investigated by light scattering and Cryo-TEM. By direct mixing at a stoichiometric charge ratio, the above mixtures proved to be capable of formation of spherical micelles with a radius of about 25 nm (Yan et al. Angew. Chem., Int. Ed.; 2007, 46, 1807-1809). Lately, we find wormlike micelles with a hydrodynamic radius >150 nm in a mixture with excess positive charge, that is, a negative charge fraction f- < 0.5. The transformation between wormlike and spherical micelles can be realized by variation of the mixing ratio through different protocols. Upon addition of negatively charged Zn-L2EO4 to a mixture with excess positively charged P2MVP41-b-PEO205, most of the wormlike micelles are transformed into spherical ones; upon addition of positively charged P2MVP41-b-PEO205 to a mixture of pure spherical micelles, wormlike micelles can be produced again. The effect of sample preparation protocol, sample history, and concentration on this transformation process is systematically reported in this article. A possible mechanism for the formation of wormlike micelles is proposed.     

Effect of alkali halide salt additives on the structure of poly(vinyl alcohol) films cast from aqueous solutions

The molecular structures of poly(vinyl alcohol) films cast from polymer aqueous solutions (1 mol/L) containing 0.1 mol/L of LiCl, NaF, NaCl, KCl, CsCl, KBr, and KI salts are studied via FTIR spectroscopy. The addition of any of these salts except LiCl leads to an increase in the degree of crystallinity of poly(vinyl alcohol) in a film by a factor of 1.3–1.6. In contrast, LiCl significantly decreases the crystallinity of the polymer. It is found that, in the IR spectra of the films containing salt additives, the position of the maximum in the band of the stretching vibrations of OH groups of the polymer is shifted relative to its position in the IR spectra of the films free of salt additives. The magnitude and direction of this band shift depend on the types (anion or cation) and radii of ions comprising salts. The observed effects are interpreted in terms of existing ideas on the interactions of salt ions with the OH groups of water and other hydroxyl-containing molecules.     

Room temperature sphere-to-rod growth and gelation of PEO-PPO-PEO triblock copolymers in aqueous salt solutions

The effects of NaCl and KF on the sphere-to-rod micellar growth behavior of triblock copolymers having two different compositions, (EO)20(PO)70(EO)20 (P123) and (EO)26(PO)40(EO)26 (P85), have been studied by dynamic light scattering (DLS), small angle neutron scattering (SANS) and dilute solution viscometry. NaCl can effectively tune the sphere-to-rod growth temperature of the micelles of both these copolymers and induce micellar growth down to the room temperature and below. The growth behavior is found to be dependent on the composition of the copolymer as P123 being more hydrophobic shows the room temperature growth in the presence of ethanol at significantly lesser NaCl concentration than the less hydrophobic copolymer P85. DLS studies depict for the first time the growth driven transition of the copolymer solutions from dilute to semi-dilute regime as a function of copolymer and salt concentrations. KF can also induce room temperature growth of the P123 micelles at lesser salt concentration than NaCl but it fails to induce any such growth of the P85 micelles. A pseudo-binary temperature-concentration phase diagram on 15% copolymer solutions shows the variation of the sphere-to-rod transition temperature and the cloud point of the copolymer solutions as a function of salt concentration.     

Aqueous biphasic systems formed by nonionic polymers I. Effects of inorganic salts on phase separation

The effect of salts KSCN, KI, KBr, KCl, KClO₄, KF, K₂SO₄ and NH₄Cl, LiCl, NaCl, KCl, CsCl on the binodials of the phase diagrams for aqueous biphasic dextranpolyvinylpyrrolidone, dextran-polyvinyl alcohol, dextran-ficoll and dextran-polyethylene glycol systems was studied. It is established that the K-salts present at the concentrations of 0.1 and 0.5 mol/kg alter the binodials of the phase diagrams for the above systems. The effect of a salt is found to be related to the lyotropy of the salt quantified by the salt molal surface tension increment. It is assumed that phase separation in an aqueous polymer biphasic system is affected by the presence of a salt mainly due to the effect of the salt on the structure and/or state of water in the system.     

Wormlike morphology formation and stabilization of "pluronic p123" micelles by solubilization of pentaerythritol tetraacrylate

A transition from spherical to wormlike micelles of a poly(ethylene oxide) 20- block-poly(propylene oxide) 70- block-poly(ethylene oxide) 20 triblock copolymer Pluronic P123 induced by solubilization of a tetrafuctional monomer, Pentaerythritol tetraacrylate (PETA), in aqueous media has been studied. The wormlike micelles shape was locked by UV cross-linking of PETA within the micelles resulting in stabilized polymeric micelles (SPMs). The stability of SPMs in a good solvent for both polyether blocks like THF, and upon dilution below the critical micelle concentration (CMC) of P123 in water was confirmed by dynamic light scattering (DLS) and scanning force microscopy (SFM). Formation of cadmium sulfide (CdS) nanoparticles within the wormlike SPMs was carried out via the reduction of Cd (2+) with NaS and analyzed by transmission electron microscopy (TEM) and UV-vis absorption measurements. A stable water-dispersible hybrid system consisting of CdS quantum dots embedded into the wormlike SPMs was obtained.     

Improved micellar hydration and gelation characteristics of PEO-PPO-PEO triblock copolymer solutions in the presence of LiCl

LiCl-induced changes in the micellar hydration and gelation characteristics of aqueous solutions of the two triblock copolymers F127 (EO(100)PO(70)EO(100)) and P123 (EO(20)PO(70)EO(20)) (where EO represents the ethylene oxide block and PO represents the propylene oxide block) have been studied by small-angle neutron scattering (SANS) and viscometry. The effect of LiCl was found to be significantly different from those observed for other alkali metal chloride salts such as NaCl and KCl. This can be explained on the basis of the complexation of hydrated Li(+) ions with the PEO chains in the micellar corona region. The interaction between the chains and the ions is more significant in the case F127 because of its larger PEO block size, and therefore, micelles of this copolymer show an enhanced degree of hydration in the presence of LiCl. The presence of the hydrated Li(+) ions in the micellar corona increases the amount of mechanically trapped water there and compensates more than the water molecules lost through the dehydration of the PEO chains in the presence of the Cl(-) ions. The enhancement in micellar hydration leads to a decrease in the minimum concentration required for the F127 solution to form a room-temperature cubic gel phase from 18% to 14%. Moreover, for both copolymers, the temperature range of stability of the cubic gel phase also increases with increasing LiCl concentration, presumably because of the ability of the Li(+) ions to reduce micellar dehydration with increasing temperature. Viscosity studies on a poly(ethylene glycol) (PEG) homopolymer with a size equivalent to that of the PEO block in F127 (4000 g/mol) also suggest that the dehydrating effect of the Cl(-) ion on the PEG chain is compensated by its interaction with the hydrated Li(+) ions.     

Effect of inorganic salts on the micellar behaviour of ethylene oxide-propylene oxide block copolymers in aqueous solution

The aggregation behaviour of two ethylene oxide-propylene oxide block copolymers (PEO-PPO-PEO) in aqueous solution has been investigated in the presence of added salts (KCNS, KI, KBr, KCl and KF) by viscosity, cloud point, light scattering, pulse gradient spin echo NMR, and solubilization measurements. The salts have a strong effect on the cloud points of the pluronics. Both P-85 and L-64 form micelles which increase in size and change into elongated shapes when the cloud point is approached. The changes of size and shape of the micelles, revealed by the intrinsic viscosity and rheological properties, seem to occur at the same temperature relative to the cloud point, independent of the nature of the salt. The onset of micelle formation is also shifted in the same direction as the cloud point by the salts, but by a much smaller amount.     

Spontaneous generation of amphiphilic block copolymer micelles with multiple morphologies through interfacial Instabilities

We introduce a method for the formation of block copolymer micelles through interfacial instabilities of emulsion droplets. Amphiphilic polystyrene-block-poly(ethylene oxide) (PS-PEO) copolymers are first dissolved in chloroform; this solution is then emulsified in water and chloroform is extracted by evaporation. As the droplets shrink, the organic solvent/water interface becomes unstable, spontaneously generating a new interface and leading to dispersion of the copolymer as micellar aggregates in the aqueous phase. Depending on the composition of the copolymer, spherical or cylindrical micelles are formed, and the method is shown to be general to polymers with several different hydrophobic blocks: poly(1,4-butadiene), poly(-caprolactone), and poly(methyl methacrylate). Using this method, hydrophobic species dissolved or suspended in the organic phase along with the amphiphilic copolymer can be incorporated into the resulting micelles. For example, addition of PS homopolymer, or a PS-PEO copolymer of different composition and molecular weight, allows the diameter and morphology of wormlike micelles to be tuned, while addition of hydrophobically coated iron oxide nanoparticles enables the preparation of magnetically loaded spherical and wormlike micelles.     

Sodium chloride and ethanol induced sphere to rod transition of triblock copolymer micelles

Dynamic light scattering (DLS), small-angle neutron scattering (SANS), and viscosity studies have been carried out to examine the influence of NaCl and ethanol on the structure of triblock copolymer [(EO)20(PO)70(EO)20] (EO = ethylene oxide; PO = propylene oxide) micelles in aqueous medium. The studies show that while the pure triblock copolymer solutions do not show any significant growth of the micelles on approaching the cloud point, the presence of a small amount of ethanol (5-10%) induces a sphere to rod shape transition of micelles at high temperatures. Interestingly, this ethanol induced sphere to rod transition of micelles can be brought down to room temperature (25 degrees C) with the addition of NaCl. It is also found that NaCl alone cannot induce such sphere to rod transitions and excess ethanol suppresses them by increasing their transition temperature.     

Mixed micelles of a PEO-PPO-PEO triblock copolymer (P123) and a nonionic surfactant (C12EO6) in water. a dynamic and static light scattering study

The present article reports on static and dynamic light scattering (SLS and DLS) studies of aqueous solutions of the nonionic surfactant C12EO6 and the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO20PO68EO20 (P123) at temperatures between 25 and 45 degrees C. In water, P123 self-assembles into spherical micelles with a hydrodynamic radius of 10 nm, and at 40 degrees C, these micelles consist of 131 unimers. Addition of C12EO6 leads to an association of the surfactant molecules to the P123 micelles and mixed micelles are formed. The size and structure of the mixed micelles as well as interparticle interactions were studied by varying the surfactant-to-copolymer (C12EO6/P123) molar ratio. The novelty of this study consists of a composition-induced structural change of the mixed micelles at constant temperature. They gradually change from being spherical to polymer-like with increasing C12EO6 content. At low C12EO6/P123 molar ratios (below 12), the SLS measurements showed that the molar mass of the mixed micelles decreases with an increasing amount of C12EO6 in the micelles for all investigated temperatures. In this regime, the mixed micelles are spherical and the DLS measurements revealed a decrease in the hydrodynamic radius of the mixed micelles. An exception was found for C12EO6/P123 molar ratios between 2 and 3, where the mixed micelles become rodlike at 40 degrees C. This was the subject of a previous study and has hence not been investigated here. At high molar ratios (48 and above), the polymer-like micelles present a concentration-induced growth, similar to that observed in the pure C12EO6/water system.     

CO2 responsive wormlike micelles based on sodium oleate,potassium chloride and N,N-dimethylethanolamine

The anionic surfactant sodium oleate (NaOA) can self-assemble in aqueous solution in the presence of counter-ion inorganic salts to form wormlike micelles (WLMs), which exhibited viscoelastic behavior. In this paper, KCl was used to induce the formation of wormlike micelles with sodium oleate. In this process, we found that the addition of N, N-dimethylethanolamine (DMEA) can destroy the structure of WLMs leading significant decrease of viscosity. However, after introducing CO₂ into the ternary solution (KCl-NaOA-DMEA), the WLMs can be regenerated due to the electrostatic interaction between the protonated DMEA and the anionic surfactants. The addition of sodium hydroxide (NaOH) causes the electrostatic interaction between OA^- and DMEAH⁺ be destroyed, which results in the wormlike micelles becoming spherical micelles of lower viscosity. The transition of WLMs with high viscosity and low viscosity spherical micelles can be repeated several times by using CO₂ and NaOH.     

Selective salt transport through a crosslinked poly(L-glutamic acid) membrane for KCl/LiCl mixed systems

Selective salt transport of KCl over LiCl has been studied for a crosslinked poly(L -glutamic acid) membrane immersed in 80 vol.-% ethanol. The permeabilities (P_s) and solubilities were measured for various mixing ratios of the salts. The highest permselectivity (P_s (KCl)/P_s (LiCl) = 4,3) has been obtained at a LiCl mole fraction of 0,2. It is similar to that obtained in single salt systems.     

Phase behavior of a mixture of poly(isoprene)-poly(oxyethylene) diblock copolymer and poly(oxyethylene) surfactant in water

The phase behavior of a mixture of poly(isoprene)-poly(oxyethylene) diblock copolymer (PI-PEO or C250EO70) and poly(oxyethylene) surfactant (C12EO3, C12EO5, C12EO6, C12EO7, and C12EO9) in water was investigated by phase study, small-angle X-ray scattering, and dynamic light scattering (DLS). The copolymer is not soluble in surfactant micellar cubic (I1), hexagonal (H1), and lamellar (Lalpha) liquid crystals, whereas an isotropic copolymer fluid phase coexists with these liquid crystals. Although the PI-PEO is relatively lipophilic, it increases the cloud temperatures of C12EO3-9 aqueous solutions at a relatively high PI-PEO content in the mixture. Most probably, in the copolymer-rich region, PI-PEO and C12EOn form a spherical composite micelle in which surfactant molecules are located at the interface and the PI chains form an oil pool inside. In the C12EO5/ and C12EO6/PI-PEO systems, one kind of micelles is produced in the wide range of mixing fraction, although macroscopic phase separation was observed within a few days after the sample preparation. On the other hand, small surfactant micelles coexist with copolymer giant micelles in C12EO7/ and C12EO9/PI-PEO aqueous solutions in the surfactant-rich region. The micellar shape and size are calculated using simple geometrical relations and compared with DLS data. Consequently, a large PI-PEO molecule is not soluble in surfactant bilayers (Lalpha phase), infinitely long rod micelles (H1 phase), and spherical micelles (I1 phase or hydrophilic spherical micelles) as a result of the packing constraint of the large PI chain. However, the copolymer is soluble in surfactant rod micelles (C12EO5 and C12EO6) because a rod-sphere transition of the surfactant micelles takes place and the long PI chains are incorporated inside the large spherical micelles.     

A calorimetry and light scattering study of the formation and shape transition of mixed micelles of EO20PO68EO20 triblock copolymer (P123) and nonionic surfactant (C12EO6)

The interaction between the nonionic surfactant C12EO6 and the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO20PO68EO20 (P123) has been investigated by means of isothermal titration and differential scanning calorimetry (DSC) as well as static and dynamic light scattering (SLS and DLS). P123 self-assembles in water into spherical micelles at ambient temperatures. At raised temperatures, the DSC data revealed a sphere-to-rod transition of the P123 micelles around 60 degrees C. C12EO6 interacts strongly with P123 micelles in aqueous solution to give mixed micelles with a critical micelle concentration (cmc) well below the cmc for pure C12EO6. The presence of C12EO6 also lowers the critical micelle temperature of P123 so aggregation starts at significantly lower temperatures. A new phenomenon was observed in the P123-C12EO6 system, namely, a well-defined sphere-to-rod transition of the mixed micelles. A visual phase study of mixtures containing 1.00 wt % P123 showed that in a narrow concentration range of C12EO6 both the sphere-to-rod transition and the liquid-liquid phase separation temperature are strongly depressed compared to the pure P123-water system. The hydrodynamic radius of spherical mixed micelles at a C12EO6/P123 molar ratio of 2.2 was estimated from DLS to be 9.1 nm, whereas it is 24.1 nm for the rodlike micelles. Furthermore, the hydrodynamic length of the rods at a molar ratio of 2.2 is in the range of 100 nm. The retarded kinetics of the shape transition was detected in titration calorimetric experiments at 40 degrees C and further studied by using time-resolved DLS and SLS. The rate of growth, which was slow (>2000 s), was found to increase with the total concentration.     

Wormlike micelles mediated by polyelectrolyte

Aqueous solutions of the anionic surfactant potassium oleate (K-oleate) were studied using small-angle neutron scattering (SANS), steady-state rheology, and cryogenic transmission electron microscopy (cryo-TEM). The micellar structural changes induced by the addition of potassium chloride (KCl) and sodium polystyrenesulfonate (PSS) of different molecular weights were investigated. Upon addition of KCl, a transition from spherical to wormlike micelles was detected from the SANS data and confirmed by the cryo-TEM pictures. The rheological measurements revealed a strong dependence of the low-shear viscosity on the concentration of salt: a broad maximum in the viscosity curve was observed upon addition of KCl, characteristic of the growth of micelles into long worms, followed by branching. The addition of PSS to salt-free solutions of K-oleate had a significant effect on the scattering patterns, revealing partial growth of the spherical micelles into rodlike micelles. In contrast, in the presence of high salt concentrations, addition of PSS to solutions of wormlike micelles did not bring any noticeable modifications in the scattering. However, in the same salt conditions, a clear effect was observed on the low shear viscosity upon addition of PSS, which was found to depend significantly on molecular weight. This suggests a novel way of impacting the viscosity of solutions of wormlike micelles.     

Viscoelastic micellar solutions in a mixed nonionic fluorinated surfactants system and the effect of oils

Formation and rheological behavior of viscoelastic wormlike micelles in aqueous solution of a mixed system of nonionic fluorinated surfactants, perfluoroalkyl sulfonamide ethoxylate, C8F17SO2N(C3H7)(CH2CH2O)nH (abbreviated as C8F17EOn) was studied. In the water-surfactant binary system C8F17EO20 forms an isotropic micellar solution over wide concentration range (>85 wt %) at 25 degrees C. With successive addition of C8F17EO1 to the aqueous C8F17EO20 solution, viscosity of the solution increases swiftly, and a viscoelastic solution is formed. The oscillatory rheological behavior of the viscoelastic solution can be described by Maxwell model at low-frequency region, which is typical of wormlike micelles. With further addition of C8F17EO1, the viscosity decreases after a maximum and phase separation occurs. Addition of a small amount of fluorinated oils to the wormlike micellar solution disrupts the network structure and decreases the viscosity sharply. It is found that polymeric oil, PFP (F-(C3F6O)nCF2CF2COOH), decreases the viscosity more effectively than the perfluorodecalin (PFD). The difference in the effect of oil on rheological properties is explained in terms of the solubilization site of the oils in the hydrophobic interior of the cylindrical aggregates, and their ability to induce rod-sphere transition.     

Differential scanning calorimetry and large deformation behaviour of kappa-carrageenan gels containing alkali metal ions

Differential scanning calorimetry and extension tests were carried out on kappa-carrageenan gels in the presence of the alkali metal salts LiCl, NaCl, KCl and CsCl. The endothermic peak accompanying the melting of gels shifted to higher temperatures with increasing concentrations of alkali metal salt. The breaking force of gels increased with increasing concentrations of added KCl and CsCl, and decreased with increasing concentrations of added NaCl. The breaking force of the gel containing LiCl decreased with the first level of addition, then increased slightly with two further additions and finally decreased again at the highest level of addition.     

Phase behavior and microstructures of nonionic fluorocarbon surfactant in aqueous systems

The phase behavior and self-assembled structures of perfluoroalkyl sulfonamide ethoxylate, C8F17SO2N(C3H7)(CH2CH2O)20H (abbreviated as C8F 17EO20), a nonionic fluorocarbon surfactant in an aqueous system, has been investigated by the small-angle X-ray scattering (SAXS) technique. The C8F17EO20 forms micelles and different liquid crystal phases depending on the temperature and composition. The fluorocarbon micellar structure induced by temperature or composition change and added fluorocarbon cosurfactant has been systematically studied. The SAXS data were analyzed by the indirect Fourier transformation (IFT) and the generalized indirect Fourier transformation (GIFT) depending on the volume fraction of the surfactant and complemented by plausible model calculations. The C8F17EO20 forms spherical type micelles above critical micelle concentration (cmc) in the dilute region. The micelle tends to grow with temperature; however, the growth is not significant on changing temperature from 15-75 degrees C, which is attributed to the higher clouding temperature of the surfactant (>100 degrees C). On the other hand, the micellar structure (shape and size) is apparently unaffected by composition (1-25 wt %) at 25 degrees C. Nevertheless, addition of fluorocarbon cosurfactant of structure C8F17SO2N(C3H7)(CH2CH2O)H (abbreviated as C8F17EO1) to the semidilute solution of C8F17EO20 (25 wt %) favors micellar growth, which finally leads to the formation of viscoelastic wormlike micelles, as confirmed by rheometry and supported by SAXS. The onset sphere-to-wormlike transition in the structure of micelles in the C8F17EO20/water/C8F17EO1 system is due to the fact that the C8F17EO1 tends to go to the surfactant palisade layer so that the critical packing parameter increases due to a decrease in the effective cross-sectional area of the headgroup. As a result, spherical micelles grow into a cylinder, which after a certain concentration entangle to form a rigid network structure of wormlike micelles.     

苯基桥键型介孔材料的制备与表征

以1,4-二(三乙氧基硅基)-苯为硅源,聚氧乙烯-聚氧丙烯-聚氧乙烯三嵌段共聚物为模板剂,十六烷基三甲基溴化铵为共模板剂,乙醇为共溶剂,在酸性条件下合成了球形的苯基桥键型有序介孔材料。X射线衍射和透射电镜表征结果表明,该材料具有有序的二维六方相介观结构;傅立叶红外变换、13C和29S i固体核磁共振表征证实硅胶骨架中成功引入了苯基桥键,且在合成和模板移除过程中未发生S i—C键断裂;元素分析表明材料含碳量为34%~39%;热重分析说明材料稳定温度可达300℃;氮气吸附脱附揭示了材料有较高的比表面积(500~600 m2/g)和窄的孔径分布(3.21~3.95 nm)。将该苯基材料不经化学改性直接用作反相高效液相色谱固定相,并与商品键合硅胶苯基色谱柱比较,发现桥键型苯基材料对芳香类化合物具有很好的分离选择性,残留硅羟基明显减少,作为一种新的液相色谱填料具有很好的应用前景。     

The determination of the complex refractive indices of some concentrated aqueous salt solutions at submillimetre wavelengths

Recent developments in far infrared laser spectrometry and dispersive Fourier transform spectrometry have allowed the full spectral variation of both parts of the complex refractive indices of some aqueous salt solutions in the spectral region 25–450 cm^?1 to be determined. The salts studied were LiCl, LiClO₄, NaCl, NaClO₄, NaI, KCl, KBr, KI, KF, MgCl₂, Mg(ClO₄) and Bu₄NBr (tetrabutylammonium bromide). The results show that in the presence of some electrolytes the optical constants of the solution differ significantly from those of pure water, and that in localised spectral regions the absorption can be many times less than that of pure water.