Polymer-directed synthesis of penniform BaWO4 nanostructures in reverse micelles

Novel penniform superstructures of BaWO4 nanowires have been successfully synthesized in catanionic reverse micelles by using a double-hydrophilic block copolymer as the directing agent. This synthetic method is very simple, mild, and controllable, and it provides a novel method for direct solution-growth of hierarchical nanostructures based on inorganic nanowires.     

Synthesis of single crystal BaWO4 nanowires in catanionic reverse micelles

High aspect-ratio, single crystal BaWO4 nanowires with diameters as small as 3.5 nm and lengths up to more than 50 microns were synthesized in catanionic reverse micelles formed by an equimolar mixture of two surfactants: undecylic acid and decylamine.     

Growth of BaWO4 fishbone-like nanostructures in w/o microemulsion

BaWO(4) fishbone-like nanostructures with fourfold structural symmetry have been successfully grown in w/o microemulsion. The BaWO(4) fishbone-like nanostructures have four rows of nanorods, epitaxially grown on the stem and perpendicular to the stem. The obtained samples are characterized by means of XRD, TEM, HRTEM, and SEM. It is found that the water content has a large influence on the size of the product and the molar ratio between cations and anions plays an important role in the morphology of the product. It is assumed that site-selective surfactant adsorption may be responsible for the formation of the BaWO(4) fishbone-like nanostructures.     

Electrostastic control of spontaneous curvature in catanionic reverse micelles

By means of small-angle neutron scattering and conductivity measurements, we study the microstructure of octylammoniumoctanoate/octane/water catanionic reverse microemulsions with an excess of anionic or cationic surfactant. Increasing the surface charge makes the microemulsion able to incorporate much more water than in the neutral case, up to 10 water molecules per surfactant. Even with charges in the surfactant film, wormlike micelles are present in the microemulsion domain. Along water dilution lines, the classical rod-to-sphere transition due to the minimization of the curvature energy of the rigid surfactant film is observed. When temperature is decreased, a re-entrant phase transition associated with the liquid-gas equilibrium of attractive cylinders is observed. Using the framework of the Tlusty-Safran theory, attraction could originate from junctions between wormlike reverse micelles. In any case, the spontaneous curvature of the catanionic surfactant film depends on both the temperature and the net charge, whatever the sign of the latter.     

Phase behavior, topology, and growth of neutral catanionic reverse micelles

The ternary catanionic system octylammoniumoctanoate/octane/water is studied by combined SANS, light scattering, conductivity, and phase diagram approach in the water-poor microemulsion region. The sphere-to-cylinder growth and branching depends on the concentration, the water-to-surfactant ratio, and the temperature. The unidimensional growth leads to a network of interconnected wormlike micelles. Like most studied linear nonionic surfactants, in this true catanionic system at equimolarity of anionic and cationic surfactant, the curvature toward water increases with temperature, making connections between cylinders less frequent.     

Synthesis and characterization of ultrafine CeF3 nanoparticles modified by catanionic surfactant via a reverse micelles route

In this article, we firstly reported on the synthesis and characterization of ultrafine CeF3 nanoparticles (NPs) modified by catanionic surfactant via a reverse micelles-based route. The catanionic surfactant PN was prepared by mixing the di(2-ethylhexyl) phosphoric acid (DEHPA) and primary amine (N1923) with 1:1 molar ratio. It exhibited a high surface activity and formed much small reverse micelles in comparison with its individual component (DEHPA or N1923). The PN reverse micelles were then used as templates to prepare ultrafine CeF3 NPs. The narrow distributed nanoparticles have an average diameter 1.8 nm. FTIR spectra indicated that there existed strong chemical interactions between nanoparticles and the adsorbed surfactants. The modification resulted in the FTIR peak position of PO shifting to lower energy. Due to the effect of modification and small size, the CeF3 NPs showed a remarkable red shift of 54 nm in the fluorescence emission in comparison with that of bulk material and a red shift of 18 nm in contrast with that of the normal CeF3 NPs with an average diameter of 16 nm.     

Horseradish peroxidase activity in a reverse catanionic microemulsion

In this paper we present the first results of enzymatic activities in a reverse microemulsion medium based on a mixture of an anionic and a cationic surfactant, called catanionic microemulsion. The studied system is composed of sodium dodecyl sulfate (SDS)/dodecyltrimethylammonium bromide (DTAB)/n-hexanol/citrate buffer/n-dodecane, with high SDS/(SDS + DTAB) weight fractions. It turns out that the results are similar to those obtained in classical reverse microemulsions, except that the presence of DTAB exerts an inhibiting effect on the enzyme. Nevertheless, enzymatic superactivities are found even at a DTAB to total surfactant ratio of 15%, corresponding to 3% weight fraction of cationic surfactant in the microemulsion. The influence of pH and hexanol content on the enzymatic activities is also studied.     

Spontaneous evolution of nanostructures by light-driven growth of micelles obtained from in situ nanoparticlization of conjugated polymers

To simplify processes to produce self-assembled nanostructures from polymeric materials, there have been several attempts for in situ self-assembly of block copolymers. As one of these strategies, we developed the in situ nanoparticlization of conjugated polymers (INCP) process to construct various stable nanostructures without postsynthetic treatments. To get spontaneous mesoscopic evolution of the nanostructures obtained by INCP, a new strategy utilizing a unique conformational change of the conjugated polymer is reported herein. The combination of living ring-opening olefin metathesis polymerization (ROMP) and cyclopolymerization produced block and gradient copolymers through one-pot or one-shot polymerization, which initially formed spherical micelles via INCP. Then, the core block of the micelle stiffened through a coil-to-rod conformational change by simple aging in organic solvents because of cis-to-trans isomerization of the conjugated polymer under light. Subsequently, this enhanced the π-π interaction among the cores, and eventually promoted the growth of stable nanostructures from spheres to 1D-nanocaterpillars or 2D-sheet-like architectures. This time-dependent macroscopic evolution provides deeper insight into the production of a variety of kinetically fixed nano- and mesoscale structures through INCP. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3058–3066     

Ion exchange in reverse micelles

The distribution and dynamics of alkali cations inside Na-AOT reverse micelles have been investigated using Monte Carlo and molecular dynamics simulations. Water is modeled using the extended simple point charge (SPC/E) model. Simulations were carried out for alkali salts of Li+, Na+, K+, and Cs+ placed into the aqueous core of the reverse micelle, for situations corresponding to one and three molecules of added salt. In all cases, we observe that the larger K+ and Cs+ ions exchange with the Na+ counterion; however, the smaller Li+ ion prefers to remains solvated within the core of the reverse micelle. Our study reveals that the oil-water interface of the Na-AOT reverse micelle has the greatest selectivity toward Cs+ followed by K+ and Li+. A model based on enthalpic contributions illustrates that the solvation energies of the different cations in water control the ion-exchange process. The hydration number of the first water shell for Li+ situated in the aqueous core of the reverse micelle with radius R = 14.1 A was similar to that observed at infinite dilution in bulk water.     

Stability of invertase in reverse micelles

The stability of invertase was studied under various conditions, including at 75°C, in presence of stabilizers (sorbitol and glycerol) at 75°C, and in the presence of denaturants (urea and trichloroacetic acid) at 37°C in reverse micelles. Stability of the invertase in reverse micelles was found to be improved over that of the enzyme in bulk aqueous solution. Sorbitol could enhance enzyme stability as it does in the bulk aqueous system. The stabilizing effect of glycerol was reduced in reverse micelles. The denaturation pattern of urea remains unaltered. However, the denaturation effect of trichloroacetic acid has been reduced in reverse micelles.     

Photodetachment of ferrocyanide in reverse micelles

Solvated electrons have been generated in reverse micelles (RMs) through photodetachment of ferrocyanide (Fe(CN)(6)(4-)) in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) RMs. We have measured both bleach recovery of the parent ferrocyanide CN stretch in the infrared and the decay of the solvated electron absorption at 800 nm. The bleach recovery has been fit to a diffusion model for the geminate recombination process. The fit parameters suggest a narrowing of the spatial distribution of ejected electrons due to confinement in the RMs when compared to bulk water. The diffusion coefficient of the solvated electron does not appear to be significantly affected by RM confinement. The decay of the solvated electron absorption exhibits an additional decay component that is not observed in bulk water and is smaller for larger RMs. No corresponding additional component is seen in the parent ferrocyanide IR bleach recovery, which supports our interpretation that the confinement-induced new decay process in RMs is due to electrons reacting with AOT headgroups.     

纳米结构导电聚合物材料研究进展

具有纳米结构的导电聚合物因其诱人的应用前景越来越引起人们的重视。本文综述了聚苯胺、聚吡咯以及聚噻吩等导电聚合物的零维、一维、二维以及三维纳米结构的合成方法,并介绍了聚合物纳米结构的表征以及研究现状和应用前景。参考文献60篇。     

Gelation of spontaneously formed catanionic vesicles by water soluble polymers

The gelation of two spontaneously formed charged catanionic vesicles by four water soluble polymers was systematically studied by tube inversion method and rheology. Eight phase maps were successfully documented for the catanionic vesicle–polymer mixtures. The experimental results, as represented by the relaxation time and the storage modulus at 1 Hz, revealed that the catanionic vesicle–polymer interactions at play were of electrostatic and hydrophobic origin. Firstly, no association between charged catanionic vesicles and the polymer without charge/hydrophobic modification was observed due to lack of both electrostatic and hydrophobic effects. Secondly, hydrophobic interactions accounted for the association between the hydrophobically modified polymer without charge and charged catanionic vesicles with hydrophobic grafts of the polymer inserting in the catanionic vesicle bilayer. Thirdly, the positively charged polymer without hydrophobic modification could interact with negatively charged catanionic vesicles through electrostatic force on one hand but could not interact with positively charged catanionic vesicles on the other hand. Finally, the positively charged polymer with hydrophobic modification could interact both electrostatically and hydrophobically with negatively charged catanionic vesicles, resulting in the formation of strong gels. The hydrophobic interaction might even overcome the unfavorable electrostatic interaction between the positively charged vesicles and the polymer with positive charge/hydrophobic modification.     

Protons in non-ionic aqueous reverse micelles

Using molecular dynamics techniques, we investigate the solvation of an excess proton within an aqueous reverse micelle in vacuo, with the neutral surfactant diethylene glycol monodecyl ether [CH3(CH2)11(OC2H4)2OH]. The simulation experiments were performed using a multistate empirical valence bond Hamiltonian model. Our results show that the stable solvation environments for the excess proton are located in the water-surfactant interface and that its first solvation shell is composed exclusively by water molecules. The relative prevalence of Eigen- versus Zundel-like solvation structures is investigated; compared to bulk results, Zundel-like structures in micelles become somewhat more stable. Characteristic times for the proton translocation jumps have been computed using population relaxation time correlation functions. The micellar rate for proton transfer is approximately 40x smaller than that found in bulk water at ambient conditions. Differences in the computed rates are examined in terms of the hydrogen-bond connectivity involving the first solvation shell of the excess charge with the rest of the micellar environment. Simulation results would indicate that proton transfers are correlated with rare episodes during which the HB connectivity between the first and second solvation shells suffers profound modifications.     

Amide-ligand hydrogen bonding in reverse micelles

One approach to modeling the second coordination shell of metalloproteins is to pair amide-containing counterions with metal complexes to form hydrogen bonds in the solid state. In a more general approach, we have designed a surfactant counterion that can sustain hydrogen bonding interactions with metal complexes in solution. The surfactant is cationic and incorporates an amide as part of its headgroup to form hydrogen. The surfactant forms hydrogen bonding reverse micelles that accommodate anionic metal complexes in their polar core. In reverse micelles containing an iron(III) hexacyanide complex, spectroscopic evidence suggests that the anion is confined to the polar core region in solution. Single-crystal X-ray diffraction data on the surfactant ferricyanide system reveals a layered structure with interdigitated alkyl chains and an extensive network of hydrogen bonds that link amide groups to the cyanide ligands and to neighboring headgroups.     

Phase behavior and properties of reverse vesicles in salt-free catanionic surfactant mixtures

Salt-free 1:1 cationic/anionic (catanionic) surfactant mixture tetradecyltrimethylammonium laurate (TTAL) could be prepared by mixing equimolar tetradecyltrimethylammonium hydroxide (TTAOH) and lauric acid (LA) in water. Given the condition of suitable range of weight fraction of TTAL in total surfactant, rho=WTTAL/(WTTAL+WLA), and at existence of a small amount of water, it was found that the mixtures of so-obtained TTAL and LA could spontaneously form stable reverse vesicles in various organic solvents including toluene, tert-butylbenzene, and cyclohexane. The reverse vesicle phase shows a blue color against room light and exhibits strong birefringence under polarized microscope. The reverse vesicles are very sensitive to temperature change. Increasing temperature could make the rho values within which reverse vesicles were constructed move to higher values. In organic solvents of alkanes such as n-heptane, reverse vesicles could still form but become unstable upon time and centrifugation. Increasing temperature could accelerate phase separation, and finally a gel-like bottom phase was usually observed. Interestingly, the stable reverse vesicles formed by so-called salt-free catanionic surfactant mixtures still show some resistance against adding inorganic salts. They can trap inorganic ions such as Zn2+ and S2- into their hydrophilic layers. This opens the door for template applications of reverse vesicles to prepare inorganic nanoparticles.     

Excited-state proton transfer behavior of 7-hydroxy-4-methylcoumarin in AOT reverse micelles

The excited-state proton transfer and phototautomerization of 7-hydroxy-4-methylcoumarin (7H4MC) dye has been studied in the confined water pools of AOT reverse micelles using steady-state and time-resolved fluorescence measurements. In the "dry" reverse micelles ([water]/[AOT], w(0) = 0), only the neutral form of the dye is present both in the ground and the excited states. At higher w(0) values, three prototropic forms, namely, neutral, anionic, and tautomeric, can be identified in the excited state, although only the neutral form of the dye is present in the ground state. From steady-state fluorescence results and time-resolved area-normalized emission spectra (TRANES), it is indicated that the anionic and tautomeric forms of the dye are the excited-state reaction products and that they arise apparently independently from the excited neutral form of the dye. In bulk water, however, there is no evidence of the tautomeric species and only the anionic form is observed in the excited state. The fluorescence quenching results of the three forms of 7H4MC by the different quenchers, potassium iodide, aniline, and N, N-dimethylaniline, suggest that the distribution of 7H4MC molecules in the reverse micelles is not diverse but that the different prototropic forms arise from the same population of the excited dye in the interfacial region.     

Vibrational dynamics of ice in reverse micelles

The ultrafast vibrational dynamics of HDO:D(2)O ice at 180 K in anionic reverse micelles is studied by midinfrared femtosecond pump-probe spectroscopy. Solutions containing reverse micelles are cooled to low temperatures by a fast-freezing procedure. The heating dynamics of the micellar solutions is studied to characterize the micellar structure. Small reverse micelles with a water content up to approximately 150 water molecules contain an amorphous form of ice that shows remarkably different vibrational dynamics compared to bulk hexagonal ice. The micellar amorphous ice has a much longer vibrational lifetime than bulk hexagonal ice and micellar liquid water. The vibrational lifetime is observed to increase linearly from 0.7 to 4 ps with the resonance frequency ranging from 3100 to 3500 cm(-1). From the pump dependence of the vibrational relaxation the homogeneous linewidth of the amorphous ice is determined (55+/-5 cm(-1)).     

Excited state proton transfer in reverse micelles

The aqueous phase of water/AOT reversed micelles having varying diameters was probed by a single free diffusing proton that was released form a hydrophilic photoacid molecule (2-naphthol-6,8-disulfonate). The fluorescence decay signals were reconstructed through the geminate recombination algorithm, accounting for the reversible nature of the proton-transfer reactions at the surface of the excited molecule and at the water/detergent interface. The radial diffusion of the proton inside the aqueous phase was calculated accounting for both the entropy of dilution and the total electrostatic energy of the ion pair, consisting of the pair-energy and self-energy of the ions. The analysis implied that micellar surface must be modeled with atomic resolution, assuming that the sulfono residue protrudes above the water/hydrocarbon interface by approximately 2 A. The analysis of the fluorescence decay curves implies that the molecule is located in a solvent with physical-chemical properties very similar to bulk water, except for the dielectric constant. For reversed micelles with r(max) > or = 16 A, the dielectric constant of the aqueous phase was approximately 70 and for smaller micelles, where approximately 60% of the water molecule is in contact with the van der Waals surface of the micelle, it is as low as 60. This reduction is a reflection of the increased fraction of water molecule that is in close interaction with the micelle surface.