New mesogen with thermotropic cubic phase: 3,4,5‐tris‐(11,11,12,12,13,13,14,14,15,15,16,16,16‐tridecafluorohexadecyloxy)benzoic acid

A new mesogen, 3,4,5‐tris(11,11,12,12,13,13,14,14,15,15,16,16,16‐tridecafluoro‐hexadecyloxy)benzoic acid, with a thermotropic cubic phase was synthesized. The phase behaviour of the fluorinated compound and its corresponding non‐fluorinated analogue was investigated by differential scanning calorimetry, polarizing optical microscopy, and synchrotron small‐angle X‐ray diffraction. The fluorinated compound, which contains three partially perfluorinated alkoxy moieties and one carboxylic acid group capable of forming hydrogen bonding, exhibits a very interesting sequence of isotropic, cubic and hexagonal columnar phases, whereas its non‐fluorinated compound does not have a liquid crystalline phase. The cubic phase exists over a wide temperature range (from ～200°C to ～30°C on cooling) and is hence amenable to various physical measurements and potential applications. The ability to self‐assemble molecules into ordered superstructure via both partially perfluorinated chains and hydrogen bonding provides new insight for the development of novel liquid crystalline materials.     

Mixing behavior of fluorinated and hydrogenated gemini surfactants at the air-water interface

Mixing behavior of hydrogenated and fluorinated cationic gemini surfactants was studied at the air-water interface by Brewster angle microscopy and pi-A isotherm curves. In the bulk, these two molecules did not mix and showed phase separation. At the air-water interface, if a monolayer was formed by separate deposition of the two solutions, they formed separate domains, and the compression occurred in two steps: first the domains with hydrogenated gemini surfactant were compressed until they showed collapse; then the domains with fluorinated gemini surfactant were compressed. If the two solutions were mixed before the deposition, they remained mixed upon compression; on the other hand, separate domains under separate deposition were shown to mix if the subphase was heated.     

Strategies for synthesizing non-bioaccumulable alternatives to PFOA and PFOS

This minireview describes the strategies for synthesis of fiuorinated surfactants potentially nonbioaccumulable.Various strategies have been focused on(Ⅰ) reducing the length of the perfluorocarbon chain,(Ⅱ) introducing hetero atoms into the fluorocarbon chain,(Ⅲ) introducing branch(herein and after branch means the fluoro-carbon chain section is not straight).In most cases,the surface tensions versus the surfactant concentrations have been assessed.These above strategies led to various highly fiuorinated(perfluorinated or not perfluorinated) surfactants whose chemical changes enabled to obtain novel alternatives to perfluorooctanoic acid(PFOA) and perfluorooctane sulphonate(PFOS).     

以全氟丁基为基础的具有高表面活性的氟表面活性剂

氟表面活性剂的环境和生物降解问题是最近的热点, 特别是全氟长链(≥C8)氟表面活性剂的应用限制乃至禁用已成为必然趋势. 本文合成了一种以短链的全氟丁基为基础的阳离子氟表面活性剂, N-[3-(二甲基胺基)丙基]全氟丁基磺酰胺盐酸盐(C4F9SO2NH(CH2)3NH(CH3)+2Cl-, 简称为PFB-MC). 该表面活性剂适用于强酸性环境, 具有极高的表面活性, 其溶液最低表面张力(19.80 mN·m-1)和通常的氟表面活性剂相当. 通过表面张力方法得到了固定pH(pH=2.6-2.7)情况下PFB-MC的表面张力-浓度对数(γ-lgc)曲线, 以及该pH下外加盐([NaCl]=0.1 mol·L-1)对表面张力的影响; 并进一步研究了pH对PFB-MC在其临界胶束浓度(cmc)前后的表面张力的影响.     

Synthesis and properties of a novel class of gemini pyridinium surfactants

A novel class of gemini pyridinium surfactants with a four-methylene spacer group was synthesized, and their surface-active properties and interactions with polyacrylamide (PAM) were evaluated by surface tension, fluorescence, and viscosity measurements. A comparison between the gemini pyridinium surfactants and their corresponding monomers was also made. The cmc's of gemini pyridinium surfactants are much lower than those of the corresponding monomeric surfactants. The C20 value is about one order of magnitude lower than that of corresponding monomers, and the longer the hydrophobic chains of the surfactants, the lower the cmc value. Surface tension measurements of the surfactant-PAM mixed systems show that the critical aggregation concentration (cac) value is much lower than the cmc value of the surfactant system alone. Viscosity measurements of the surfactant-PAM mixed systems show that the relative viscosity of the surfactant-PAM system decreased with increasing concentration of surfactant. Additionally, fluorescence measurements of the surfactant-PAM mixed system suggest the formation of surfactant-polymer aggregates, and the gemini pyridinium surfactant with longer hydrophobic chains have a stronger interaction with PAM, owing to the stronger hydrophobic interaction.     

Hybrid fluorocarbon-hydrocarbon CO2-philic surfactants. 1. synthesis and properties of aqueous solutions

Six different hybrid fluorocarbon-hydrocarbon (F-H) sulfate and sulfonate surfactants, with variations in the relative F/H carbon chain length, have been synthesized and characterized in aqueous solution. These compounds have been targeted for potential activity in densified CO2. Tensiometric data and chemical analyses were consistent with surfactants of high chemical purity. Fluorination in terms of the F/H ratio exerts a strong control over all the surfactant physicochemical properties, including critical micelle concentrations (cmc's) and adsorption isotherms. One of these partially fluorinated surfactants (the sulfonate phi-F6H4) achieves very low surface tensions in water (gamma(cmc) approximately 19 mN m(-1)) more reminiscent of fully fluorinated double-chain compounds. Detailed 19F NMR studies revealed that omega'-CF3 groups can exhibit separate signals for monomeric and micellized forms, hence facilitating cmc determinations. Small-angle neutron scattering investigations confirmed the presence of ellipsoidal or extended disklike micelles, depending on the F-H chain asymmetry. For example, a symmetric hybrid F8H8 generates disklike micelles, whereas chain asymmetry in F8H4 or phi-F6H4 tends to drive cylindrical aggregation structures. These changes are consistent with variations in the surfactant packing parameter caused by the different chain F/H ratios. Hence, adsorption and aggregation are shown to respond in a predictable way to the molecular structure of these unusual surfactants.     

Formation of vesicles in block copolymer-fluorinated surfactant complexes

Spherical micellar aggregates have been obtained in chloroform by mixing poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers with perfluorinated surfactants (FS) bearing a carboxylic acid head. These micellar aggregates are resulting from the self-assembly of the insoluble P4VP/fluorinated complexes into a core surrounded by the soluble PS coronal chains. Their characteristic features have been studied as a function of various parameters including the composition of the PS-b-P4VP copolymer, the tail length of the fluorinated surfactant, the 4VP/FS molar ratio, the number of carboxylic acid group (1 or 2) on the surfactant, the presence of the PS block and of the fluorine atoms on the surfactant. Dilution of these initial micellar aggregates triggers a morphological reorganization resulting in the formation of more stable vesicles. The extent of this morphological transition is related to the solubility of the P4VP/fluorinated complexes during the dilution process. This transition is complete for short P4VP/FS complexes, incomplete for long P4VP/FS complexes, and not observed whenever an alpha,omega-difunctional FS is used in P4VP/FS complexes, leading to a cross-linked core. Finally, the spheres-to-vesicles transition has been advantageously used in order to encapsulate molecules, as demonstrated by confocal fluorescence microscopy.     

The unusual micelle micropolarity of partially fluorinated gemini surfactants sensed by pyrene fluorescence

New gemini surfactants having two fluorocarbon chains were prepared by refluxing partially fluorinated alkyl bromide with N,N,N',N'-tetramethyl-1,6-diaminohexane in acetonitrile. The partially fluorinated gemini surfactants containing a six-methylene spacer chain are easily soluble in water. The critical micelle concentrations (cmc's) were determined by various fluorescent probe methods. The hydrophobicity of a CF2 group was estimated to be 1.5 times that of a CH2 group according to the cmc values. The micelle micropolarity of a fluorocarbon gemini sensed by pyrene fluorescence was unusually high, suggesting an apparent iceberg-like environment in the location of pyrene. The significantly small micelle aggregation numbers of fluorinated gemini surfactants were ascertained by the pyrene fluorescence quenching method. The micelle ionization degree estimated by fluorescence quenching of 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) gave tendencies similar to those of the corresponding hydrocarbon geminis.     

Molecular-thermodynamic theory of micellization of multicomponent surfactant mixtures: 1. Conventional (pH-Insensitive) surfactants

A molecular-thermodynamic (MT) theory was developed to model the micellization of mixtures containing an arbitrary number of conventional (pH-insensitive) surfactants. The theory was validated by comparing predicted and experimental cmc's of ternary surfactant mixtures, yielding results that were comparable to, and sometimes better than, the cmc's determined using regular solution theory. The theory was also used to model a commercial nonionic surfactant (Genapol UD-079), which was modeled as a mixture of 16 surfactant components. The predicted cmc agreed well with the experimental cmc, and the monomer concentration was predicted to increase significantly above the cmc. In addition, the monomer and the micelle compositions were predicted to vary significantly with surfactant concentration. These composition variations were rationalized in terms of competing steric and entropic effects and a micelle shape transition near the cmc. To understand the packing constraints imposed on ternary surfactant mixtures better, the maximum micelle radius was also examined theoretically. The MT theory presented here represents the first molecular-based theory of the micellization behavior of mixtures of three or more conventional surfactants. In article 2 of this series, the MT theory will be extended to model the micellization of mixtures of conventional and pH-sensitive surfactants.     

Mixed micelles of fluorocarbon and hydrocarbon surfactants. A small angle neutron scattering study

Mixtures of the partly fluorinated cationic surfactant HFDePC (N-(1, 1,2,2-tetrahydroperfluorodecanyl)-pyridinium chloride and deuterated headgroup) with C16TAC, hexadecyl-trimethylammonium chloride, have been investigated using small angle neutron scattering with contrast matching. Earlier results from this system suggested that a demixing occurred, into two coexisting populations of micelles, hydrocarbon-rich and fluorocarbon-rich, respectively. The present results could be explained by one type of mixed micelles with an inhomogeneous distribution of fluorinated and hydrogenated surfactants within the micelles although a demixing cannot be definitely excluded.     

Synthesis and surface properties of new semi-fluorinated sulfobetaines potentially usable for 2D-electrophoresis

New semi-fluorinated amidosulfobetaines, homologs of hydrocarbon amidosulfobetaines (ASB) commonly used in two-dimensional gel electrophoresis (2DE), were prepared in three steps from 2-F-alkylethyl iodide or F-alkyl iodide. Their synthesis was described and their air-water interface properties were investigated and compared with their perhydrogenated counterpart properties. The influence of the relative lengths of the perfluorinated and hydocarbonated moieties was discussed. 2DE of a rat testicular membrane fraction was performed comparatively using one of these fluorinated sulfobetaines and its hydrocarbon homolog; these preliminary results showed the great potential of the semi-fluorinated sulfobetaines in proteomic analysis.     

Molecular dynamics simulation of a reverse micelle self assembly in supercritical CO2

In this communication we report on molecular dynamics computer simulations of self-assembly of reverse micelles in supercritical carbon dioxide. The reverse micelles contain perfluoropolyether ammonium carboxylate surfactants and an aqueous core. We observed a quick self-assembly of these micelles over time periods of approximately 5 ns, irrespective of initial conditions. In most cases, the self-assembled perfluorinated reverse micelles have a nice spherical shape and properties consistent with experiments. When the fluorinated surfactant is replaced by its hydrogenated analogue, the assembled aggregate contains a region of direct contact between water and carbon dioxide, indicating that hydrogenated surfactant is not a good agent for creation of microemulsions in water/carbon dioxide mixtures.     

Mixed fluorinated-hydrogenated surfactant-based system: preparation of ordered mesoporous materials

We have investigated a mixed fluorinated-hydrogenated surfactant-based system [C8F17C2H4(OC2H4)9-C12H25(OC2H4)8] in water. The phase diagram exhibits that the micellar domain can be divided into three parts: above 80 wt% of water both hydrogenated and fluorinated surfactants are completely miscible and they formed mixed micelles in all proportion. When the water concentration is decreased from 80 to 60 wt% a gap of miscibility appears and two micellar zones, one fluorocarbon-rich micelles and one hydrocarbon-rich micelles are observed. The liquid crystal domain is composed of one fluorocarbon-rich (H(F)(1)) and one hydrocarbon-rich (H(H)(1)) hexagonal phase. The hydrophobic radius and the cross-sectional area remain constant in the H(H)(1) and in the H(F)(1) domains. Moreover, SAXS measurements proved that the hydrophobic chains in the liquid crystal phases adopt rather an extended conformation. Then the mixture of surfactants was used as template for the preparation of mesoporous materials. Mesostructured silicas with a well hexagonal array of their channels were prepared via a cooperative templating mechanism (CTM), if the loading of fluorinated surfactant is larger than 50%. Decreasing the proportion of the fluorinated amphiphile in the mixture leads to the formation of mesoporous silica with a disordered structure. In this case the channel arrangement is no longer governed by the fluorinated surfactant but by the hydrogenated one.     

Interaction of Fluorocarbon Containing Hydrophobically Mdified Polyelectrolyte with Nonionic Surfactants

The interaction of fluorocarbon containing hydrophobically modified polyelectrolyte(FMPAANa) with two kinds of nonionic surfactants(hydrogenated and fluorinated)in a semidilute (0.5wt%) aqueous solution had been studied by rheological measurements,Association behavior was found in both systems.The hydrophobic interaction of FMPAANa with fluorinated surfactant(FC171) is much stronger than that with hydrogenated surfactant(NP7.5) at low surfactoant concentrations.The interaction is strengthened by surfactants being added for the density of active junctions increased.Whereas distinct phenomena for FC171 and NP7.5 start to be found as the surfactants added over their respective certain concentration.The interaction of polyelectrolyte with fluorinated surfactant increases dramatical ly while that with hydrogenated surfactant decreases.     

Interaction of Fluorocarbon Containing Hydrophobically Modified Polyelectrolyte with Nonionic Surfactants

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Segregation phenomena in micelles from mixtures of fluorinated and hydrogenated surfactants

Mixtures of hydrogenated and fluorinated surfactants are known to form either mixed or segregated micelles: the conclusions are much dependant on the precision of the experimental measurements and on the model used for interpretation. Recently, mixed surfactant solutions were probed at the micellar or molecular level by SANS, fluorescence or NMR. It leads to an intermediate structure for the mixed micelles with an intramicellar segregation of the fluorinated and hydrogenated surfactant.This intramicellar segregation was also observed in a variety of more complex systems which are rapidly surveyed in the second part.     

Free‐radical polymerization of dioxolane and dioxane derivatives: Effect of fluorine substituents on the ring opening polymerization

Partially fluorinated and perfluorinated dioxolane and dioxane derivatives have been prepared to investigate the effect of fluorine substituents on their free‐radical polymerization products. The partially fluorinated monomer 2‐difluoromethylene‐1,3‐dioxolane (I) was readily polymerized with free‐radical initiators azobisisobutyronitrile or tri(n‐butyl)borane–air and yielded a vinyl addition product. However, the hydrocarbon analogue, 2‐methylene‐1,3‐dioxolane (II), produced as much as 50% ring opening product at 60 °C by free‐radical polymerization. 2‐Difluoromethylene‐4‐methyl‐1,3‐dioxolane (III) was synthesized and its free‐radical polymerization yielded ring opening products: 28% at 60 °C, decreasing to 7 and 4% at 0 °C and −78 °C, respectively. All the fluorine‐substituted, perfluoro‐2‐methylene‐4‐methyl‐1,3‐dioxolane (IV) produced only a vinyl addition product with perfluorobenzoylperoxide as an initiator. The six‐membered ring monomer, 2‐methylene‐1,3‐dioxane (V), caused more than 50% ring opening during free‐radical polymerization. However, the partially fluorinated analogue, 2‐difluoromethylene‐1,3‐dioxane (VI), produced only 22% ring opening product with free‐radical polymerization and the perfluorinated compound, perfluoro‐2‐methylene‐1,3‐dioxane (VII), yielded only the vinyl addition polymer. The ring opening reaction and the vinyl addition steps during the free‐radical polymerization of these monomers are competitive reactions. We discuss the reaction mechanism of the ring opening and vinyl addition polymerizations of these partially fluorinated and perfluorinated dioxolane and dioxane derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5180–5188, 2004     

Determination of trace levels of total fluorine in water using combustion ion chromatography for fluorine: a mass balance approach to determine individual perfluorinated chemicals in water

Perfluorinated compounds (PFCs) such as perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) have received worldwide attention because of their environmental persistence and widespread distribution. Because of the lack of robust analytical methods and standards to detect all of the PFCs, and their precursors and metabolic intermediates, a mass balance approach involving the determination of total fluorine (TF), followed by fractionation of samples to separately determine inorganic and organic fluorine, is needed. In this study, we have developed a method to determine low microg/L levels of total fluorine (TF) in seawater samples. Further, seawater samples were fractionated into organic and inorganic fractions by extraction with organic solvents, which were then analyzed for TF, extractable organic fluorine (EOF) and inorganic fluorine (IF; i.e., fluoride). Concentrations of known perfluorinated compounds (PFCs) including PFOS and PFOA were also determined in water samples by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to enable calculation of the fraction of fluorine that is contributed by PFCs to TF. A major proportion of fluorine in seawater was in the form of fluoride (>90% in locations not affected by direct discharges). Nevertheless, within the organofluorine fraction, a major percentage (60-90%) of fluorine still remains unknown in water samples, suggesting the occurrence of other fluorinated acids in addition to known perfluorinated acids. Further studies are needed to identify and quantify the unidentified organofluorines in seawater. Mass balance analysis of total organic fluorine (TOF) and EOF is important, if we are to understand transport and fate of fluorinated compounds in the environment, and if we are to identify the sources of unidentified fluorinated compounds.