Fluorinated Gemini Surfactants Research Articles

Photoswitchable adsorption behavior on a silica surface: A comparison of the partially fluorinated surfactants with the hydrocarbon surfactants

The surfactant adsorption at different interfaces is of great importance in surface science. We studied the photoswitchable adsorption/desorption of the partially fluorinated Gemini surfactants (CFS-2, CFS-6) at water-air and quartz-water interfaces. The fluorinated Gemini surfactants exhibit higher surface activity and lower wetting performance for quartz, compared to the comparable hydrocarbon ones (CHS-2, CHS-6). After UV light irradiation, the surface activity of the Gemini surfactants is decreased, and the wetting performances are increased. The adsorption mechanisms of the fluorinated Gemini surfactants at quartz were analyzed using the wetting data. The adsorption of the fluorinated Gemini surfactants at the quartz surface was further investigated by quartz crystal microbalance with dissipation (QCM-D) and AFM. The fluorinated Gemini surfactants exhibit greater adsorption at quartz compared to the comparable hydrocarbon ones. The fluorinated surfactants form rigid films at quartz. Upon UV light irradiation, the fluorinated surfactants exhibit the decreased adsorption at quartz and appear to be desorbed from quartz. The kinetics of the fluorinated surfactant adsorption at quartz was studied using the real-time measurement of QCM-D. Taken together, the findings in the present work provide insight into the significant differences in the surface properties and the adsorption onto the quartz surface between the partially fluorinated surfactants and the hydrocarbon surfactants.

Surface Activity Properties and Aggregation Behaviors of Partially Fluorinated Gemini Surfactants in Aqueous Solution

AbstractThe surface activity and aggregation behavior of partially fluorinated gemini surfactant N,N′‐bis(3‐perfluorohexyl‐2‐hydroxypropyl)‐N,N′‐dipropanesulfonylhexylenediamine (N‐6‐Sul) was studied by surface tension, resonance light scattering and fluorescence spectra measurements. The critical micelle concentration (CMC) values obtained by the three methods are in good agreement. The surface activity parameters such as the effectiveness of surface tension reduction (Πcmc), the maximum surface excess concentration (Γmax) and the minimum surface area per molecule (Amin) were obtained through surface tension curves. The effects of pH, inorganic salts and temperature on the surface activity were also investigated. The morphology and size of the aggregates of N‐6‐Sul were examined by transmission electron microscopy (TEM). The results show that the partially fluorinated gemini surfactant N‐6‐Sul has many advantages such as high surface activity, low CMC value, great salt tolerance and temperature resistance.

Solution Thermodynamics of highly fluorinated gemini bispyridinium surfactants for biomedical applications

Highly fluorinated gemini surfactants are relevant in pharmaceutical field, owing their ability to deliver genes to the respiratory or to the biliar epithelium, where hydrogenated interfering surfactants are present. We report for the first time the thermodynamic properties of the solutions of 1,1′-Bis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-2,2 n-methylenebispyridinium dichloride (n=4, 8, 12). The gene delivery ability of the dichlorides and the structure of the DNA nanoparticles are strictly related to their solution enthalpic properties, resulting in a very sensitive probe of the behaviour of the molecule in solution. Dilution enthalpies, density and sound velocities vs. molality for dichlorides and dimethanesulfonates with different spacer length, n, were measured. The evaluation of apparent and partial molar enthalpies as a function of concentration of the dimethanesulfonate suggests that the effect of the counterion is additive and the values obtained for the hydrogenated surfactants can be transferred to the fluorinated ones, allowing the prediction of enthalpic properties in solution. No evidence of the structure change in solution is found in the trends of volumetric properties vs. m. and the group contribution of the CH2 for both the dichlorides and the dimethanesulfonates results additive as well as the effect of the counterion. The adiabatic molar compressibilities seem to be independent from the counterion and show in micellar region a plateau value much greater than in the case of the more traditional hydrogenated gemini surfactants, indicating a less compact structure of the micelles, probably due to the repulsion between hydrogenated and fluorinated moieties of the molecules.

Novel fluorinated gemini surfactants with γ-butyrolactone segments.

In this work, novel γ-butyrolactone-type monomeric and dimeric (gemini) surfactants with a semifluoroalkyl group [Rf- (CH2)3-; Rf = C4F9, C6F13, C8F17] as the hydrophobic group were successfully synthesized. Dimethyl malonate was dimerized or connected using Br(CH2)sBr (s = 0, 1, 2, 3) to give tetraesters, and they were bis-allylated. Radical addition of fluoroalkyl using Rf-I and an initiator, i.e., 2,2'-azobisisobutyronitrile for C4F9 or di-t-butyl peroxide for C6F13 and C8F17, was perform at high temperature, with prolonged heating, to obtain bis(semifluoroalkyl)-dilactone diesters. These dilactone diesters were hydrolyzed using KOH/EtOH followed by decarboxylation in AcOH to afford γ-butyrolactonetype gemini surfactants. Common 1 + 1 semifluoroalkyl lactone surfactants were synthesized using the same method. Their surfactant properties [critical micelle concentration (CMC), γCMC, pC20, ΓCMC, and AG] were investigated by measuring the surface tension of the γ-hydroxybutyrate form prepared in aqueous tetrabutylammonium hydroxide solution. As expected, the CMC values of the gemini surfactants were more than one order of magnitude smaller than those of the corresponding 1 + 1 surfactants. Other properties also showed the excellent ability of the gemini structure to reduce the surface tension. These surfactants were easily and quantitatively recovered by acidification. The monomeric surfactant was recovered in the γ-hydroxybutyric acid form, and the gemini surfactant as a mixture of γ-butyrolactone and γ-hydroxybutyric acid forms.

Physicochemical Properties of Oleic Acid-Based Partially Fluorinated Gemini Surfactants

We have developed oleic acid-based partially fluorinated gemini surfactants with carboxylic acid headgroups. The fluorocarbon chain is covalently bound to the terminal carbonyl group of oleic acid via a -CH(2)CH(2)OCO- unit, and the carboxylic acid headgroups are introduced to the cis double bond of oleic acid via -OCOCH(2)CH(2)- units. The aqueous solution properties of these surfactants were studied at pH 9 in the presence of 10 mmol dm–3 NaCl by means of static surface tension, pyrene fluorescence, and dynamic light scattering measurements. The resulting surface tension data demonstrate that the partially fluorinated gemini surfactants exhibit excellent surface activity in their dilute aqueous solutions. In addition, the surfactants are suggested to form micellar aggregates 2–4 nm in diameter. We also studied the aqueous temperature-concentration phase diagrams of the partially fluorinated gemini surfactants (disodium salts) on the basis of visual observations (through a crossed polarizer), polarized optical microscopy, and small angle X-ray scattering measurements. Several phase states including micellar solution phase, hexagonal phase, bicontinuous cubic phase, and lamellar phase were observed along with the coexistence of these phases in certain regions. Assemblies with lesser positive curvature tend to be formed with increasing surfactant concentration, increasing temperature, and increasing fluorocarbon chain length. A comparison of the phase diagrams of the partially fluorinated and hydrogenated surfactant systems suggests that close molecular packing is inhibited within the assemblies of the partially fluorinated surfactants because of the limited miscibility between the fluorocarbon and hydrocarbon units. To the best of our knowledge, this is the first systematic report focusing on the temperature-concentration phase diagrams of (partially) fluorinated gemini surfactants over a wide range of compositions and temperatures.

Synthesis of gemini surfactants with twelve symmetric fluorine atoms and one singlet 19F MR signal as novel 19F MRI agents

A family of fluorinated gemini surfactants derived from perfluoropinacol has been synthesized as novel 19F magnetic resonance imaging (19F MRI) agents. These fluorinated surfactants with 12 symmetric fluorine atoms and one singlet 19F MR peak can be conveniently prepared from perfluoropinacol and oligo(ethylene glycols) on multi-gram scales. Solubility, hydrophilicity (log P), and critical micelle concentration (CMC) measurements of these fluorinated surfactants indicated that high aqueous solubility can be achieved by introducing oligo(ethylene glycols) with appropriate length into perfluoropinacol, i.e., manipulating the fluorine content (F%). One of these fluorinated surfactants with high aqueous solubility and excellent 19F MR properties has been identified by 19F MRI phantom experiments as a promising 19F MRI agent.

Aggregation behavior of partially fluorinated Gemini surfactants in aqueous solution: Effect of headgroups

The aggregation behavior of partially fluorinated Gemini surfactants (PFGS) with different headgroups, namely, N,N′-bis[dimethyl-(3-perfluorohexyl-2-hydroxypropyl)ammonium] hexane iodide (2C6FC3-Me), N,N′-bis(3-perfluorohexyl-2-hydroxypropyl) hexylenediamine hydrochloride (2C6FC3-Me.HCl) and N,N′-bis(3-perfluorohexyl-2-hydroxypropyl)-N,N′-dipropanesulfonylhexylenediamine (2C6FC3-Sul) in aqueous solution, were investigated through surface tension and electric conductivity measurements. The surface tension was measured as a function of the concentration at 25, 35 and 45°C, while the electric conductivity was measured at 25, 30, 35, 40 and 45°C. The effect of NaCl on the surface activity was also investigated. In addition, the maximum surface excess concentration (Γmax) and minimum surface area/molecule (Amin) at the air/water interface were estimated by using the Gibbs adsorption isotherm. It was found that the surface activity of 2C6FC3-Sul was superior to that of 2C6FC3-Me and 2C6FC3-Me.HCl. Moreover, thermodynamic parameters (ΔGagg0, ΔHagg0, −TΔSagg0) indicated that the aggregation formation of 2C6FC3-Me.HCl and 2C6FC3-Sul was a process of entropy driving, while the aggregation formation of 2C6FC3-Me was a process of entropy driving at low temperature and a process of enthalpy driving at high temperature. These results demonstrated that aggregation behavior of partially fluorinated Gemini surfactants were strongly affected by headgroups in aqueous solution.

Langmuir isotherm analysis of novel branched per-fluorinated surfactants and their interactions with single stranded DNA

The efficient synthesis and surface properties of new fluorinated gemini surfactants are described. The aim of this study was to investigate the relationships between the molecular structure and the Langmuir layer properties of these fluorinated gemini lipids. The electrostatic ssDNA binding interactions of amino groups included on the spacer were also investigated. The synthesis corresponds to the substitution of vinyl fluorine atom of fluoro-unsaturated esters by a diethylene-oxide diamine via a Michael addition followed by a fluoride elimination reaction. For the spread layers, the measurements of surface pressure versus molecular area were performed with or without ssDNA in the subphase. The monolayers characteristics depend on the hydrophobic chain length, the polar-head, the pH of the subphase and the flexibility of the spacer. The introduction of ssDNA in the subphase seems to show a low interaction between the surfactants and the oligonucleotide.

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Molecular Aggregates of Partially Fluorinated Quaternary Ammonium Salt Gemini Surfactants

The size and shape of novel partially fluorinated gemini surfactant 1,2-bis[dimethyl-(3-perfluoroalkyl-2-hydroxypropyl)ammonium]ethane bromide (CnFC3-2-C3CnF, where n=4, 6, and 8) were investigated in aqueous solution by means of light scattering and transmission electron microscopy (TEM). The sizes of these molecular aggregates changed with increasing carbon number of the alkyl chain and concentration. For example, the apparent hydrodynamic radius by dynamic light scattering was 18 nm at a concentration of cmcx5 for n=4, 115 nm at the cmcx15 for n=6, and 62 nm at the cmcx30 for n=8, at 298.2 K. The shapes of CnFC3-2-C3CnF aggregates drastically changed with the alkyl chain length; the aggregates were mainly in the form of large or irregular small aggregates (n=4), string-like aggregates (n=6), and vesicles (n=8). The bromide-ion activity was measured using a bromide-ion-selective electrode to determine the degree of counterion binding to the aggregates. The degree of counterion binding to aggregate was very small compared with that in the typical hydrogenated gemini surfactants. These results indicated that the small curvature of large aggregates was not influenced by an electrostatic repulsion between the cationic head groups in the case of the bulky molecular volume of fluorinated gemini surfactants.

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.

Equilibrium and Dynamic Surface Tension Properties of Partially Fluorinated Quaternary Ammonium Salt Gemini Surfactants

The equilibrium and dynamic surface tension properties of a partially fluorinated quaternary ammonium salt gemini surfactant 1,2-bis[dimethyl-(3-perfluoroalkyl-2-hydroxypropyl)ammonium]ethane bromide (C(n)(F)C3-2-C3C(n)F, where n represents fluorocarbon chain lengths of 4, 6, and 8) were investigated, and the effects of the fluorocarbon chain length and the number of chains on them were discussed. The plot of the logarithm of the critical micelle concentration (cmc) against the fluorocarbon chain length for C(n)(F)C3-2-C3C(n)F showed a linear decrease with an increase in chain length. On the basis of the slope of this plot, it was found that the variation in cmc with respect to the chain length is large for fluorinated gemini surfactants. The surface tension at the cmc decreased significantly; this surface tension value is lower than that of conventional fluorinated monomeric surfactants. In particular, the lowest value was 13.7 mN m(-1) for n = 8. Furthermore, it was confirmed that the kinetics of adsorption at the interface decrease with an increase in the fluorocarbon chain length and the concentration.