Interface water-fluorocarbon

If purified poliovirus is not substantially concentrated at a trichloro-trifluoroethane (C2Cl3F3)-water interface, since fluorocarbons are among the most hydrophobic substances known, it is rather improbable that hydrophobic interactions could be involved in poliovirus adsorption to any material. This is particularly true with our oxide surfaces, which in being wet with water, are demonstrated to be hydrophilic in character. This C2CI3F3 extraction procedure is commonly used in enterovirus purification, and is highly effective in removing hydrophobic materials (for example, lipids) from partially purified preparations. 

The Krafft point, the area occupied by a surfactant molecule at the air-water and octane-water interfaces, and the aggregation number of micelles increase with an increase in fluorocarbon and/or hydrocarbon chain length of these hybrid surfactants [209]. The cmc, surface tension, and octane-water interfacial tension at the cmc decrease with an increase in fluorocarbon and/or hydrocarbon chain length. The surfactants lower the surface tension, as well as the hydrocarbon oil-water and the water-fluorocarbon oil interfacial tension. Their solutions in water can float on hydrocarbon liquids, such as benzene, cyclohexane, and decane. The 10% solution of the surfactant with m = 6 and n = 4 chains exhibit rubberlike viscoelasticity [210]. 

Wallace JA, Schiirch S. Line tension of sessile drops placed on a phospholipid monolayer at the water-fluorocarbon interface. Colloids Surfaces 1990 43 207-221. 

The process of adsorption of polyelectrolytes on solid surfaces has been intensively studied because of its importance in technology, including steric stabilization of colloid particles [3,4]. This process has attracted increasing attention because of the recently developed, sophisticated use of polyelectrolyte adsorption alternate layer-by-layer adsorption [7] and stabilization of surfactant monolayers at the air-water interface [26], Surface forces measurement has been performed to study the adsorption process of a negatively charged polymer, poly(styrene sulfonate) (PSS), on a cationic monolayer of fluorocarbon ammonium amphiphilic 1 (Fig. 7) [27],... 

In a PEMFC, the power density and efficiency are limited by three major factors (1) the ohmic overpotential mainly due to the membrane resistance, (2) the activation overpotential due to slow oxygen reduchon reaction at the electrode/membrane interface, and (3) the concentration overpotential due to mass-transport limitations of oxygen to the electrode surfaced Studies of the solubility and concentration of oxygen in different perfluorinated membrane materials show that the oxygen solubility is enhanced in the fluorocarbon (hydrophobic)-rich zones and hence increases with the hydrophobicity of the membrane. The diffusion coefficient is directly related to the water content of the membrane and is thereby enhanced in membranes containing high water content the result indicates that the aqueous phase is predominantly involved in the diffusion pathway. ... 

Lee and Meisel incorporated Py, at levels of 10 M or more, into 1200 EW acid form samples that were swollen with water and with ferf-butyl alcohol. It was concluded based on the /3//1 value for water swollen samples that the Py molecules were located in the water clusters and were most likely near fluorocarbon—water interfaces. It was also concluded, based on both absorption and emission spectra, that the probes had strong interactions with the SO3 groups that were exchanged with Ag+ and Pb + cations in the case of water containing samples. Likewise, the pyrene molecules were rationalized as being surrounded by terf-butanol molecules in that case. However, excimer formation (due to the presence of adjacent pyrene molecules) in the ferf-butyl alcohol system suggested the loss of cluster morphology-... 

S. Marie Bertilla, J.L. Thomas, P. Marie, M.P. Krafft, Co-surfactant effect of a semi-fluorinated alkane at a fluorocarbon/water interface. Impact on the stabilization of fluorocarbon-in-water emulsions, Langmuir 20 (2004) 3920-3924. 

Water-in-fluorocarbon emulsions, stabilised with fluorinated nonionic surfactants, were investigated by small angle neutron scattering (SANS) spectroscopy [8,99]. The results indicated that the continuous oil phase comprised an inverse micellar solution, or water-in-oil microemulsion, with a water content of 5 to 10%. However, there was no evidence of a liquid crystalline layer at the w/o interface. A subsequent study using small angle x-ray scattering (SAXS) spectroscopy gave similar results [100]. 

Amphiphilic molecules, composed of a hydrophilic head group and hydrophobic chain (hydrocarton or fluorocarbon), have a tendency to aggregate at the air/water interface and, when compressed, form monomolecular Langmuir films. These films can be... 

Dendrons attached as side chains on linear polymer chains behave different from free dendrimers and dendrons. Block copolymers, poly(3,5-bis(3,5-bis (benzyloxy)benzyloxy)-benzyl methacrylate-random-methacrylic acid)-block-poly(2-perfluorooctylethyl acrylate), possess poly(benzylether) dendrons and perfluorinated alkyl chains in their side chains (Fig. 4) [85], While an LB film of a copolymer with a medium substitution fraction of poly(benzylether) dendron side chain in poly(methacrylic acid) displays flat surface, a copolymer with high fraction of poly(benzylether) dendron side chains produces the zone texture. Dendron rich blocks are hydrophobic and oleophilic but perfluorinated blocks are solvophobic. Therefore, in this case, the solvophobicity-to-solvophilicity balance must be considered. As a result, copolymers with medium fraction of dendron are laid on solid substrate, but dendron blocks of copolymers with high fraction prefer to arrange at air side of air/ water interface and the fluorocarbon blocks are enforced to exist close to water subphase, resulting in the zone texture [86]. These situations of molecular arrangements at air/water interface are kept even after transfer on solid substrate. By contrast, when perfluorooctadecanoic acids are mixed with block copolymers with high dendron fraction, the flat monolayers are visualized as terrace [87], The monolayers are hierarchized into carboxyl, per-fluoroalkyl, and dendron layers, that is, hydrophilic, solvophobic, and oleophilic layers. In this case, perfluorooctadecanoic acids play a role for ordering of block copolymers. 

A surfactant molecule is an amphiphile, which means it has a hydrophilic (water-soluble) moiety and a hydrophobic (water-insoluble) moiety separable by a mathematical surface. The hydrophobic tails of the most common surfactants are hydrocarbons. Fluorocarbon and perfluorocarbon tails are, however, not unusual. Because of the hydrophobic tail, a surfactant resists forming a molecular solution in water. The molecules will tend to migrate to any water-vapor interface available or, at sufficiently high concentration, the surfactant molecules will spontaneously aggregate into association colloids, i.e., into micelles or liquid crystals. Because of the hydrophilic head, a surfactant (with a hydrocarbon tail) will behave similarly when placed in oil or when put in solution with oil and water mixtures. Some common surfactants are sodium or potassium salts of long-chained fatty acids (soaps), sodium ethyl sulfates and sulfonates (detergents), alkyl polyethoxy alcohols, alkyl ammonium halides, and lecithins or phospholipids. 

Mukerjee, P. and Handa, T. (1981) Adsorption of fluorocarbon and hydrocarbon surfactants to air-water, hexane-water, and perfluorohexane-water interfaces - Relative affinities and fluorocarbon-hydrocarbon nonideahty effects. Journal of Physical Chemistry, 85(15), 2298-2303. 

This relation is found to be only an approximate value for such systems as fluorocarbon-water or hydrocarbon-water interfaces, and not applicable to polar organic liquid-water interfaces. The effect of additives such as n-alkanols on the interfacial tension of aUcane-water interfaces has been investigated in much detail. ... 

On the other hand, it seems that, aside from the overall clustering aspect, little has been discovered, to date, regarding structural features of the polymer itself, particularly from MIR studies. What, for example, can be learned of comonomer sequence distribution, or backbone and sidechain conformations with the accompanying dynamic effects How is conformation affected by counterion type, water content, and temperature, to name a few What can we say about the fluorocarbon/aqueous interface at the molecular level Future studies similiar to those mentioned in the last section may resolve these remaining problems. 

The model of ionic clustering we believe to be most likely at present is that of an approximately spherical, inverted micellar structure. In this model the absorbed water phase separates into approximately spherical domains, and the ion exchange sites are found near the interface, probably imbedded into the water phase. Such a structure satisfies the strong tendency for the sulfonic acid sites to be hydrated, and at the same time this structure will minimize unfavorable interactions between water and the fluorocarbon matrix. 

Figure 5. Cluster-network model for Nafion perfluorinated membranes. The polymeric ions and absorbed electrolyte phase separate from the fluorocarbon backbone into approximately spherical clusters connected by short, narrow channels. The polymeric charges are most likely embedded in the solution near the interface between the electrolyte and fluorocarbon backbone. This configuration minimizes both the hydrophobic interaction of water with the backbone and the electrostatic repulsion of proximate sulfonate groups. The dimensions shown were deduced from experiments. The shaded areas around the interface and inside a channel are the double layer regions from which the hydroxyl ions are excluded electrostatically.

Association of Textile Chemists and Colorists recently [3] described the incorporation of small amoimts of fluorocarbon derivative in a polymeric material normally used to treat textiles for water repellency. They observed that the fluorocarbon preferentially adsorbed at the interfaces and decreased the values to 16 to 18 dynes per cm. Their films clearly showed the ability to self-heal, for when the initially adsorbed layer was deliberately scraped off, additional molecules quickly adsorbed at the interface when the polymer matrix was recured at an elevated temperature. The usefulness of adsorbed films of surface active molecules is thus apparent, and one may expect wide application of this technique to specific problems. The present study, in combination with previous investigations of wettability and surface activity in organic liquids, forms an excellent guide for the design and synthesis of further surface active agents for polymeric systems. 

Figure 6a. 3T3-L1 mouse fibroblasts are shown at fluorocarbon oil-water interfaces 16 h after inoculation. In this photograph, where the cells have not spread but have clustered together in spheroids, the oil received no additive. Continued on next page.

Figure 6b. Mechanical properties of adsorbed BSA layers at a fluorocarbon oil-water interface as a function of the log of the surface concentration of PFBC (0 surface fracture point , surface shear modulus).

When the membrane is placed in liquid water, rearrangement and a phase-transition occur. This could be due to surface rearrangements wherein the fluorocarbon-rich skin of the membrane is repelled from the interface between the water and membrane. What this means is that in order to minimize the energy of the system the side chains and backbone of the polymer reorient so that the chains are now arranged at the membrane/ water interface. This hypothesis agrees with the data that show that the water contact angle on the membrane surface becomes more hydrophilic after the membrane is placed in liquid water [32]. The presence of liquid water also results in the removal of a vapor-liquid meniscus, which could also aid in the above rearrangements [28]. 

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