Investigation in monolayers of double-chain fluorocarbon amphiphiles Effect of headgroups on molecular packing and interaction between hydrocarbon and fluorocarbon monolayers

The surface pressure-area diagrams of double-chain fluorocarbon amphiphiles with different headgroup compositions show that the amphiphiles arrange almost perpendicularly to the water subphase and the structure of headgroups exerts significant influence on the amphiphile packing. Strong hydrogen bonding and weak electrostatic interaction favor the formation of stable monolayers. Perfluorooctanoic acid (FOA) cannot form monolayer at water/air interface and can only form liquid monolayer in subphase of calcium nitrate solution. Complete phase separation of palmitic acid and a fluorocarbon amphiphile with shorter hydrocarbon spacer group, 1, could be demonstrated in monolayers by using the phase rule of Crisp. The creation of phase-separated monolayers is possible when the monolayer is composed of a mixture of palmitic acid and a fluorocarbon amphiphile with longer hydrocarbon spacer group, 2. It can be suggested that the miscibility of hydrocarbon amphiphiles with fluorocarbon amphiphiles is determined by the hydrocarbon fraction of fluorocarbon amphiphiles.     

Separation of fluorinated amino acids and oligopeptides from their non-fluorinated counterparts using high-performance liquid chromatography

Chromatographic conditions for the separation of fluorinated amino acids and oligopeptides from their non-fluorinated counterparts were explored. The separation of six pairs of analytes, including both aromatic and aliphatic fluorocarbons, was investigated at various temperatures using both hydrocarbon and fluorocarbon columns and eluents. Our results show that when hydrocarbon eluents are used, fluorocarbon column provides better separation of fluorinated amino acids or oligopeptides from their non-fluorinated counterparts; when fluorocarbon eluents are used, hydrocarbon column provides better separation of fluorinated amino acids or oligopeptides from their non-fluorinated counterparts. These chromatographic behaviors reflect the fluorophilicity possessed by fluorinated amino acids and oligopeptides.     

Prediction of conformational characteristics and micellar solution properties of fluorocarbon surfactants

A molecular-thermodynamic theory is developed to model the micellization of fluorocarbon surfactants in aqueous solutions, by combining a molecular model that evaluates the free energy of micellization of fluorocarbon surfactant micelles with a previously developed thermodynamic framework describing the free energy of the micellar solution. In the molecular model of micellization developed, a single-chain mean-field theory is combined with an appropriate rotational isomeric state model of fluorocarbon chains to describe the packing of the fluorocarbon surfactant tails inside the micelle core. Utilizing this single-chain mean-field theory, the packing free energies of fluorocarbon surfactants are evaluated and compared with those of their hydrocarbon analogues. We find that the greater rigidity of the fluorocarbon chain promotes its packing in micellar aggregates of low curvatures, such as bilayers. In addition, the mean-field approach is utilized to predict the average conformational characteristics (specifically, the bond order parameters) of fluorocarbon and hydrocarbon surfactant tails within the micelle core, and the predictions are found to agree well with the available experimental results. The electrostatic effects in fluorocarbon ionic surfactant micelles are modeled by allowing for counterion binding onto the charged micelle surface, which accounts explicitly for the effect of the counterion type on the micellar solution properties. In addition, a theoretical formulation is developed to evaluate the free energy of micellization and the size distribution of finite disklike micelles, which often form in the case of fluorocarbon surfactants. We find that, compared to their hydrocarbon analogues, fluorocarbon surfactants exhibit a greater tendency to form cylindrical or disklike micelles, as a result of their larger molecular volume as well as due to the greater conformational rigidity of the fluorocarbon tails. The molecular-thermodynamic theory developed is then applied to several ionic fluorocarbon surfactant-electrolyte systems, including perfluoroalkanoates and perfluorosulfonates with added LiCl or NH(4)Cl, and various micellar solution properties, including critical micelle concentrations (cmc's), optimal micelle shapes, and average micelle aggregation numbers, are predicted. The predicted micellar solution properties agree reasonably well with the available experimental results.     

正、负离子碳氟-碳氢表面活性剂混合水溶液的表面活性

1　前言碳氟表面活性剂是目前所有表面活性剂中表面活性最高的一类 ,具有很多碳氢表面活性剂无法取代的特殊用途[1] 。但是碳氟表面活性剂由于合成困难 ,价格昂贵 ,实际应用受到限大限制。研究表明 ,通过碳氟表面活性剂与碳氢表面活性剂的复配 ,有可能减少碳氟表面活性剂的用量而保持其表面活性 [1] 。在所有表面活性剂混合体系中 ,正、负离子表面活性剂混合体系具有最强的协同效应 [2 ] 。但由于正、负离子表面活性剂混合溶液一般在很低浓度即形成沉淀 ,对碳氟表面活性剂更是如此。因此目前有关碳氟—碳氢混合表面活性剂的研究主要集中在同…     

Quantum chemistry studies of unbranched fluoropolymers

The results of quantum chemistry calculations of energy and topology parameters, vibration and NMR spectra of model fluorocarbon and unbranched hydrocarbon molecules are presented in this work. The formation of radicals and branches in fluorocarbon molecules and mechanisms of hydrogen substitution by fluorine at fluorination of hydrocarbon paraffins and polymers are discussed based on obtained results.     

Polymerized micelles with compartments

Multicompartment micelles with distinct hydrophobic microdomains having different properties have been realized via micellar polymers bearing hydrocarbon and fluorocarbon fragments. In aqueous solution, such polymers can self-organize into coexisting hydrocarbon and fluorocarbon microdomains that selectively solubilize different hydrophobes. The most efficient approach uses block copolymer polysoaps, but simpler designs may be possible.     

Synthesis and self-assembly of an amino-functionalized hybrid hydrocarbon/fluorocarbon double-chain phospholipid

In this article, we designed and synthesized an amino-functionalized hybrid hydrocarbon/fluorocarbon double-chain phospholipid (ACFPC) containing one chain with the hydrophobic fluorocarbon chain and terminal amino, amide, and ether linkages and one chain with the hydrocarbon chain. The novel reactive phospholipid was fully characterized with Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), and mass spectrometry (MS). Then the self-assembly behaviors of the hybrid double-chain phospholipid in aqueous and acidic media were investigated with transmission electron microscopy (TEM), the critical micelle concentration (cmc), dynamic light scattering (DLS), and the hydrocarbon double-chain phospholipid (ACCPC) for comparison. Moreover, their self-assembled structures in aqueous and acidic media were simulated using the dissipative particle dynamics (DPD) method. These results suggest that the fluorocarbon/hydrocarbon hybrid-chain phospholipid can self-assemble into a more stable microstructure compared to the double hydrocarbon chain phospholipid, which will have the potential ability to self-assemble into a more stable minicking biomembrane structure onto material surfaces to inhibit protein adsorption under complicated physiological conditions.     

Solid state crystalline and liquid crystalline structure of semifluorinated 1-bromoalkane compounds

A series of semifluorinated 1-bromoalkane (SFBA) mesogens have been synthesized and characterized to better understand their solid state crystalline and liquid crystalline structures. In the solid state, the local conformation of the fluorocarbon segments becomes disordered once the fluorocarbon chain reaches a length above eight CF units. This is evident from the pronounced decrease of molar melting enthalpy. An increasing amount of helix and helix reverse conformations and increasingly disordered packing can also be observed with each addition of a fluorocarbon segment. X-ray diffraction peaks in the small angle region can be indexed by a tilted, two dimensional layered (herring bone) structure. The crystal structure is similar to a type of plastic crystal in which the amphiphilic character is clear, because the two segments of fluorocarbon and hydrocarbon are almost immiscible. Heating of F(CF2)12(CH2)10Br leads to a transition from plastic crystal to smectic B, as revealed by time-resolved XRD and FTIR analysis. At this solid-to-liquid transition temperature, conformational analysis confirmed an onset of the CH2 gauche conformation within the hexagonal lattice, most likely due to changes occurring in the hydrocarbon segment, and a sudden increase of helix defects along the fluorocarbon segment. The disordered helix rigid-rod structure of the fluorocarbon segment and its poor compatibility with the hydrocarbon segment play an important role in the crystalline solid and liquid crystalline structures.     

碳氟-碳氢表面活性剂混合水溶液在油面上铺展

本文研究RfCONH(CH2)3N(C2H5)2CH3I/CnH2n 1,COONa及RfCOONa/CmH2m 1N(CH3)3Br(Rf=F[CF(CF3)CF2O]2CF(CF3);n=7,8.11,13;m=8,10,12)两类正，负离子碳氟－碳氢表面活性剂混合水溶液在油面上的铺展及对油面的密封性能。研究表明在碳氟表面活性剂中加入异电性碳氢表面活性剂可大大降低碳氟表面活性剂水溶液的铺展浓度，也可使一些因素表面张力较高而不能铺展的碳氟表面活性剂水溶液在油面上铺展。在碳氟表面活性剂中加入异电性碳氢表面活性剂可提高水膜对油面的密封性。若在混合表面活性剂中加入黄原胶，水膜的密封性能更好。     

Distribution of fluorocarbon quencher among micelles via pyrene fluorescence probe method

 Fluorescence-quenching of pyrene in micellar system has been investigated using 1,1,2,2-tetrahydroheptadecafluorodecylpyridinium chloride (HFDePC). The new fluorocarbon quencher has a similar quenching ability as hexadecyl-pyridinium chloride (CPC) towards pyrene in hydrocarbon micelles if only a quencher molecule is solubilized in a micelle. The fluorocarbon quencher randomly distributed among micelles if the average occupancy number of probes per a micelle was small enough. The fluorescence behavior of pyrene was examined for hexadecyl-trimethylammonium chloride (CTAC) and HFDePC mixtures. The variation of fluorescence intensity gave second cmc, reflecting the micellar immiscibility of fluorocarbon and hydrocarbon surfactants. The second cmc can be simulated by material balances of both surfactants supposing the coexistence of two kinds of mixed micelles. The fluorescence-quenching behavior suggested the enhanced micellar immiscibility probably due to nonrandom distribution of fluorocarbon quenchers among micelles. Received: 13 March 1997 Accepted: 24 May 1997     

Characteristics of mixed bilayers of surfactants formed on alumina

The interaction between hydrocarbon and fluorocarbon surfactants on-alumina has been studied through the dispersion behavior of-alumina. When a low concentration of anionic hydrocarbon or fluorocarbon surfactant as a first additive is added to positively charged alumina, the alumina flocculates. The flocculated alumina redisperses upon addition of different surfactant from the first one by the manner that the hydrophobic parts of hydrocarbon and fluorocarbon surfactants are in contact with hydrophobic parts of the first surfactants and the hydrophilic polar groups direct out to liquid phase, resulting in the formation of mixed bilayers on the alumina. From the measurements of mean particle size, zeta potential of the alumina, and adsorbed amount of surfactants, the mixed bilayers consisting of anionic fluorocarbon-noniomc hydrocarbon surfactants and of anionic fluorocarbon-noioic hydrocarbon ones are found to be formed more preferentially than anionic hydrocarbon-anioic fluorocarbon surfactants. The property of the mixed bilayer on the alumina is also discussed using the fluorescence spectra of pyrene.     

Synthesis and solid state structure of fluorous probe molecules for fluorous separation applications

A series of colored hydrocarbon and fluorocarbon tagged 1-fluoro-4-alkylamino-anthraquinones and 1,4-bis-alkylamino-anthraquinone probe molecules were synthesized from a (fluorinated) alkyl amine and 1,4-difluoroanthraquinone to aid in the development of fluorous separation applications. The anthraquinones displayed stacking of the anthraquinone tricycle and interdigitation of the (fluorinated) alkyl chains in the solid state. Furthermore, intramolecular N-H?O hydrogen bonds forced the hydrocarbon and fluorocarbon tags into a conformation pointing away from the anthraquinone tricycle, with the angle of the tricycle plane normal and the main (fluorinated) alkyl vector ranging from 1° to 39°. Separation of the probe molecules on fluorous silica gel showed that the degree of fluorination of the probe molecules plays only a minor role with most eluents (e.g., hexane/ethyl acetate and methyl nonafluorobutyl ethers/ethyl acetate). However, toluene as eluent caused a pronounced separation by degree of fluorination for fluorocarbon, but not hydrocarbon tagged probe molecules on both silica gel and fluorous silica gel. These studies suggest that hydrocarbon and fluorocarbon tagged anthraquinones are useful probe molecules for the development of laboratory scale fluorous separation applications.     

Homogeneous catalysis,heterogeneous recycling: a new family of branched molecules with hydrocarbon or fluorocarbon chains for the Friedländer synthesis of quinoline under solvent-free conditions

A new family of branched catalysts with hydrocarbon or fluorocarbon chains was used to catalyze Friedländer reaction between 2-aminoarylketones and α-methylene ketones under solvent-free conditions in good to excellent yields. The catalysts exhibit temperature-dependent solubility and such a thermomorphic character allows them to be recovered by filtration conveniently at room temperature and reused at least five times. To some extent, the branched catalysts with hydrocarbon chains are superior to those with fluorocarbon chains, as they are cheaper and more biodegradable.     

Probing the impact of advanced melting and advanced adsorption phenomena on the accuracy of pore size distributions from cryoporometry and adsorption using NMR relaxometry and diffusometry

The penetration of compressed CO(2) in hydrocarbon and fluorocarbon regions of concentrated surfactant mesophases are interpreted from differences in the CO(2)-processed pore expansion of mesoporous silica thin films templated by three surfactants containing varying degrees of hydrocarbon and fluorocarbon functionality. Ordered silica thin films are synthesized for the first time using the 16-carbon (C(16)) partly fluorinated surfactant, 11,11,12,12,13,13,14,14,15,15,16,16,16-tridecafluorocetyl pyridinium bromide (HFCPB), as a templating agent. Silica films templated with surfactants containing a 8-carbon (C(8)) fluorocarbon tail (3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl pyridinium chloride (HFOPC)) and a 16-carbon (C(16)) hydrocarbon tail (cetyl pyridinium bromide (CPB)) and HFCPB (C(16)) are processed in compressed CO(2) (69-172 bar, 25 °C and 45 °C) during synthesis. CO(2) processing results in significant pore expansion for films templated with both fluorinated surfactants, while pore expansion is negligible for the hydrocarbon templated material suggesting that preferential CO(2) penetration occurs in the 'CO(2)-philic' fluorocarbon segments of the surfactant template. The effect of substrate surface energy on the final uniformity of the dip-coated films is studied by varying the substrate from unmodified glass to a fluorocarbon-capped substrate. The ability to create dip-coated thin films on low surface energy substrates through favorable interaction of surfactant template tail with the substrate surface functional groups is demonstrated.     

Synthesis of associating poly(acrylic acid) in supercritical carbon dioxide and its solution properties

Hydrophobically associating polymers have been synthesized in supercritical carbon dioxide by copolymerization of acrylic acid with different amounts of acrylate with hydrocarbon or fluorocarbon groups. It was found that conversion of hydrocarbon comonomers was above 95% whereas that for fluorocarbon comonomers was only about 50%. In addition, large amounts of hydrophobic groups could be easily introduced to poly(acrylic acid) by reaction in supercritical carbon dioxide. The solution properties were investigated by rheology. The results indicated that intermolecular association of the copolymer was strong and viscosity was maximum under acidic conditions. In aqueous solutions fluorocarbon hydrophobes associated much more strongly than the hydrocarbon variety, but the viscosifying effect of PAAC-18 series copolymers in 2% (w/w) solution was more pronounced than that of the PAAF series, results which did not agree with the conclusions of Ravey and Stébé. It was also found that the thixotropy behavior of copolymer solution at pH 3.2 was more complex than that at pH 5.0, at which pseudoplasticity only was observed for solutions of all copolymers. Contact angles of copolymer solutions on a glass sheet were measured. The data indicated that contact angles of hydrocarbon-modified polymers were smaller than those of fluorocarbon analogues. As time passed the contact angle became smaller and smaller. Fluorocarbon analogues were better than hydrocarbon analogues, and longer hydrophobic chains were better than shorter chains, at maintaining the hydrophobic character of the surface.     

Mixed micellar phases of nonmiscible surfactants: mesoporous silica with bimodal pore size distribution via the nanocasting process

Highly organized mesoporous silica monoliths were reproducibly prepared by nanocasting mixtures of fluorinated nonionic surfactants and micelles of two hydrocarbon block copolymers. It is the special feature of this fluorocarbon/hydrocarbon template mixture that they form not mixed micelles but individual micelles instead. By careful analysis of the pore architectures by gas sorption measurements and transmission electron microscopy in dependence on the relative template concentration, two different situations could be identified: (a) mesoscopically demixed samples and (b) mixed micellar phases where the two different micelles are packed in some type of organized alloy phase. Besides identification of such mixed phases for the first time for fluorocarbon/hydrocarbon mixtures, the resulting porous systems with controlled bimodal pore size distribution might be interesting from a materials perspective.     

A fluorine-containing hydrophobically associating polymer. I. Synthesis and solution properties of copolymers of acrylamide and fluorine-containing acrylates or methacrylates

Fluorine-containing hydrophobically associating polymers have been synthesized by copolymerization of acrylamide with a small amount of an acrylate or methacrylate having a fluorocarbon containing ester group. It was found that hydrophobic associations occurring between these fluorocarbon chains was stronger than the interactions of the corresponding hydrocarbon comonomers and depend on the length of the fluorocarbon chain. The rheological properties of the copolymer solutions were studied. The solutions were found to be highly pseudoplastic but the viscosity loss was completely reversible upon removal of shear. Evidence for hydrophobic association of the fluorocarbon groups was obtained by the dependence of the Brookfield viscosity on temperature, the addition of NaCl, and the addition of organic solvents, urea, and surfactants.     

粘度法研究疏水改性聚丙烯酸与Np7.5的相互作用

研究了氟基团改性和氟碳、碳氢基团同时改性的聚丙烯酸（HM－PAA）以及参与聚合物（PAA）与非离子表面活性剂Np7.5分别在稀溶液和亚浓溶液下的相互作用对特性粘数和Brookfield表观粘度的影响。结果表明,PAA与Np7.5无明显作用,而M－PAA在Np7.5达到一定浓度后,由于Np7.5参与了疏水缔合,特性粘数和表观粘度发生了明显变化。稀溶液中,氟碳基团较多的聚合物出现了链构象的伸展。亚浓溶液中,疏水改性聚合物的粘度都有先上升后下降的变化,但氟碳含量较多的变化更强烈。     

A novel lyotropic liquid crystal formed by triphilic star-polyphiles: hydrophilic/oleophilic/fluorophilic rods arranged in a 12.6.4. tiling

Triphilic star-polyphiles are short-chain oligomeric molecules with a radial arrangement of hydrophilic, hydrocarbon and fluorocarbon chains linked to a common centre. They form a number of liquid crystalline structures when mixed with water. In this contribution we focus on a hexagonal liquid crystalline mesophase found in star-polyphiles as compared to the corresponding double-chain surfactant to determine whether the hydrocarbon and fluorocarbon chains are in fact demixed in these star-polyphile systems, or whether both hydrocarbon and fluorocarbon chains are miscible, leading to a single hydrophobic domain, making the star-polyphile effectively amphiphilic. We report SANS contrast variation data that are compatible only with the presence of three distinct immiscible domains within this hexagonal mesophase, confirming that these star-polyphile liquid crystals are indeed hydrophilic/oleophilic/fluorophilic 3-phase systems. Quantitative comparison with scattering simulations shows that the experimental data are in very good agreement with an underlying 2D columnar (12.6.4) tiling. As in a conventional amphiphilic hexagonal mesophase, the hexagonally packed water channels (dodecagonal prismatic domains) are embedded in a hydrophobic matrix, but that matrix is split into oleophilic hexagonal prismatic domains and fluorophilic quadrangular prismatic domains.     

Micellization of fluorinated amphiphiles

New cationic fluorinated surfactants and new types of fluorinated surfactants having fluorocarbon–hydrocarbon hybrids, dimeric and polymeric structure have been synthesized recently. Their synthesis requires many steps and consequently requires much time and high expense. Since the fluorinated surfactants have unusual molecular aggregation properties, ¹⁹F-NMR, novel fluorescence probes and cryo-transmission electron microscope techniques have been applied to study their aggregation behaviour in aqueous systems. Their unique characteristics are summarized as follows: (1) the dissolution process from solid state to dissolved aggregate state requires a very long time for the long chain fluorinated surfactants under thermodynamic equilibrium. The equilibration time can be reduced at higher temperatures; (2) interfacial properties and critical micelle concentration (CMC) are influenced by the nature of the hydrophobic terminal groups (CF₃− or HCF₂−); (3) the fluorocarbon functionality can make it possible even for single-chain amphiphiles to form vesicles or lamellar structures; (4) the hybrid surfactant made of both hydrocarbon and fluorocarbon chains showed a life time of 2.0×10⁻³ s for the exchange rate between the monomeric and the micellar states at the CMC and moreover, these detergents can cosolubilize fluorocarbon–hydrocarbon mixed solubilizates.