Discovery of surfactants for metal/semiconductor separation of single-wall carbon nanotubes via high-throughput screening

We report novel surfactants that can be used for the separation of metallic (M) and semiconducting (S) single-wall carbon nanotubes (SWCNTs). Among the M/S separation methods using surfactants in an aqueous solution, sodium dodecyl sulfate plays a key role in density gradient ultracentrifugation (DGU) and agarose gel separations. In this study, we screened 100 surfactants for M/S separation using a high-throughput screening system. We identified five surfactants, which could be used for both DGU and agarose gel separations, suggesting that the basic principle of these separations is common. These surfactants have relatively low dispersibilities, which is likely due to their common structural features, i.e., straight alkyl tails and charged head groups, and appeared to enable M- and S-SWCNTs to be distinguished and separated. These surfactants should stimulate research in this field and extend the application of electrically homogeneous SWCNTs not only for electronics but also for biology and medicine.     

Photoinduced electron transfer in a protein-surfactant complex: probing the interaction of SDS with BSA

Photoinduced fluorescence quenching electron transfer from N,N-dimethyl aniline to different 7-amino coumarin dyes has been investigated in sodium dodecyl sulfate (SDS) micelles and in bovine serum albumin (BSA)-SDS protein-surfactant complexes using steady state and picosecond time resolved fluorescence spectroscopy. The electron transfer rate has been found to be slower in BSA-SDS protein-surfactant complexes compared to that in SDS micelles. This observation has been explained with the help of the "necklace-and-bead" structure formed by the protein-surfactant complex due to coiling of protein molecules around the micelles. In the correlation of free energy change to the fluorescence quenching electron transfer rate, we have observed that coumarin 151 deviates from the normal Marcus region, showing retardation in the electron transfer rate at higher negative free energy region. We endeavored to establish that the retardation in the fluorescence quenching electron transfer rate for coumarin 151 at higher free energy region is a result of slower rotational relaxation and slower translational diffusion of coumarin 151 (C-151) compared to its analogues coumarin 152 and coumarin 481 in micelles and in protein-surfactant complexes. The slower rotational relaxation and translational diffusion of C-151 are supposed to be arising from the different location of coumarin 151 compared to coumarin 152 and coumarin 481.     

Determination of homologues anion surfactants in technical preparations using a multisensor system and HPLC

New potentiometric solid-contact sensors with polyvinyl chloride membranes based on compounds of alkyl sulfates with cationic complexes copper(II)–organic reagent are proposed for the determination of synthetic anionic surfactants (ASs). Multisensor systems are developed for the quantitative determination of ASs in raw technical preparations (alkylbenzene sulfonates, alkyl sulfates, and sodium cocosulfate).     

Micellization in aqueous solutions of mixed surfactants containing alkylpolyglucosides

Tensometry is used to find the dependences of critical micelle concentration in aqueous solutions on the composition of mixed systems comprising anionic surfactants (alkyl sulfates and individual sodium soaps) and alkylpolyglucosides. Mixed micellization is revealed and the compositions of micelles and the parameters of intermolecular interaction are calculated. The average hydrodynamic diameter of micelles is measured by dynamic light scattering.     

Surface and aggregation behavior of aqueous solutions of Ru(II) metallosurfactants: 4. Effect of chain number and orientation on the aggregation of [Ru(bipy)2(bipy')]Cl2 complexes

The structure of aggregates formed by eight surfactant [Ru(bipy)2(p,p'-dialkyl-2,2'-bipy)]Cl2 complexes-which we express as Ru(p)(q)Cn, where n (=12 or 19) is the alkyl chain length, p (=4 or 5) refers to the substitution position on the bipyridine ligand, and q (=1 or 2) is the number of substituted alkyl chains-in aqueous solutions has been examined using small-angle neutron scattering for a range of concentrations close to the critical micelle concentration and for several combinations of n, p, and q. A number of general results emerge. The double-chain surfactants possess a smaller headgroup charge but a larger aggregate size than their single-chain analogues. Over the concentration range studied, the micelles of the single-chain surfactants grow as the concentration is increased, whereas for the double-chain systems, the aggregate size remains unchanged. For both single- and double-chain surfactants, an increase in alkyl chain length is accompanied by an expected increase in aggregate size and an increase in average headgroup charge. The aggregates formed in solutions of resolved double-chain complexes are larger than those found in solutions of racemic mixtures. The Ru(4)(1)C12 and Ru(5)(1)C12 systems form aggregates with high water content. Variation of the substitution position for the single-chain surfactants produces dramatic changes in the structure of the micelles. The aggregates formed in solutions of Ru(4)(1)C19 and Ru(5)(1)C19 display particularly different structures. The Ru(4)(1)C19 system forms essentially spherical aggregates. In contrast, in the Ru(5)(1)C19 system, wormlike aggregates are formed in which the rigid rodlike sections appear to undergo a transition from a noninterdigitated to an interdigitated structure as the concentration is increased. For double-chain surfactants, the aggregation number for p = 4 surfactants is considerably larger than that for p = 5 surfactants.     

Enantiomer separation of drugs by micellar electrokinetic chromatography using chiral surfactants

A review surveying enantiomer separations by micellar electrokinetic chromatography (MEKC) using chiral surfactants is described. MEKC is one of the most popular techniques in capillary electrophoresis, where neutral compounds can be analyzed as well as charged ones, and the use of chiral micelles enable one to achieve the enantioseparation. The chiral MEKC systems are briefly reviewed according to the types of chiral surfactants along with typical applications. As chiral micelles or pseudostationary phases in MEKC, various natural and synthetic chiral surfactants are used, including several low-molecular-mass surfactants and polymerized surfactants or high-molecular-mass surfactants. Cyclodextrin modified MEKC using chiral micelles is also considered.     

Thermodynamic characterization of the interaction behavior of a hydrophobically modified polyelectrolyte and oppositely charged surfactants in aqueous solution: effect of surfactant alkyl chain length

We have used a precision isothermal titration microcalorimeter (ITC) to measure the enthalpy curves for the interaction of a hydrophobically modified polyelectrolyte (D40OCT30) with oppositely charged surfactants (SC(n)S) in aqueous solution. D40OCT30 is a newly synthesized polymer based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-octylammonium chloride groups randomly distributed along the polymer backbone with degree of substitution of 28.1%. The employed anionic surfactants are sodium octyl sulfate (SC(8)S) and sodium tetradecyl sulfate (SC(14)S). Microcalorimetric results along with turbidity and kinematic viscosity measurements demonstrate systematically the thermodynamic characterization of the interaction of D40OCT30/SC(n)S. A three-dimensional diagram with the derived phase boundaries is drawn to describe the effect of the alkyl chain length of surfactant and of the ratio between surfactant and pendant groups on the interaction. A more complete picture of the interaction mechanism for D40OCT30/SC(n)S systems is proposed here.     

Tetrabutylammonium alkyl carboxylate surfactants in aqueous solution: self-association behavior, solution nanostructure, and comparison with tetrabutylammonium alkyl sulfate surfactants

A series of long and ultralong chain tetrabutylammonium alkyl carboxylate (TBACm, TBA = tetrabutylammonium ion; Cm = carboxylate ion C(m-1)H(2)(m-1)CO(2)(-) of total carbon number m) surfactants have been obtained by direct neutralization of the fatty acids with m = 12, 14, 18, 22, and 24 by tetrabutylammonium hydroxide. Time-resolved fluorescence quenching has been used to determine the micelle aggregation number (N) of the surfactants with m = 12, 14, and 18 in the temperature range 10-50 degrees C and of the surfactants with m = 22 and 24 in the temperature range 25-60 degrees C. In all instances the values of N were well below those that can be calculated for the maximum spherical micelle formed by surfactants with the same alkyl chain as the investigated surfactants on the basis of the oil drop model for the micelle core. The microstructure of selected solutions of TBAC22 was examined using transmission electron microscopy at cryogenic temperature and compared to the microstructure of solutions of TBA dodecyl and tetradecyl sulfates. These observations generally confirmed the findings of TRFQ. The self-association behavior of these anionic surfactants with TBA counterions is explained on the basis of the large size and the hydrophobicity of the tetrabutylammonium ions. The important differences in behavior that have been evidenced between tetrabutylammonium alkyl carboxylates and alkyl sulfates are discussed in terms of differences in distribution of the surfactant electrical charge on the headgroup and alkyl chain predicted by quantum chemical calculations (Langmuir 1999, 15, 7546).     

Adsorption of protein-surfactant complexes at the water/oil interface

Interfacial tension measurements have been performed at the water/hexane interface on mixtures of the bovine milk protein β-lactoglobulin and positively charged cationic surfactants (alkytrimethylammonium bromides). The addition of surfactants with different chain lengths leads to the formation of protein-surfactant complexes with different adsorption properties as compared to those of the single protein. In this study, the formation of complexes has been observed clearly for protein-long chain surfactant (TTAB and CTAB) mixtures, which has shown in addition to specific electrostatic interactions the relevance of hydrophobic interactions between surfactant molecules and the protein. The modeling of interfacial tension data by using a mixed adsorption model provides a quantitative understanding of the mixture behavior. Indeed, the value of the adsorption constant of the protein obtained in the presence of surfactants has strongly varied as compared to the single protein. Actually, this parameter which represents the affinity of the molecule for the interface is representative of the hydrophobic character of the compound and so of its surface activity. Even if a more hydrophobic and more surface active protein-surfactant complex has been formed, the replacement of this complex from the interface by surfactants close to their cmc was observed.     

Sphere-to-cylinder transition in hierarchical electrostatic complexes

We report on the formation of colloidal complexes resulting from the electrostatic co-assembly between anionic surfactants and cationic polyelectrolytes or block copolymers. Combining light and X-ray scattering experiments with cryogenic transmission and optical microscopy, we emphasize a feature rarely addressed in the formation of the electrostatic complexes, namely the role of the mixing concentration on the microstructure. At low mixing concentration, electrostatic complexes made from cationic-neutral copolymers and alkyl sulfate surfactants exhibit spherical core-shell microstructures. With increasing concentration, the complexes undergo a sphere-to-cylinder transition, yielding elongated aggregates with diameter 50 nm and length up to several hundreds of nanometers. From the comparison between homo- and diblock polymer phase behaviors, it is suggested that the unidimensional growth is driven by the ability of the surfactant to self-assemble into cylindrical micelles when complexed with cationic polymers.     

QSPR方法预测阴离子表面活性剂亲水亲油平衡值

首次使用量子化学描述符, 建立了两种阴离子表面活性剂亲水亲油平衡(HLB)值的定量结构性质关系模型(QSPR). 最佳模型1包括四类不同结构的烷基硫酸盐和烷基磺酸盐46种阴离子表面活性剂, 复相关系数R²＝1.000. 又建立了包含聚氧乙烯、乙酸、丙酸和碳氟等特殊类型不同结构的73种阴离子表面活性剂的最佳模型2, 复相关系数 R²＝0.993.     

EPR spin probe and spin label studies of some low molecular and polymer micelles

The rotational mobility of spin probes of different shape and size in low molecular and polymer micelles has been studied. Several probes having nitroxide fragment localized either in the vicinity of micelle interface or in the hydrocarbon core have been used. Upon increasing the number of carbon atoms in hydrocarbon chain of detergent from 7 to 13 (sodium alkyl sulfate micelles) or from 12 to 16 (alkyltrimethylammonium bromide micelles) the rotational mobility of spin probes is decreased by the factor 1.5–2.0. The spin probe rotational mobility in polymer micelles (the complexes of alkyltrimethylammonium bromides and polymethacrylic or polyacrylic acids) is less than mobility in free micelles of the same surfactants. The study of EPR-spectra of spin labeled polymethacrylic acid (PMA) indicated that formation of water soluble complexes of polymer and alkyltrimethylammonium bromides in alkaline solutions (pH 9) does not affect the polymer segmental mobility. On the other hand, the polymer complexes formation in slightly acidic water solution (pH 6) breaks down the compact PMA conformation, thus increasing the polymer segmental mobility. Possible structures of polymer micelles are discussed.     

Nanostructures of polyelectrolyte gel–surfactant complexes

Small‐angle X‐ray scattering was used to investigate the nanostructures of complexes formed by slightly crosslinked anionic copolymer gels of poly(sodium methacrylate‐co‐N‐isopropylacrylamide) [P(MAA/NIPAM)] with cetyltrimethylammonium bromide (CTAB), and didodecyldimethylammonium bromide (DDAB), respectively, at room temperature (∼ 23°C). Several highly ordered supramolecular structures were observed in the polyelectrolyte gel–surfactant complexes. In P(MAA/NIPAM)–CTA systems, in sequence with decreasing charge density of the P(MAA/NIPAM) copolymer chains, structures of the Pm3n space group cubic, face‐centered cubic close packing of spheres, and hexagonal close packing of spheres were determined at a charge content of ≥ 75, 67, and 50%, respectively. The spheres and rods in these structures were the spherical and cylindrical micelles formed by the self‐assembly of CTA cations with their paraffin chains inside. Both the aggregation number and the size of the micelles decreased with a decreasing charge density of the copolymer chains. In the P(MAA/NIPAM)–DDA systems, the bilayer lamellar structures formed at charge contents ≥ 75% transferred to bicontinuous cubic structures of the Ia3d space group at charge contents of 50–67%. The rods in the Ia3d cubic structures were formed by the self‐assembly of double‐tailed DDA cations with polar moieties inside. The formation of these highly ordered structures were driven by both electrostatic and hydrophobic interactions of the charged copolymer chains/surfactants and the surfactants/surfactants inside the charged gels. The structures became less ordered by further decreasing the charge content of the P(MAA/NIPAM) chains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2165–2172, 1999     

Surface and micelle properties of novel multi-dentate surfactants

Novel multi-dentate surfactants, based on alkyl amines of varying hydrophobicity were synthesized, and molecular structures were characterized by IR, UV-vis, NMR and FAB-MS. The new surfactants have good water solubility and are highly efficient at reducing aqueous surface tension. Small-angle neutron scattering (SANS) studies were carried out with aqueous solutions in D(2)O to study aggregation. Spherical micelles were shown to form, and these grow with increasing alkyl chain length; their conformation is unusual compared to conventional linear chain surfactants.     

Determination of the surfactant density on SWCNTs by analytical ultracentrifugation

We report on the extensive characterization of single-walled carbon nanotubes (SWCNTs) dispersed in a variety of surfactants, such as sodium dodecyl benzene sulfonate (SDBS), sodium cholate (SC), and three synthesized perylene-based surfactants, by using differential sedimentation in H(2)O and D(2)O. Multidimensional evaluation of the absorption profiles over radius, wavelength, and time allows the determination of the anhydrous specific volumes of the SWCNT-surfactant complexes as well as the concentration of the surfactant reservoir in free micelles with very slow sedimentation coefficients (<1 Svedberg). Among the perylene bisimide surfactants, the smallest derivative is densely adsorbed on the nanotube backbone with an anhydrous specific volume significantly above that of SC or SDBS. Bulky Newkome dendritic groups on one or both ends of the perylene moiety gradually reduce the adsorption density, in accord with the absolute adsorption between 0.66 and 1.7 mmol surfactant per gram SWCNTs. Furthermore, hydrodynamic analysis reveals that SDBS favors the "tails-on" configuration. The distribution of sedimentation coefficients of SWCNTs prepared by high-pressure carbon monoxide decomposition (HiPco) is broader and shifted to faster sedimentation than those prepared by using cobalt-molybdenum catalysis (CoMoCAT), which reflects the polydispersity in diameter and length.     

Separation and characterization of alkyl phenol formaldehyde resins demulsifier by adsorption chromatography, gel permeation chromatography, infrared spectrometry and nuclear magnetic resonance spectroscopy

This paper deals with the separation and characterization of alkyl phenol formaldehyde resins demulsifier by infrared spectrometry and nuclear magnetic resonance spectroscopy after separation of the different surfactants and low molecular additives by adsorption chromatography. Firstly, the types of surfactants are identified by methylene blue chloride-chloroform test method and the elemental analysis such as Ca, K, Mg, Na, P, S and N. Then, the different surfactants and low molecular components are separated by adsorption chromatography after parts of low molecular components are dried in an oven, and the molecular weight distribution is measured by gel permeation chromatography also. Finally, the separated surfactants are determined by Fourier transform infrared (FTIR) spectrometry and nuclear magnetic resonance (NMR) spectroscopy. The distortionless enhancement by polarization transfer (DEPT), H, C correlated spectroscopy (H, C-COSY), H, H correlated spectroscopy (H, H-COSY) and heteronuclear multiple-bond correlation (HMBC) spectroscopy are applied to determine the molecular structures.     

Investigation of the effects of cyclodextrins and organic solvents on the separation of cationic surfactants in capillary electrophoresis

The use of alpha- and beta-cyclodextrin (CD) to understand and to improve the separation of a series of cationic surfactants, homologues of alkylbenzyldimethyl ammonium compounds (ABDACs) with an alkyl chain of varying length (C10-C18), in capillary electrophoresis (CE) is reported for the first time. Similar to the effects of organic solvents, the presence of alpha- or beta-CD in the running buffer was found to reduce peak tailing/loss for the longer-chain ABDACs. Based on fluorescence measurements, it was found that formation of host-guest complexes occurred between alpha- or beta-CD and various ABDACs, with the likelihood that the hydrophobic alkyl chain including into the CD cavity and the positively charged ammonium group remaining outside the cavity. The effects of alpha- or beta-CD can be interpreted in terms of a shift away from the formation of (1) micelles in the buffer system and (2) surfactant aggregates at the fused-silica capillary walls, as a result of the formation of inclusion complexes between alpha- or beta-CD and ABDACs.     

尾链长度高度不对称的阴/阳离子表面活性剂自组织

通过引进新的溶液制备方法,以光散射、流变、电镜等方法研究了烷烃链长度不对称的阴/阳离子表面活性剂等摩尔混合体系,其中阳离子为二十二烷基三甲基溴化铵(C₂₂TABr),阴离子是烷基羧酸钠(C_n-1COONa, n = 4, 6, 8, 10, 12, 14, 16).结果表明,烷烃链长度高度不对称时(C22/n4)生成了球状胶束,随着降低不对称度,聚集体向棒状、蠕虫状直至囊泡转变.在构成囊泡的体系中,随着降低链长不对称度,聚集体尺寸明显增大.机理分析表明,阴/阳离子对的几何形状决定了聚集体的形貌以及它们的转变.     

Morphological characterization of self-assembled peptide nucleic acid amphiphiles

Peptide nucleic acid amphiphiles (PNAA) are a promising set of materials for sequence-specific separation of nucleic acids from complex mixtures. To implement PNAA in micellar separations, the morphology and size of PNAA micelles in the presence and absence of a sodium dodecyl sulfate (SDS) cosurfactant have been studied by small-angle X-ray scattering and dynamic light scattering. We find that a 6-mer PNAA with a 12-carbon n-alkane tail forms ellipsoidal micelles (a = 5.15 nm; b = 3.20 nm) above its critical micelle concentration (CMC) of 110.9 microM. On addition of a stoichiometric amount of complementary DNA, PNAA hybridizes to DNA, suppressing the formation of PNAA micelles. At a ratio of 19:1 SDS/PNAA (total concentration = 20 mM), spherical micelles are formed with outer radius Rs = 2.67 nm, slightly larger than spherical micelles of pure SDS. Capillary electrophoresis studies show that PNAA/DNA duplexes do not comicellize with SDS micelles. No such effects are observed using noncomplementary DNA. The shape and size of the PNAA micelles is also verified by dynamic light scattering (DLS) studies. These results provide an interesting case study with competing electrostatic, hydrophobic, and hydrogen-bonding interactions in micellar systems and make possible the use of PNAA in micellar separations of DNA oligomers.     

Spin probes in micellar and polymer self-associating systems

The results of studies of micellar and self-associating polymer systems by spin probe ESR spectroscopy are summarized. The local dynamics and structures of low-molecular-weight micelles built of cationic surfactants bearing long alkyl chains (from C₁₆ to C₂₂), gels of hydrophobically modified polymers, polymer micelles, micellar complexes of nonionic surfactant (Brij58) with hydrogels based on polyacrylic acid, and associates formed in aqueous solutions of poly(diphenylenesulfophthalide) are discussed. Interest in these systems is caused by prospects of their practical use as carriers in drug delivery, in biotechnology, for the enhancement of oil production, and in other purposes.