A small angle neutron scattering study of the sodium di-n-pentyl phosphate micelles in water

Small angle neutron scattering has been used to elucidate the size and shape of a micelle in the sodium di-n-pentyl phosphate (DPP)-water system. The results are summarized as follows. For the DPP micelle, the aggregation number (n) depends on the concentration (n=12, at 7.0 wt% andn=15 at 10.0 wt%). The minimum micelle is spherical and has an aggregation numbern=7. For the DPP-micellar system, it can be assumed that micellar growth and variation from the spherical to probate shape occurs with an increase in concentration above the CMC.     

Mixed spherical and wormlike micelles: a contrast-matching study by small-angle neutron scattering

Small-angle neutron scattering studies were used to investigate the effect of adding an alcohol ethoxylate nonionic surfactant (d-C12E20) to aqueous solutions of a cationic surfactant, erucyl bis(hydroxyethyl) methylammonium chloride (EHAC), with and without salt (KCl). The systematic use of contrast-matching, by alternately highlighting or hiding one of the surfactants, confirms that mixed micelles are formed. In salt-free solutions, mixed spherical micelles are formed and a core-shell model combined with a Hayter-Penfold potential was used to describe the data. The core radius is dominated by the EHAC tails and the outer radius determined by the ethoxylate headgroups of the nonionic surfactant. Addition of KCl promotes micellar growth; however, results of varying the solvent contrast revealed that when the nonionic surfactant is incorporated into the wormlike structure micellar breaking is promoted. Thus, mixed wormlike micelles with shorter contour lengths compared to the pure EHAC worms are formed.     

Highly extended conformation of polyelectrolytes incorporated into hybrid threadlike micelles studied by small angle neutron scattering

SANS measurements revealed that polyelectrolytes, sodium salt of partially sulfonated polystyrenes, incorporated into enormously long hybrid threadlike micelles formed in aqueous solution with a cationic surfactant, cetyltrimethylammonium bromide, have a highly extended conformation with high confinement along the micelles with a radius of 2.3 nm.     

Characteristic lengths and the structure of salt free polyelectrolyte solutions. A small angle neutron scattering study

We have studied salt free semi dilute polyelectrolyte solutions by small angle neutron scattering. Specific labelling associated with an extrapolation method has allowed the separation of the form factor of a single polyelectrolyte chainS ₁(q) and the structure factorS ₂(q). Two lengths are deduced from these two factors: the persistence lengthb _t which characterizes the electrostatic interactions along the chain by a fitting ofS ₁(q) with calculation of the scattering function for a wormlike chain, and fromS ₂(q),q _m ^–1 which characterizes the interactions between chains. These two lengths vary in the same way with the concentration of polyions (b _t C _p ^–1/2 ,q _m ^–1 C _p ^–1/2 ) and a constant relation exists between them: only one length is then necessary to describe the structure of polyelectrolyte soltuion on this semidilute concentration range.Laboratoire Commun CEA-CNRS.     

Structure of casein micelles I. Small angle neutron scattering and light scattering fromβ- andχ-casein

Casein is the main protein component of milk and is of remarkable colloidal stability. Under the influence of milk clotting enzymes casein shows the striking behaviour of coagulation. This clotting process has already been studied by other groups, neglecting the fact that casein is not a homogeneous protein. The purpose of the present study is focused, in this first stage, on the determination of the structure of the various casein components. In cooperation with other laboratories we have been able to obtain the well separated individual proteins. Studies have been performed so far with- and-casein. For detailed structural information we carried out small angle neutron scattering and combined static and dynamic light scattering measurements and determined the molecular weight,M _w, the radius of gyration, S ² the hydrodynamic radius,R _H, the-value and the particle scattering factor, P_z(q). The two caseins show a strikingly different behaviour. For the-casein we found a star-like structure, i. e. an aggregation pattern that is expected for a common micelle. The micelle consists of about 38 monomer chains. The aggregates of-casein appear to be composed of star-like submicelles, where each submicelle contains nine-casein chains and the total degree of aggregation is about 140.     

Mixed micelles of fluorinated and hydrogenated surfactants

The model mixed surfactant system of sodium perfluorooctanoate and sodium decyl sulfate was carefully reexamined by a combination of nuclear magnetic resonance methods. Over a wide range of sample compositions, detailed (19)F and (1)H chemical shift data in combination with self-diffusion coefficients for the perfluorooctanoate and decyl sulfate ions are collected. All data are analyzed together in a framework that uses a minimal number of initial assumptions to extract the monomer concentrations of both surfactants and the micellar chemical shifts of (19)F and (1)H as a function of relative concentration. The main conclusion drawn from this analysis is that there exists neither complete demixing nor complete mixing on molecular or micellar levels. Instead, the experimental data favor a single type of micelles within which fluorinated surfactants are preferentially coordinated by fluorinated ones and hydrogenated surfactants by hydrogenated ones. The data are quantitatively interpreted in the framework of the first approximation of the regular solution theory (also called the quasi-chemical treatment) leading to an energy of mixing of omega = W/kT = 0.98 between the constituting surfactant types. These findings may help to resolve a long controversy about micellar mixing-demixing in this particular mixture and in its relatives.     

Synthesis and comparative behaviour study of fluorocarbon and hydrocarbon cationic surfactants in aqueous media

A series of perfluorinated cationic surfactants and their corresponding hydrocarbon ones whose general formula is C_nX_2n+1-C(O)NH-(CH₂)₃-N⁺Me₃, I⁻, with X = F, H and n = 9, 11, have been synthesized via two steps. Their aggregative and surface-active properties were studied in aqueous solution using tensiometry and conductimetry. The critical micelle concentrations and the molecular areas at the air/water interface of fluorinated surfactants are lower than those of their hydrocarbon homologues. Micellar aggregation numbers and geometric packing parameters have been investigated. The results indicated that fluorocarbon surfactants tend to form lamellar aggregates while the hydrocarbon ones associate into spherical aggregates.     

A small angle neutron scattering study of the interface between solids and oil-continuous emulsions and oil-based microemulsions

We have measured the small angle neutron scattering (SANS) from slurries of powder in contact with surfactant solutions and emulsions to determine the fluid/solid interfacial structure. The slurry solids consisted either of graphite or pyrites particles; and the fluids were hexadecane containing the robust commercial polyisobutylenesuccinamide (PIBSA) surfactant, or a high internal phase emulsion of aqueous ammonium nitrate in hexadecane stabilised by PIBSA. To resolve the interfacial structure for both systems, combinations of deuterated and protonated materials were used.At low concentration in hexadecane, PIBSA forms a complete monolayer on graphite with a footprint per molecule of 103 Å² and a layer thickness of 19 Å. At higher concentrations, the complete monolayer of footprint is 61 Å² and 30 Å thick indicating compression of the PIBSA chain coil structure. Geometric exclusion effects caused by the stacking of the graphite particles also results in an excess of oil for ca. 160 Å above the surfactant monolayer.For pyrites in contact with surfactant in hexadecane, the oxidised surface layer, while smooth at the oil interface, is diffuse and/or rough at the interface with the bulk sulphide below. There is again a complete monolayer of surfactant adsorbed at the oxide surface, in a relatively compressed state with a footprint of 70 Å², more tightly bound than on graphite. The excess of oil phase above the adsorbed surfactant monolayer is observed for samples with larger pyrites particle sizes but not for a sample with smaller particles. This suggests that the oil excess does arise from purely geometric solid particle packing, but that the local particle surface curvatures are significantly higher than the overall particle size would suggest.The scattering from the pyrites/emulsion interface was modelled by a 30 Å thick monolayer of surfactant coating an oxide surface with a molecular footprint of 123 Å². For the larger particle size samples, there is a 30 Å thick layer of oil above the pyrites particle surface before a bulk emulsion/pyrites mixture is reached.These results extend previous reflectometry experiments on the silicon/emulsion interface, indicating that for stable emulsions the structures are qualitatively similar for three dissimilar solid surfaces. They show that useful results on surfactant structure and emulsion layering at the solid/emulsion and other solid/fluid interfaces can be simply obtained by SANS on powder samples variously contrasted by deuteration. SANS can be applied to a much greater range of solid interfaces than reflectometry since large neutron-transparent single crystals are not required, although the variety of faces in a powdered material degrades the quality of the information.     

Trifluoperazine effects on anionic and zwitterionic micelles: a study by small angle X-ray scattering

In this work small angle X-ray scattering (SAXS) studies on the interaction of the phenothiazine trifluoperazine (TFP, 2-10 mM), a cationic drug, with micelles of the zwitterionic surfactant 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS, 30 mM) and the anionic surfactant sodium dodecyl sulfate (SDS, 40 mM) at pH 4.0, 7.0, and 9.0 are reported. The data were analyzed through the modeling of the micellar form factor and interference function, as well as by means of the distance distribution function p(r). For anionic micelles (SDS), the results evidence a micellar shape transformation from prolate ellipsoid to cylinder accompanied by micellar growth and surface charge screening as the molar ratio TFP:SDS increases in the complex for all values of pH. Small ellipsoids with axial ratio nu=1.5+/-0.1 (long dimension of 60 A) grow and reassemble into cylinder-like aggregates upon 5 mM drug incorporation (1 TFP:8 SDS monomers) with a decrease of the micelle surface charge. At 10 mM TFP:40 mM SDS cylindrical micelles are totally screened with an axial ratio nu approximately 4 (long dimension approximately 140 A at pH 7.0 and 9.0). However, at pH 4.0, where the drug is partially diprotonated, 10 mM TFP incorporation gives rise to a huge increase in micellar size, resulting in micelles at least 400 A long, without altering the intramicellar core. For zwitterionic micelles (HPS), the results have shown that the aggregates also resemble small prolate ellipsoids with averaged axial ratio approximately nu=1.6+/-0.1. Under TFP addition, both the paraffinic radius and the micellar size show a slight decrease, giving evidence that the micellar hydrophobic core may be affected by phenothiazine incorporation rather than that observed for the SDS/TFP comicelle. Therefore, our results demonstrate that the axial ratio and shape evolution of the surfactant:TFP complex are both dependent on surfactant surface-charge and drug:surfactant molar ratio. The results are compared with those recently obtained for another phenothiazine drug, chlorpromazine (CPZ), in SDS and HPS micelles (Caetano, Gelamo, Tabak, and Itri, J. Colloid Interface Science 248 (2002) 149).     

Geometrical shape of micelles formed by cationic dimeric surfactants determined with small-angle neutron scattering

The influence of spacer group on the geometrical shape of micelles formed by quaternary-bis dimeric (Gemini) surfactants C(12)H(25)N(CH(3))(2)(CH(2))(s)N(CH(3))(2)C(12)H(25) (12-s-12) has been investigated with small-angle neutron scattering (SANS). Dimeric surfactants with a short spacer unit (12-3-12 and 12-4-12) are observed to form elongated general ellipsoidal micelles with half axes a < b < c, whereas SANS data demonstrate that 12-s-12 surfactants with 6 ≤ s ≤ 12 form rather small spheroidal micelles rather than strictly spherical micelles. By means of comparing our present SANS results with previously determined growth rates using time-resolved fluorescence quenching, we are able to conclude that micelles formed by 12-6-12, 12-8-12, 12-10-12, and 12-12-12 are shaped as oblate rather than prolate spheroids. As a result, our present investigation suggests a never before reported structural behavior of Gemini surfactant micelles, according to which micelles transform from elongated ellipsoids to nonelongated oblate spheroids as the length of the spacer group is increased. The aggregation number of oblate micelles is observed to monotonously decrease with an increasing length of the surfactant spacer group, mainly as a result of a decreasing minor half axis (a), whereas the major half axis (b) is rather constant with respect to s. We argue that geometrically heterogeneous elongated micelles are formed by dimeric surfactants with a short spacer group mainly as a result of the surface charges becoming less uniformly distributed over the micelle interface. As the length of the spacer group increases, the distance between intramolecular charges become approximately equal to the average distance between charges on the micelle interface, and as a result, rather small oblate spheroidal micelles with a more uniform distribution of surface charges are formed by dimeric 12-s-12 surfactants with 6 ≤ s ≤ 12.     

Small angle neutron scattering study of tetramethylurea solutions

The results of small-angle neutron scattering(SANS) carried out on aqueous and CS₂ solutions of tetramethylurea(TMU) are compared. It is shown that the SANS data indicate the formation of TMU-TMU dimers in both solutions.     

Small angle neutron scattering study of polyelectrolyte conformation incorporated into hybrid threadlike micelles under strong shear flows

A small angle neutron scattering study revealed that polyelectrolytes, sodium salts of partially sulfonated polystyrenes with narrow distributed molar masses of Mn = 27 x 10(3) and 340 x 10(3), which were incorporated into hybrid threadlike micelles formed with cetyltrimethylammonium bromide in aqueous (deuterium oxide) solutions at a quiescent state, behaved as rigid rods with lengths of 16 and 200 nm and the same radius of 2.3 approximately 2.4 nm, respectively. Under strong shear flows at shear rates much higher than the reciprocal of the mechanical relaxation time for the solution, the formed hybrid threadlike micelles were highly orientated to the shear flow axis owing to the generation of a shear induced liquid crystalline phase. The polyelectrolytes incorporated into the highly orientated micelle also maintained essentially the same conformation as those in the randomly orientated micelles in a quiescent state even at high shear rates.     

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。     

Spreading of mixed solution of fluorocarbon and hydrocarbon surfactants on oil

Colloid and Polymer Science - The surface tension and the spreading (on oil) properties of the mixed solution of anionic (or cationic) and cationic (or anionic) fluorocarbon and hydrocarbon...     

Effect of heat treatment on pore structure in nano-crystalline NiO: A small angle neutron scattering study

Nano-crystalline nickel oxide powder was synthesized by a precipitation route. Powder samples were heat treated at 300, 600 and 900 °C, and pore structure evolution was followed by small angle neutron scattering (SANS) technique. SANS measurements were carried out also on pelleted samples in order to study the modifications of pore morphology due to heat treatment. SANS data reveal scattering from pores at two different length scales. The pore structure at various heat treatment temperatures does not follow any scaling behavior.     

Structure and dynamics of water in nonionic reverse micelles: A combined time-resolved infrared and small angle x-ray scattering study

We study the structure and reorientation dynamics of nanometer-sized water droplets inside nonionic reverse micelles (water/Igepal-CO-520/cyclohexane) with time-resolved mid-infrared pump-probe spectroscopy and small angle x-ray scattering. In the time-resolved experiments, we probe the vibrational and orientational dynamics of the O-D bonds of dilute HDO:H(2)O mixtures in Igepal reverse micelles as a function of temperature and micelle size. We find that even small micelles contain a large fraction of water that reorients at the same rate as water in the bulk, which indicates that the polyethylene oxide chains of the surfactant do not penetrate into the water volume. We also observe that the confinement affects the reorientation dynamics of only the first hydration layer. From the temperature dependent surface-water dynamics, we estimate an activation enthalpy for reorientation of 45 ± 9 kJ mol(-1) (11?±?2 kcal mol(-1)), which is close to the activation energy of the reorientation of water molecules in ice.     

Characterization of star polymers in solution by small angle neutron scattering

In this paper we present the small angle neutron scattering characterization of two polyisoprene and one poly(ethylenepropylene) star polymers in solution. In the limit of low scattering vector, Q, and low concentration, φ, the molecular characteristics were determined. The molecular weights obtained are in good agreement with light scattering data. Deviations in second virial coefficients are due to a difference in solvent quality. Radii of gyration of the stars are well determined by the use of Kratky plots as is shown by the good agreement with average values of Zimm and Guinier analysis. Additionally, some thermodynamic properties were investigated in dilute and semidilute solutions. We have found that the concentration dependence of the osmotic compressibility is influenced by an expected step at the overlap concentration in both concentration regions.     

Segregation of two amphiphilic molecules within nonspherical micelles: A neutron scattering study

The internal structure of the disk-like aggregate of a lyotropic nematic phase formed by two amphiphiles, potassium laurate and decanol, in the presence of water was studied by neutron scattering with contrast variation method. These experiments show that the two amphiphiles are not distributed uniformly in the aggregate. The potassium laurate concentration is higher in the rim of the disk, where the interface exhibits a semitoroidal curvature, than in its central core, where the curvature is lower. This segregation of the two amphiphiles within the aggregate may be invoked to explain the existence of finite bilayered aggregates which had been suggested to be unstable relative to infinite bilayers by previous models.     

Investigation of heterogeneities in solid polyethylene by small angle neutron scattering

Small angle neutron scattering was applied to the investigation of heterogeneities in solid poly-ethylene. The heterogeneities arise from the contrast between amorphous and crystalline regions and also from the presence of a small fraction of voids. The method is easily put on an absolute basis by calibration with an incoherent scatterer, in this case, cyclohexane.