Structure and rheological properties of model microemulsion networks filled with nanoparticles

Model microemulsion networks of oil droplets stabilized by non-ionic surfactant and telechelic polymer C18 -PEO(10k)- C18 have been studied for two droplet-to-polymer size ratios. The rheological properties of the networks have been measured as a function of network connectivity and can be described in terms of simple percolation laws. The network structure has been characterised by Small Angle Neutron Scattering (SANS). A Reverse Monte Carlo (RMC) approach is used to demonstrate the interplay of attraction and repulsion induced by the copolymer. These model networks are then used as matrix for the incorporation of silica nanoparticles (R = 10 nm), individual dispersion being checked by scattering. A strong impact on the rheological properties is found for silica volume fractions up to 9%. q(A-1).     

Development and prospects of Very Small Angle Neutron Scattering(VSANS) techniques

Very Small Angle Neutron Scattering(VSANS) is an upgrade of the traditional Small Angle Neutron Scattering(SANS) technique which can cover three orders of magnitude of length scale from one nanometer to one micrometer. It is a powerful tool for structure calibration in polymer science, biology, material science and condensed matter physics. Since the first VSANS instrument, D11 in Grenoble, was built in 1972, new collimation techniques,focusing optics(multi-beam converging apertures, material or magnetic lenses, and focusing mirrors) and higher resolution detectors combined with the long flight paths and long incident neutron wavelengths have been developed.In this paper, a detailed review is given of the development, principles and application conditions of various VSANS techniques. Then, beam current gain factors are calculated to evaluate those techniques. A VSANS design for the China Spallation Neutron Source(CSNS) is thereby presented.     

Study of tetrabutylammonium bromide in aqueous solution by neutron scattering

The study of electrolyte solutions by neutron scattering is an example of the large range of possibilities of the technique. Structure and dynamics at different time and length scales, discrimination of global from local motions, separation of coherent from incoherent contributions are necessary to embrace the complexity of a subject where charge and hydrophobicity play important and competitive roles. The behaviour of aqueous solutions of tetrabutylammonium bromide is studied here by several neutron scattering techniques: Small Angle Neutron Scattering, Neutron Diffraction, Time-of-Flight and Neutron Spin Echo. We concentrate on the conformation and dynamics of the hydrophobic cations. In particular, the center-of-mass (CoM) motion of the cation at the microscopic scale is best described via the low Q coherent signal, as measured by Neutron Spin Echo. Due to a possible cage formation effect in the TBABr solution, at the scale of the distance between cations, the cationic CoM relaxation time is larger than that predicted by a simple extrapolation of results issued from the hydrodynamic regime and those obtained from the incoherent signal analysis.     

Probing simultaneously the volume and surface structure of nanospheres adsorbed at a solid-liquid interface by GISANS

We demonstrate in this paper the possibilities offered by Grazing Incidence Small Angle Neutron Scattering (GISANS) for the study of solid/liquid interfaces. We present experimental results obtained by Specular Neutron Reflectivity (SNR) and GISANS on a model system made of silica nanospheres adsorbed on a silicon wafer by electrostatic interactions both at solid/air interface and solid/liquid interfaces. At the solid/liquid interface, we demonstrate that grazing incidence scattering enables to discriminate the surface and the bulk scattering. The surface structure factor derived from GISANS shows that the nanospheres are organized as a repulsive liquid system, with a surface fraction occupation consistent with values obtained by SNR. This original setup highlights a direct correlation between the structure of the silica nanospheres in solution and their organization on the surface: due to the strong electrostatic repulsions between spheres, their organization at the surface is close to the projection in 2D of the 3D organization of the nanospheres in solution.     

Time-of-flight grazing incidence small angle neutron scattering on Gd nanowires

A Gd nanowire grating with a periodicity of approximately 225 nm prepared on a faceted substrate was investigated by Time-Of-Flight Grazing Incidence Small Angle Neutron Scattering. These measurements allowed to obtain information on the critical wavelength, the reflected and transmitted intensities and also allowed a reconstruction of large portions of the grating truncation rods in reciprocal space. Results were obtained for various orientations around the sample normal and compared with a theoretical model, showing good agreement.     

Macroscopic and microscopic structural integrity in magnetic colloids—cationic micellar solution: Rheology, SANS and magneto-optical study

A stable mixture of two colloid system composed of double surfactant coated aqueous nanomagnetic fluid and aqueous micellar solution of cationic micelles of cetyletrymethyl ammonium bromide (CTABr) is prepared as a function of nanomagnetic fluid concentration. This mixed system is analyzed using three techniques such as zero field and field induced viscosity measurements, Small Angle Neutron Scattering technique and magneto-optical birefringence measurements. In field induced viscosity measurement it is observed that even 20% magnetic fluid concentration in CTABr aqueous solution shows 75% increase in viscosity compared to pure magnetic fluid. This suggests that in presence of CTABr micelles, a novel magneto rheological effect for low concentration of magnetic fluid is observed. From SANS measurements it is observed that aggregation number and a/b ratio increases with magnetic fluid concentration and magnetic birefringence reveals non-superimpose behavior of normalized field induced retardation. Results of these experiments are compared and indicate zero fields and field induced structural integrity between magnetic particles and soft micelles.     

Internal structure of magnetic endosomes

The internal structure of biological vesicles filled with magnetic nanoparticles is investigated using the following complementary analyses: electronic transmission microscopy, dynamic probing by magneto-optical birefringence and structural probing by Small Angle Neutron Scattering (SANS). These magnetic vesicles are magnetic endosomes obtained via a non-specific interaction between cells and anionic magnetic iron oxide nanoparticles. Thanks to a magnetic purification process, they are probed at two different stages of their formation within HeLa cells: (i) adsorption of nanoparticles onto the cellular membrane and (ii) their subsequent internalisation within endosomes. Differences in the microenvironment of the magnetic nanoparticles at those two different stages are highlighted here. The dynamics of magnetic nanoparticles adsorbed onto cellular membranes and confined within endosomes is respectively 3 and 5 orders of magnitude slower than for isolated magnetic nanoparticles in aqueous media. Interestingly, SANS experiments show that magnetic endosomes have an internal structure close to decorated vesicles, with magnetic nanoparticles locally decorating the endosome membrane, inside their inner-sphere. These results, important for future biomedical applications, suggest that multiple fusions of decorated vesicles are the biological processes underlying the endocytosis of that kind of nanometric materials.     

Radiation induced synthesis of silver nanoshells formed onto organic micelles

Synthesis of metal nanoshells around organic micelles is achieved through radiolysis of aqueous solutions of surfactant self-assembled in spherical micelles and metal ions. The formation of the metal nanoshells is evidenced by UV-visible spectroscopy and Small Angle X-ray Scattering.     

Asphaltene multilayer growth in porous medium probed by SANS

Presence of suspended particles such as asphaltene in crude oils could significantly affect the production by means of deposition in porous media especially near the well bore. We investigate this phenomenon using the ability of Small Angle Neutron Scattering technique to probe directly the asphaltene adsorption process in a porous medium at the nanometer length scale under flow conditions. A device based on a quartz tube filled with SiC particles constitute the porous medium in which an asphaltene solution in a mixture of good (toluene)/bad (heptane) solvent is injected under controlled flow. The contrast matching technique enables to match the porous medium scattering contributions and to measure the signal of the deposit. Such a device can be used for curves surface measurements on a setup originally designed for bulk studies and permit thus the direct comparison with measurements on flat surfaces (neutron reflectivity) and indirect adsorption measurements (adsorption isotherm). We show here that asphaltene in good solvent leads to a monolayer whereas addition of bad solvent results in a multilayer growth which is consistent with the deposition behaviour described in the literature.     

In situ SAXS studies of the formation of sodium jarosite

This paper reports the results of time‐resolved synchrotron small‐angle scattering and powder diffraction experiments where natrojarosites were synthesized in situ in order to observe the species produced at the earliest stages of nucleation. The sample temperatures were 333, 353 and 368 K. These compounds were synthesized by co‐precipitation from solution on the Small and Wide Angle Scattering and Powder Diffraction beamlines at the Australian Synchrotron. Scattering data were collected continuously throughout the syntheses. The results presented here show that the first particles to form in solution appear to be amorphous and nucleate on the walls of the reaction vessel. Crucially, there is a single nucleation event which forms particles with an elliptical disc morphology which then grow uniformly before natrojarosite crystallization is observed in complementary powder diffraction data. This nucleation event may represent the key to controlling the growth of jarosites in industrial and environmental settings.     

Dynamic viscoelastic properties of silica alkoxide during the sol-gel transition

The viscoelastic properties of silica alkoxide gel during the sol-gel transition (SGT) are analysed using an extended shear relaxation modulus expression with a functional form based on a product of power law and Debye-Maxwell relaxation kernels. The dynamic properties are probed by small-amplitude oscillatory shear measurements in three viscoelastic domains (pre-SGT, SGT, post-SGT). Using analytical expressions for the storage and loss moduli in these three domains, it is shown that the divergence of the mean characteristic relaxation time in the pre-SGT domain can be successfully described by a percolation with bond fluctuation dynamics. It is also shown that the equilibrium shear modulus in the post-SGT domain can be successfully described by a percolation model based on an analogy with an electrical network. The amplitude and the critical exponent of the power law relaxation at the gelation time first introduced by Winter and Chambon are estimated in the pre- and post-SGT domains.Received: 22 July 2003, Published online: 11 November 2003PACS: 83.85.Vb Small amplitude oscillatory shear (dynamic mechanical analysis) - 83.85.St Stress relaxation - 83.60.Bc Linear viscoelasticity - 82.70.Gg Gels and sols     

用光散射研究部分相容聚合物共混物的相间过渡层(英文)

在光散射的理论中 ,密度均方起伏η2在两相完全不相容的体系中 (界面间也不存在相互粘附 )η2 =Φ1Φ2 (α1-α2 )。对于界面间有相互作用或形成一定的相容区时 ,η2将变小 ,则有η2 =(α2 -α1) 2 (φ1φ2 -φ3/6)。α1、α2 为两组元分别的极化率 ,φ1、φ2 为两组元的体积分数。本文根据部分相容的聚合物共混体系中的分散相尺寸γ和积分不变量θ,可计算出φ3,并提出相间弥散层的概念 ,进而计算出弥散层的厚度 d,从而发展了光散射理论。激光小角散射计算的弥散层厚度 d与 X光小角散射计算的界面层厚度σb是相对应的。在计算中应用相关距离 ac代替分散性尺寸γ是可行的 (也可用均方旋转半径 R2g代替 )。文中给出了 PA6/PP合金的弥散层厚度 d和界面层厚度σb的计算结果 ,同时给出了 HIPS/Pc BR合金在熔体动态过程中两相间弥散层厚度的变化     

用小角X射线散射法和31P核磁共振技术研究蓖麻酸对磷脂胆固醇混合脂质体液晶态结构的影响

采用小角X射线散射法和³¹P核磁共振技术研究了蓖麻酸对磷脂酰乙醇胺和胆固醇混合脂质体液晶态结构的影响,实验结果表明:蓖麻酸对磷脂胆固醇混合脂质体结构有稳定作用。在含有高效分散剂的磷酸盐缓冲溶液中制成的液晶态蓖麻酸多相脂质体由立方六角相构成。 关键词：     

Scientific Review: Interactions of PEO with Monovalent Electrolytes in Solvents of Different Hydrogen Bonding Capacities

Small-Angle Neutron Scattering (SANS) has been used in order to investigate the ion binding capacities of PEO in different solvents. Aprotic (acetonitrile) as well as protic (methanol and water) solvents, have been studied where methanol and water form an average two and four tetrahedrally oriented hydrogen bonds per molecule, respectively [1]. Unusual behavior of PEO has been observed in aprotic solvents and solvents with moderate hydrogen bonding where monovalent ions associate to the polymer backbone leading to a polyelectrolyte-like (where a certain fraction of monomers are charged) behavior. This is in marked contrast to behavior in aqueous solutions where water molecules associate via hydrogen bonding to the polymer and the ions are more preferentially coordinated by the solvent than the polymer.     

中国散裂中子源小角中子散射谱仪探测器研制

中子小角散射探测器是小角散射（SANS）谱仪的关键设备之一,探测器要求有足够大的探测面积、较高的探测效率及较好的空间分辨率,能够在真空腔中稳定地工作并可在腔体内前后移动。综合考虑,SANS探测器采用120只8 mm直径位置灵敏3He管,组成有效面积1 000 mm（X）×1 020 mm（Y）的二维探测器阵列。探测器阵列分为10个模块,每一个模块功能完全独立,包括12只3He管及其对应的读出电子学和数据获取系统。读出电子学位于探测器背面的回字形密闭腔体内,由CSNS电子学组自主研发。SANS探测器从设计、选型、样机、调试到安装历时三年,中子束流实验结果显示探测器探测效率大于50%（@2Å）,空间分辨率好于10 mm（FWHM）,完全达到设计要求,目前正在中国散裂中子源小角散射谱仪运行使用。     

Characterization of mixed micelles of sodium cumene sulfonate with sodium dodecyl sulfate and cetyl trimethylammonium bromide by SANS,FTIR spectroscopy and NMR spectroscopy

The aqueous solutions of sodium cumene sulfonate (NaCS) and its mixtures with cetyl trimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) are studied by Small Angle Neutron Scattering (SANS), Fourier Transform Infrared (FTIR) spectroscopy and Nuclear Magnetic Resonance (NMR) spectroscopy. The compositions of mixed micelles are determined using Rubingh's Regular Solution Theory. NaCS when added to CTAB solution leads to the formation of long rod shaped micelles with dramatic increase in the CTAB aggregation number. Its addition to SDS on the other hand results in the formation of smaller mixed micelles where parts of SDS molecules in the micelle are replaced by NaCS molecules. NaCS–SDS mixed micelles prefer elongated ellipsoidal geometry in order to accommodate short NaCS molecules. The FTIR spectroscopy results indicate enhanced ordering of CTAB tails inside the NaCS–CTAB mixed micelles with reduction in the gauche/trans conformer ratio. Addition of NaCS to SDS on the other hand results in decreased ordering of SDS tails, as compared to SDS micelles alone. The chemical shifts observed in ¹H NMR spectra of NaCS–SDS and NaCS–CTAB mixture indicate that NaCS resides near the surface of the SDS micelle.     

Neutrons for fuel cell membranes: Structure, sorption and transport properties

A molecular level understanding of structure and transport properties in fuel cell ionomer membranes is essential for designing new electrolytes with improved performance. Scattering techniques are suited tools for this purpose. In particular, neutron scattering, which has been extensively used in hydrogen-containing systems, is well adapted to investigate water-dependent complex polymeric morphologies. We report Small-Angle Neutron Scattering (SANS) studies on different types of fuel cell polymers: perfluorinated, radiation-grafted and sulfonated polyphosphazene membranes. We show that contrast variation methods can be efficiently employed to provide new insights on membrane microstructure and reveal ionic condensation effects. Neutrons have been used also as non-intrusive diagnosis tool to probe water properties and distribution inside membranes. Recently, in-situ neutronography and SANS experiments on operating fuel cells have been reported. In-plane cartography of water distribution at the surface of bipolar plates and water profiles across membrane thickness have been obtained and studied as a function of operating conditions. The last section of the article is devoted to the use of Quasi-Elastic Neutron Scattering to study water dynamics at molecular scale. We show that analysis with an appropriate sophisticated diffusion model allows to extract diffusion coefficients, characteristic times and length-scales of molecular motions. This quantitative information is fruitfully integrated in multi-scale modelling and usefully compared with numerical simulations. QENS also permits to compare alternative polymers and relate dynamical properties to chemical composition and membrane nanostructure.     

2011 U.S. National School on Neutron and X-ray Scattering

The 13^th annual U.S. National School on Neutron and X-ray Scattering was held June 11-25, 2011, at both Oak Ridge and Argonne National Laboratories. This school brought together 65 early career graduate students from 56 different universities in the United States and provided them with a broad introduction to the properties and techniques available at the major large-scale neutron and synchrotron X-ray facilities. This school is focused primarily on techniques relevant to the physical sciences, but also touches on cross-disciplinary bio-related scattering measurements. During the school, the students received lectures by more than 30 researchers from academia, industry, and national laboratories and participated in a number of short demonstration experiments at Argonne's Advanced Photon Source (APS) and Oak Ridge's Spallation Neutron Source (SNS) and High Flux Isotope Reactor (HFIR) facilities to get hands-on experience in using neutron and synchrotron sources.     

Quantitative analysis of lyotropic lamellar phases SANS patterns in powder oriented samples

We have developed a detailed numerical method based on the Caillé model to fit Small Angle Neutron Scattering profiles of powder-oriented lyotropic lamellar phases. We thus obtain quantitative values for the Caillé parameter and the smectic penetration length from which we can derive the smectic compression modulus and the membrane mean bending modulus. Our method, applied to a surfactant lamellar phase system decorated by amphiphilic copolymers, provides excellent fits for any intermembrane spacing or membrane concentration over the entire q-range of the SANS experiments. We compare our fits with those obtained from the model of Nallet et al. (J. Phys. II 3, 487 (1993)), which is reviewed. Good fits are obtained with both methods for samples exhibiting “hard” smectic order (sharp Bragg peak, moderate small angle scattering). Only our procedure, however, gives good fits in the case of “soft” smectic order (smooth Bragg peak, strong small angle scattering). A quantitative criterion to discriminate between these “soft” and “hard” samples is also proposed, based on a simple analogy with smectic-A liquid crystal in contact with an undulating solid surface. This allows us to anticipate the type of thermodynamic information that can be derived from the fits.     

Mechanical shear can accelerate the gelation of actin filament networks

Rearrangements of the filamentous actin cytoskeleton at the leading edge of motile cells occur under large mechanical stresses. Contrary to conventional wisdom, we show that mechanical deformations applied during gelation can accelerate the rate of gelation and produce F-actin networks that are stiffer and mechanically more resilient than those polymerized under low or high shear deformations. Above a threshold shear strain amplitude, F-actin networks collapse and become soft and liquidlike. This effect of shear-induced strengthening of polymerizing networks depends on the state of hydrolysis of the actin-bound adenosine triphosphate.