Small-angle Neutron Scattering Analysis Research Articles

Morphology and kinetics of nanoheterogeneities in Fe81Ga19–Tb alloy: A small-angle neutron scattering study

The formation of nanoprecipitates in the Fe81Ga19 alloy doped with Tb (∼0.1 at. %) was studied by small-angle neutron scattering (SANS). Measurements at room temperature for several samples pre-aged at a fixed temperature in the range of (300–700)°C revealed a dilute system of precipitates with a characteristic size at nanoscale (<1000 Å) growing with an increase in ageing temperature. In situ measurements during isothermal ageing at 300 °C for 3 h revealed fast (order of 10 min) formation of precipitates. SANS analysis is consistent with the results of neutron diffraction experiments, which suggest the microstructure of this alloy as a matrix of disordered atomic structure (A2 phase) with embedded precipitates of the structurally and magnetically ordered D03 phase.

Scrutinizing micellar transitions and interfacial properties in mixed micelles comprising sodium dodecyl sulfate and sodium oleate: A tensiometric and scattering insight

Mixed micellar systems play a pivotal role in numerous scientific and industrial applications due to their inimitable solution properties and potential for enhancing solubilization and emulsification processes. The present study unveils the mixed micellization behavior of two anionically charged surfactants, sodium dodecyl sulfate (SDS) and sodium oleate (SO), in aqueous solutions through a combination of solution viscosity, tensiometric and small-angle neutron scattering (SANS) techniques. The dynamic changes in the interfacial properties of the mixed micellar system as a function of the SDS-to-SO ratio are evaluated from surface tension measurements. The results offer an insight into the formation of the stable mixed micelles with the alteration in the critical micelle concentration (CMC) as a function of the composition of both surfactants and the nature of the interaction. Surface tension data disclose the thermodynamic aspects of micelle formation and the influence of surfactant interactions on the surface activity of the system. Complementing the surface tension measurements, SANS analysis was conducted to clarify the structural aspects of the SDS-SO mixed micelles. SANS inferred the micellar size, shape, and aggregation number (Nagg), thereby shedding light on the nanoscale organization of the micellar aggregates in the aqueous solution. By combining SANS and surface tension data, a comprehensive understanding of the mixed micellization behavior of SDS and SO is achieved, addressing both interfacial and structural aspects. A computational simulation approach has also been employed to obtain the optimized parameters, which provide a better understanding of the correlation of SDS and SO molecular orbital energy levels. The results underscore the importance of surface tension and structural characterization techniques to comprehend the behavior of mixed micelles fully.

Influence of tail group length, amide functionality and added salt ion identity on the behaviour of betaine surfactants

HypothesisThe behaviour of surfactants in solution and at interfaces is governed by a combination of steric and electrostatic effects experienced by surfactant molecules as they interact with solvent, other species in solution, and each other. It would therefore be anticipated that highly interacting groups would significantly influence surfactant behaviour. The widely used amide functionality has polar H-bond donor/acceptor properties, and therefore its inclusion into a surfactant structure should have a profound effect on surface activity and self-assembly of that surfactant when compared to the equivalent molecule without an amide linker. Further, chaotropic or kosmotropic salt ions that affect water structuring and hydrogen bonding may provide opportunities for further tuning surfactant interactions in such cases.ExperimentsA library of betaine surfactant with tail lengths n=14−22 both with and without an amidopropyl linker were synthesised to study the effect of the amide functionality on surfactant properties. Characterisation of the molecules interfacial properties were performed using pendant drop tensiometry and their solution state formulation properties were probed using small-angle neutron scattering (SANS) and rheological measurements.FindingsPresence of an amidopropyl linker had little effect on aggregation propensity (as evidenced by critical micelle concentration) and aggregate morphology of betaine surfactants, but did increase the Krafft temperature of these surfactants. SANS analysis indicated that aggregate morphology of alkyl betaine surfactants could be influenced by the addition of sodium salts with chaotropic counterions (I− and SCN−), but they were insensitive to more kosmotropic anions (SO42−, F− and Cl−), providing unique and novel solution control methods for this (supposedly salt-insensitive) class of surfactants.

Nucleation-Growth Versus Spinodal Decomposition in Fe-Cr Alloys: An Experimental Verification by Atom Probe Tomography and Small Angle Neutron Scattering.

Identifying the operative mode of phase separation [spinodal decomposition (SD) or nucleation-growth (NG)] remains an extremely important area of research. The present work examines this critically in the Fe-Cr system using atom probe tomography (APT) and small angle neutron scattering (SANS), and establishes the framework to distinguish the two different modes of α' phase separation in thermally aged Fe-35 at% Cr and Fe-20 at% Cr alloys. Independent APT analysis determines the mode of phase separation on the basis of (i) the presence/absence of periodic chemical fluctuation through radial distribution function analysis and (ii) interphase interface characteristics (diffuse/sharp). SANS analysis, in contrast, yields virtually indistinguishable correlation peaks for both the modes, which necessitates further investigation of the several different aspects of SANS profiles in the light of APT results. For the first time, key features of SANS profiles have been identified that can unambiguously distinguish SD from NG in the Fe-Cr system: (i) nature of temporal evolution of FWHM of the correlation peak and (ii) appropriate value of γ for fitting with the dynamic scaling model (γ = 6 for SD, Fe-35 at% Cr alloy; γ = 4 for NG, Fe-20 at% Cr alloy).

In Situ Small-Angle Neutron Scattering Analysis of Water Evaporation from Porous Exhaust-Gas-Catalyst Supports.

Porous media as catalyst supports are key to developing automotive exhaust purification systems. In particular, the water content of these porous media is attracting research attention because catalyst supports containing condensed water vapor at the early stage of cold start require a longer warm-up period. In this regard, water isotherms and evaporation in porous Al2O3 were investigated in this study using in situ small-angle neutron scattering (SANS) experiments. Unlike conventional evaluation methods, such as weighing and X-ray tomography, SANS distinguishes water in the primary and secondary pores using a contrast-matching method. Time-resolved measurements showed that water started to evaporate from the secondary pores in tens of seconds and subsequently from the primary pores in a hundred seconds. Exhaustive experiments conducted using nine alumina-based samples revealed that the drying rate depended on the secondary pore size of the porous Al2O3. The proposed approach can enable the evaluation of controlling factors to additionally optimize the performance of automotive exhaust gas catalysts, especially during cold start.

Design and physicochemical characterization of novel hybrid SLN-liposome nanocarriers for the smart co-delivery of two antitubercular drugs

In the present work a novel hybrid system for the delivery of two first-line antitubercular drugs, rifampicin (RIF) and isoniazid (INH), was designed. In order to control the release of the drugs and improve the efficiency of conventional carriers, like liposomes or solid lipid nanoparticles (SLNs), the new systems were developed by embedding SLNs into lecithin-based liposomes through the reverse-phase evaporation method. The hybrid system was characterized and compared to SLNs and liposomes in terms of size, encapsulation efficiency, morphology, and drug release. Detailed structural data and further evidence of the successful formation of the hybrid nanoparticles were obtained by applying small-angle neutron scattering (SANS). The hybrid system displayed a particle size comparable to liposomes and a high encapsulation efficiency. Morphological results obtained by atomic force microscopy (AFM) highlighted the possible presence of SLNs into the phospholipid bilayer; this hypothesis was supported by the slower in vitro release of the hydrophilic drug INH compared to liposomes and SLNs. Moreover, scattering differences of the inner core of the nanoparticles, evidenced in the SANS analysis, further corroborated the successful formation of the hybrid carrier. These novel systems were able to release their content as expected from an efficient dosage form in a perspective of an inhaled administration, improving the stability and the drug release profile with respect to plain liposomes. The physicochemical characterization of our systems opens new avenues towards a better understanding of the formulation of vesicles encapsulating SLNs.

Influence of Surfynol® 104 on aggregation behaviour of Triton X-100 micelles

Aqueous solution behaviour of non-ionic surfactant namely, p-tert-octylphenoxy polyethylene (9.5) ether, Triton X-100 (abbreviated as TX-100) was examined in the presence of an amphiphilic hydrophobic diol (Surfynol® 104) using viscosity, cloud point (CP), dynamic light scattering (DLS) and small-angle neutron scattering (SANS) measurements. Surfynol® 104 is a hydrophobic diol with limited aqueous solubility. It decreases the CP, elevates the solution viscosity of TX-100 solutions and leads to morphological changes of TX-100 micelles. The micellar transition was further confirmed from scattering techniques (DLS and SANS). With the aim to achieve different micellar transitions, the salt and the temperature effects were additional parameters used. It was revealed that the ellipsoidal to rod-like micellar transition observed at higher level of solubilization of Surfynol® 104 can be drag down to room temperature by incorporation of NaCl. Temperature and NaCl-aided micellar transitions were equally supported from SANS analysis. The observed structural transitions are explained in terms of the hydrophobic interaction between TX-100 and Surfynol® 104.

Quantitative evaluation of spinodal decomposition in thermally aged binary Fe-35 at.% Cr alloys by correlative atom probe tomography and small angle neutron scattering analyses

In this work, spinodal decomposition (SD) in Fe-35 at.% Cr alloy is quantified by correlatively combining two complimentary techniques namely, Atom Probe Tomography (APT) and Small Angle Neutron Scattering (SANS). In order to overcome the uncertainty often encountered in quantification of the characteristic SD parameters (wavelength λSD, amplitude A and volume fraction of Cr-rich α/-phase Φ), we adopt the following: (i) utilize the unique specific attribute of a technique suitable for evaluating any particular SD parameter; (ii) incorporate such reliably extracted parameter as input for evaluating other parameters wherever applicable. This novel correlative approach builds on each other's strength and provides improved accuracy. λSD is determined independently from APT and SANS analyses. For evaluation of A and Φ, APT analysis utilizes the value of λSD determined from SANS, whereas the phase compositions evaluated by APT are utilized in SANS analysis. With progressive phase separation, α/α/ compositional difference increases continually (from 19.8% after 10 h to 48.2% after 500 h) along with concomitant contraction of the interface (from 1.92 nm to 1.55 nm), underscoring the distinctive characteristics of SD process. Signature of rarely observed early stage of phase separation in the form of a dense population (9.78 × 1024/m3) of extremely small (0.67 nm radius) Cr-rich nanoclusters is registered after aging only for 1 h. In addition, temporal evolution of λSD clearly distinguishes early stage of SD (time exponent of 0.15) from the coarsening stage (time exponent of 0.29, 120 h onwards).

How do H2 oxidation molecular catalysts assemble onto carbon nanotube electrodes? A crosstalk between electrochemical and multi-physical characterization techniques.

Molecular catalysts show powerful catalytic efficiency and unsurpassed selectivity in many reactions of interest. As their implementation in electrocatalytic devices requires their immobilization onto a conductive support, controlling the grafting chemistry and its impact on their distribution at the surface of this support within the catalytic layer is key to enhancing and stabilizing the current they produce. This study focuses on molecular bioinspired nickel catalysts for hydrogen oxidation, bound to carbon nanotubes, a conductive support with high specific area. We couple advanced analysis by transmission electron microscopy (TEM), for direct imaging of the catalyst layer on individual nanotubes, and small angle neutron scattering (SANS), for indirect observation of structural features in a relevant aqueous medium. Low-dose TEM imaging shows a homogeneous, mobile coverage of catalysts, likely as a monolayer coating the nanotubes, while SANS unveils a regular nanostructure in the catalyst distribution on the surface with agglomerates that could be imaged by TEM upon aging. Together, electrochemistry, TEM and SANS analyses allowed drawing an unprecedented and intriguing picture with molecular catalysts evenly distributed at the nanoscale in two different populations required for optimal catalytic performance.

Quantitative Evaluation of Spinodal Decomposition in Thermally Aged Binary Fe-35 At.% Cr Alloys by Correlative APT and SANS Analyses

In this work, spinodal decomposition (SD) in Fe-35 at.% Cr alloy is quantified by correlatively combining two complimentary techniques namely, Atom Probe Tomography (APT) and Small Angle Neutron Scattering (SANS). In order to overcome the uncertainty often encountered in quantification of the characteristic SD parameters (wavelength λSD , amplitude A and volume fraction of Cr-rich α/ -phase Φ), we adopt the following: (i) utilize the unique specific attribute of a technique suitable for evaluating any particular SD parameter; (ii) incorporate such reliably extracted parameter as input for evaluating other parameters wherever applicable. This novel correlative approach builds on each other’s strength and provides improved accuracy. λSD is determined independently from APT and SANS analyses. For evaluation of A and Φ, APT analysis utilizes the value of λSD determined from SANS, whereas the phase compositions evaluated by APT are utilized in SANS analysis. With progressive phase separation, α/α/ compositional difference increases continually (from 19.8% after 10 h to 48.2% after 500 h) along with concomitant contraction of the interface (from 1.92 nm to 1.55 nm), underscoring the distinctive characteristics of SD process. Signature of rarely observed early stage of phase separation in the form of a dense population (9.78x1024 /m3 ) of extremely small (0.67 nm radius) Cr-rich nanoclusters is registered after aging only for 1 h. In addition, temporal evolution of λSD clearly distinguishes early stage of SD (time exponent of 0.15) from the coarsening stage (time exponent of 0.29, 120 h onwards).

Broadband dielectric spectroscopy and small-angle neutron scattering investigations of polyurethane–graphene foams

This work focuses on dielectric measurements and small-angle neutron scattering (SANS) analysis of polyurethane–graphene nanocomposite that is conducting and of low density. In this research graphene nanoplatelets were used. Polyurethane and graphene were mixed in appropriate weight proportions to make polyurethane–graphene (PU–graphene) nanocomposites. The porosity is decreased with an increase in graphene concentration. The dielectric characteristics such as dielectric constant, dielectric loss, loss tangent, and electric modulus were influenced by the graphene concentration. The conductivity (S/cm) increased rapidly by (~ 4 × 109 times) when the graphene concentration was increased to 30% and it indicates the formation of conducting pathways at high concentrations of graphene. SANS analysis showed that polyurethane has micellar structure and graphene assembles as fractals in the foams leading to conduction pathways in the nanocomposites. This research could benefit creation of lightweight materials for electronics.

Small-Angle Neutron Scattering Reveals the Structural Details of Thermosensitive Polymer-Grafted Cellulose Nanocrystal Suspensions.

Thanks to the use of small-angle neutron scattering (SANS), a detailed structural description of thermosensitive polymer-grafted cellulose nanocrystals (CNCs) was obtained and the behavior of aqueous suspensions of these derivatized biosourced particles upon temperature increase was revealed. Although literature data show that the surface grafting of thermosensitive polymers drastically enhances the colloidal properties of CNCs, direct space microscopic investigation techniques fail in providing sufficient structural information on these objects. In the case of CNCs decorated with temperature-sensitive polyetheramines following a peptide coupling reaction, a qualitative and quantitative analysis of SANS spectra shows that CNCs are homogeneously covered by a shell comprising polymer chains in a Gaussian conformation with a thickness equal to their radius of gyration in solution, thus revealing a mushroom regime. An increase of the temperature above the lower critical solution temperature (LCST) of the polyetheramine results in the formation of finite size bundles whose aggregation number depends on the particle concentration and suspension temperature deviation from the LCST. SANS analysis further reveals local changes at the CNC surface corresponding to a release of water molecules and a related denser polymer shell conformation. Noticeably, data show a full reversibility at all length scales when a sample was cooled down to below the LCST after being heated above it. Overall, the results obtained by SANS allow an in-depth structural investigation of derivatized CNCs, which is of high interest for the design of functional materials comprising these biosourced colloids.

Contrast-Variation Time-Resolved Small-Angle Neutron Scattering Analysis of Oil-Exchange Kinetics Between Oil-in-Water Emulsions Stabilized by Anionic Surfactants.

Contrast-variation time-resolved small-angle neutron scattering (CV-SANS) was used to examine oil-exchange kinetics between identical mixtures of hydrogenated/deuterated hexadecane emulsion systems. Oil-exchange rates were estimated by transforming recorded scattering profiles to a relaxation function and by fitting to exponential decay models. We find that the oil-exchange process was accelerated when the droplets were stabilized by anionic surfactants even at concentrations well below the surfactant critical micelle concentration. Moreover, the exchange rate was not significantly accelerated when surfactant micelles were present. This suggests that micellar-mediated transport mechanisms do not play the dominant role in these systems. Screening electrostatic repulsion by increasing the ionic strength of the medium also had a negligible effect on oil-exchange kinetics. In contrast, the use of oils with shorter alkane chain lengths (e.g., dodecane), having a higher solubility in water, significantly accelerated rates of oil transport between droplets. Oil-transport rates for hexadecane were also found to increase with temperature and to follow Arrhenius behavior. These results were rationalized as an increase in the droplet-collision frequency due to Brownian motion that results in direct oil transport without irreversible coalescence. Thus, primary mechanisms for oil exchange in insoluble anionic surfactant-stabilized emulsion systems are hypothesized to be through direct emulsion contact, reversible coalescence, and/or direct oil permeation through thin liquid films. CV-SANS is also demonstrated as a powerful technique for the study of transport kinetics in all kinds of emulsion systems.

Revisiting Temporal Evolution of Cu-Rich Precipitates in Fe-Cu Alloy: Correlative Small Angle Neutron Scattering and Atom-Probe Tomography Studies.

Binary Fe-Cu alloys are effective prototypes for investigating radiation-induced formation and growth of nanometric Cu-rich precipitates (CRPs) in nuclear reactor pressure vessels. In this report, the temporal evolution of CRPs during thermal aging of Fe-Cu binary alloys has been investigated by using complementary techniques such as atom probe tomography (APT) and small-angle neutron scattering (SANS). We report a detailed quantitative evolution of a rarely observed morphological transformation of Cu precipitates from spherical to ellipsoid with a significant change (approximately two times) in aspect ratio, an effect known to be associated with the 9R-3R structural transition of the precipitates. It is demonstrated through APT that the precipitates remain spherical up to 8 h, however, they subsequently convert to oblate ellipsoid upon further aging. SANS analysis also detected signs of this morphological transition in reciprocal space. Furthermore, SANS quantifies evolution of the precipitates and corroborates well with the APT results. Interestingly, the power-law exponent of the temporal evolution for mean size and number density agree reasonably well with the Lifshitz-Slyozov-Wagner model, in spite of the complex morphological evolution of the precipitates.

Correlative SANS and TEM investigation on precipitation kinetics of H-phase in Ni50.3Ti29.7Hf20 high temperature shape memory alloy

NiTiHf alloys are emerging as promising candidates for high-temperature shape memory actuator applications. The H-phase precipitation in these alloys significantly influences their mechanical strength and transformation temperatures. In this paper, we report a complementary study using time-resolved Small-Angle Neutron Scattering (SANS) along with transmission electron microscopy, to probe the H-phase evolution as a function of aging conditions in the Ni50.3Ti29.7Hf20 alloy. While, electron microscopy provided direct structural information about the precipitates, SANS analysis allowed in probing quantitatively the temporal evolution growth and coarsening of H-phase. It is demonstrated that while the diffusion of Ni atoms in the matrix predominantly governs the growth regime, the coarsening kinetics is primarily controlled by Hf diffusion. Further, relatively sluggish coarsening of the H-phase in this alloy, as compared to Ni4Ti3 precipitates in Ni-rich binary NiTi alloy, has been attributed to the slow migration of Hf in the matrix.

Drug-Induced Morphology Transition of Self-Assembled Glycopolymers: Insight into the Drug–Polymer Interaction

It is often assumed that a hydrophobic drug will be entrapped in the hydrophobic environment of a micelle. Little attention is usually drawn to the actual location of the drug and the effect of the drug on properties. In this publication, we show how the chosen drug curcumin is not only unexpectedly located in the shell of the micelle but also that the accumulation in the hydrophilic block can lead to changes in morphology during self-assembly. A block copolymer poly(1-O-methacryloyl-β-d-fructopyranose)-b-poly(methyl methacrylate), poly(1-O-MAFru)36-b-PMMA192, was loaded with different amounts of curcumin. The resulting self-assembled nanoparticles were analyzed using transmission electron microscopy, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS). Initial microscopy evidence revealed that the presence of the drug induces morphology changes from cylindrical micelles (no drug) to polymersomes, which decreased in size with increasing amount of drug. SAXS and SANS analysis, su...

Rational Design of Cholesterol Derivative for Improved Stability of Paclitaxel Cationic Liposomes.

This work explores synthesis of novel cholesterol derivative for the preparation of cationic liposomes and its interaction with Paclitaxel (PTX) within liposome membrane using molecular dynamic (MD) simulation and in-vitro studies. Cholesteryl Arginine Ethylester (CAE) was synthesized and characterized. Cationic liposomes were prepared using Soy PC (SPC) at a molar ratio of 77.5:15:7.5 of SPC/CAE/PTX. Conventional liposomes were composed of SPC/cholesterol/PTX (92:5:3M ratio). The interaction between paclitaxel, ligand and the membrane was studied using 10ns MD simulation. The interactions were studied using Differential Scanning Calorimetry (DSC) and Small Angle Neutron Scattering analysis. The efficacy of liposomes was evaluated by MTT assay and endothelial cell migration assay on different cell lines. The safety of the ligand was determined using the Comet Assay. The cationic liposomes improved loading efficiency and stability compared to conventional liposomes. The increased PTX loading could be attributed to the hydrogen bond between CAE and PTX and deeper penetration of PTX in the bilayer. The DSC study suggested that inclusion of CAE in the DPPC bilayer eliminates Tg. SANS data showed that CAE has more pronounced membrane thickening effect as compared to cholesterol. The cationic liposomes showed slightly improved cytotoxicity in three different cell lines and improved endothelial cell migration inhibition compared to conventional liposomes. Furthermore, the COMET assay showed that CAE alone does not show any genotoxicity. The novel cationic ligand (CAE) retains paclitaxel within the phospholipid bilayer and helps in improved drug loading and physical stability. Graphical Abstract ᅟ.

On the impact of surfactant type on the structure of aqueous ferrofluids

The impact of surfactant type on the structure organization of aqueous ferrofluids was considered based on the data of small-angle neutron scattering (SANS). The aggregates of different sizes and types were observed for magnetite magnetic nanoparticles of in heavy water stabilized by sodium oleate (SO) or dodecylbenzene sulphonic acid (DBSA). According to the surface tension measurements it was shown the significant difference of the critical micelle concentrations for SO and DBSA solutions. The observed structural difference of the aggregates in the ferrofluids was related to the behaviour of surfactant molecules in aqueous solutions including the structure and interaction parameters of micelles (micelle aggregation number, fractional charge, charge per micelle and surface potential, etc.) derived from the SANS analysis.

Magnetic scattering in the simultaneous measurement of small-angle neutron scattering and Bragg edge transmission from steel

Pulsed neutron sources enable the simultaneous measurement of small-angle neutron scattering (SANS) and Bragg edge transmission. This simultaneous measurement is useful for microstructural characterization in steel. Since most steels are ferromagnetic, magnetic scattering contributions should be considered in both SANS and Bragg edge transmission analyses. An expression for the magnetic scattering contribution to Bragg edge transmission analysis has been derived. The analysis using this expression was applied to Cu steel. The ferrite crystallite size estimated from this Bragg edge transmission analysis with the magnetic scattering contribution was larger than that estimated using conventional expressions. This result indicates that magnetic scattering has to be taken into account for quantitative Bragg edge transmission analysis. In the SANS analysis, the ratio of magnetic to nuclear scattering contributions revealed that the precipitates consist of body-centered cubic Cu0.7Fe0.3 and pure Cu, which probably has 9R structure including elastic strain and vacancies. These results show that effective use of the magnetic scattering contribution allows detailed analyses of steel microstructure.

Small-angle neutron scattering study of specific interaction and coordination structure formed by mono-acetyl-substituted dibenzo-20-crown-6-ether and cesium ions

This study uses small-angle neutron scattering (SANS) to elucidate the coordination structure of the complex of mono-acetyl-substituted dibenzo-20-crown-6-ether (ace-DB20C6) with cesium ions (Cs+). SANS profiles obtained for the complex of ace-DB20C6 and Cs+ (ace-DB20C6/Cs) in deuterated dimethyl sulfoxide indicated that Cs+ coordination resulted in a more compact structure than the free ace-DB20C6. The data were fitted well with SANS profiles calculated using Debye function for scattering on an absolute scattering intensity scale. For this theoretical calculation of the scattering profiles, the coordination structure proposed based on density functional theory calculation was used. Consequently, we conclude that the SANS analysis experimentally supports the proposed coordination structure of ace-DB20C6/Cs and suggests the following: (1) the complex of ace-DB20C6 and Cs+ is formed with an ace-DB20C6/Cs molar ratio of 1/1 and (2) the two benzene rings of ace-DB20C6 fold around Cs+ above the center of the crown ether ring of ace-DB20C6.