Guinier Radius Research Articles

Using atomistic solution scattering modelling to elucidate the role of the Fc glycans in human IgG4.

Human immunoglobulin G (IgG) exists as four subclasses IgG1-4, each of which has two Fab subunits joined by two hinges to a Fc subunit. IgG4 has the shortest hinge with 12 residues. The Fc subunit has two glycan chains, but the importance of glycosylation is not fully understood in IgG4. Here, to evaluate the stability and structure of non-glycosylated IgG4, we performed a multidisciplinary structural study of glycosylated and deglycosylated human IgG4 A33 for comparison with our similar study of human IgG1 A33. After deglycosylation, IgG4 was found to be monomeric by analytical ultracentrifugation; its sedimentation coefficient of 6.52 S was reduced by 0.27 S in reflection of its lower mass. X-ray and neutron solution scattering showed that the overall Guinier radius of gyration RG and its cross-sectional values after deglycosylation were almost unchanged. In the P(r) distance distribution curves, the two M1 and M2 peaks that monitor the two most common distances within IgG4 were unchanged following deglycosylation. Further insight from Monte Carlo simulations for glycosylated and deglycosylated IgG4 came from 111,382 and 117,135 possible structures respectively. Their comparison to the X-ray and neutron scattering curves identified several hundred best-fit models for both forms of IgG4. Principal component analyses showed that glycosylated and deglycosylated IgG4 exhibited different conformations from each other. Within the constraint of unchanged RG and M1-M2 values, the glycosylated IgG4 models showed more restricted Fc conformations compared to deglycosylated IgG4, but no other changes. Kratky plots supported this interpretation of greater disorder upon deglycosylation, also observed in IgG1. Overall, these more variable Fc conformations may demonstrate a generalisable impact of deglycosylation on Fc structures, but with no large conformational changes in IgG4 unlike those seen in IgG1.

Interphase and fibrous precipitation in a thermomechanically processed V–Nb–Mo microalloyed steel

A novel V–Nb–Mo steel was thermomechanically processed to promote ferrite grain refinement and precipitation during the austenite to ferrite transformation. Transmission electron microscopy and three-dimensional atom probe tomography confirmed the formation of two main types of precipitates: nano-scale interphase precipitates and fibrous precipitates (FP). Both the precipitates had a Baker–Nutting orientation relationship with the ferrite matrix, but with different variants. Interphase precipitates exhibited a disc shape with an average distance between precipitate rows of 15 ± 2 nm and an average Guinier radius of 3.9 ± 1.7 nm, whereas FP had a rod-shape 2.5 ± 0.5 nm in radius and 8–25 nm in length. It appeared that the FP are formed along the plane perpendicular to the interphase precipitates plane.

Magnetic Guinier law.

Small-angle scattering of X-rays and neutrons is a routine method for the determination of nanoparticle sizes. The so-called Guinier law represents the low-q approximation for the small-angle scattering curve from an assembly of particles. The Guinier law has originally been derived for nonmagnetic particle-matrix-type systems and it is successfully employed for the estimation of particle sizes in various scientific domains (e.g. soft-matter physics, biology, colloidal chemistry, materials science). An important prerequisite for it to apply is the presence of a discontinuous interface separating particles and matrix. Here, the Guinier law is introduced for the case of magnetic small-angle neutron scattering and its applicability is experimentally demonstrated for the example of nanocrystalline cobalt. It is well known that the magnetic microstructure of nanocrystalline ferromagnets is highly nonuniform on the nanometre length scale and characterized by a spectrum of continuously varying long-wavelength magnetization fluctuations, i.e. these systems do not manifest sharp interfaces in their magnetization profile. The magnetic Guinier radius depends on the applied magnetic field, on the magnetic interactions (exchange, magnetostatics) and on the magnetic anisotropy-field radius, which characterizes the size over which the magnetic anisotropy field is coherently aligned into the same direction. In contrast to the nonmagnetic conventional Guinier law, the magnetic version can be applied to fully dense random-anisotropy-type ferromagnets.

Self-Assembly of Cellulose in Super-Cooled Ionic Liquid under the Impact of Decelerated Antisolvent Infusion: An Approach toward Anisotropic Gels and Aerogels.

Assembly of (bio)polymers into long-range anisotropic nanostructured gels and aerogels is of great interest in advanced material engineering since it enables directional tuning of properties, such as diffusivity, light, heat, and sound propagation, cell proliferation, and mechanical properties. Here we present an approach toward anisotropic cellulose II gels and aerogels that employs specific diffusion and phase separation phenomena occurring during decelerated infusion of an antisolvent into isotropic supercooled solutions of cellulose in an ionic liquid to effectuate supramolecular assembly of cellulose in anisotropic colloidal network structures. At the example of the distillable ionic liquid 1,1,3,3-tetramethylguanidinium acetate, the antisolvent ethanol, and spherocylindrical porous molds, we demonstrate that the proposed facile, environmental-benign and versatile route affords gels and aerogels whose specific anisotropic nanomorphology and properties reflect the preferred supramolecular cellulose orientation during phase separation, which is perpendicular to the direction of antisolvent diffusion. Comprehensive X-ray scattering experiments revealed that the (aero)gels are composed of an interconnected, fibrous, highly crystalline (CrI ≈ 72%), cellulose II with a cross-sectional Guinier radius of the struts of about 2.5 nm, and an order parameter gradient from about 0.1 to 0.2. The obtained gels and aerogels feature high specific surface areas (350-630 m2 g-1) and excellent mechanical properties like high toughness (up to 471 kJ m-3 for a 60% compression, ρB = 80 mg cm-3) and resilience (up to 13.4 kJ m-3, ρB = 65 mg cm-3).

Nanoscale precipitation and its influence on strengthening mechanisms in an ultra-high strength low-carbon steel

Nanoscale precipitation and its influence on the strengthening mechanisms in low-carbon ultra-high-strength steel, hot-rolled at different temperatures and subjected to various isothermal aging conditions, are studied. The steel has a yield strength of ∼1730 MPa and elongation-to-failure of ∼13% under the peak aging condition, of which ∼740 MPa is contributed by precipitation strengthening. The precipitation strengthening mechanisms, including both the shearing mechanism and the Orowan mechanism, are quantitatively analyzed based on the mechanical properties and precipitate properties determined by small-angle neutron scattering, and atom probe tomography (APT). The APT results show that the average Guinier radius of the nanoscale precipitates under the peak aging condition is 1.4 nm at a number density of 6.19 × 1023m−3. These nanoscale precipitates consist of a Cu-enriched core, in which the depletion of Fe and enrichment of Cu change monotonically towards the center of the precipitates, whereas the concentrations of Ni, Al, and Mn exhibit diffused enrichment near the precipitate-matrix interfaces. Until the peak aging, precipitation strengthening mainly arises from shearing mechanism, among which the order and modulus strengthening mechanisms play the most significant role. Beyond peak aging, the shearing mechanism is not valid and the Orowan mechanism is the dominant contributor to the increase in yield strength due to the coarsening of the precipitates. The effect of the matrix microstructure on strength is also addressed and discussed.

Precipitation and clustering in a Ti-Mo steel investigated using atom probe tomography and small-angle neutron scattering

The isothermal evolution of nanometre-sized precipitates formed in a Ti-Mo microalloyed steel through interphase precipitation has been investigated using atom probe tomography and small-angle neutron scattering. The coiling time and applied strain have been varied to observe the precipitate evolution at a constant coiling temperature of 650 °C, where various evolution parameters such as particle radius, number density, volume fraction and chemical composition have been evaluated and compared. The possibility of early stage solute clustering and its effect on precipitate formation have also been investigated. Clustering of Ti, Mo and C atoms as Ti-C and Mo-C has been observed at the shortest coiling time of 5 min. These clusters are assumed to be precursors to the carbide precipitates observed in the system, which exhibit a metastable composition, containing a carbon fraction (C/Ti+Mo ratio) in the range of 0.2–1. In particles having a Guinier radius > 3 nm, however, the average chemical composition approached the stable MC carbide stoichiometry with Ti/Mo ratio ~2.5 and C/(Ti+Mo) ratio ~0.55. This study reveals that the precipitate coarsening kinetics are very slow, with average particle diameter < 5 nm even at longer coiling times (> 10 h) in both the undeformed and deformed conditions. This is believed to be due to the reduction in equilibrium Ti content in the matrix as a result of partial replacement of Ti by Mo (Ti/Mo ratio > 2) in the precipitate lattice, in the presence of excess C in the system.

Stability of nanoclusters in an oxide dispersion strengthened alloy under neutron irradiation

Here, we report atom probe tomography results of the nanoclusters in a neutron-irradiated oxide dispersion strengthened alloy. Following irradiation to 5dpa at target temperatures of 300°C and 450°C, fewer large nanoclusters were found and the residual nanoclusters tend to reach an equilibrium Guinier radius of 1.8nm. With increasing dose, evident decrease in peak oxygen and titanium (but not yttrium) concentrations in the nanoclusters was observed, which was explained by atomic weight, solubility, diffusivity, and chemical bonding arguments. The chemical modifications indicate the equilibrium size is indeed a balance of two competing processes: radiation enhanced diffusion and collisional dissolution.

Estimation of the density distribution from small-angle scattering data

The one-dimensional density distribution for symmetrical scatterers is estimated from small-angle scattering data. The symmetry of the scatterers may be one dimensional (lamellar), two dimensional (cylindrical) or three dimensional (spherical). Previously this problem has been treated either by a two-step approach with the distance distribution as an intermediate [Glatter (1981).J. Appl. Cryst.14, 101–108] or in a single step using spherical harmonics [Svergun, Feigin &amp; Schedrin (1982).Acta Cryst.A38, 827–835]. A combination of these two methods is presented here, where the density distribution is estimated using constraints without the explicit use of an intermediate distribution. A maximum entropy constraint is introduced for this problem and the results are compared with the results of the conventional smoothness constraint. Bayesian methods are used for estimation of the overall noise level of the experimental data and for the maximum dimension of the density distribution. The method described is tested on both simulated and experimental data and shown to provide reliable estimates for the Guinier radius and maximum dimension. In both cases the effects of minor deviations from the assumed symmetry as well as incorrect background subtraction are studied.

Intrinsically Microporous Polymer Retains Porosity in Vacuum Thermolysis to Electroactive Heterocarbon.

Vacuum carbonization of organic precursors usually causes considerable structural damage and collapse of morphological features. However, for a polymer with intrinsic microporosity (PIM-EA-TB with a Brunauer-Emmet-Teller (BET) surface area of 1027 m(2)g(-1)), it is shown here that the rigidity of the molecular backbone is retained even during 500 °C vacuum carbonization, yielding a novel type of microporous heterocarbon (either as powder or as thin film membrane) with properties between those of a conducting polymer and those of a carbon. After carbonization, the scanning electron microscopy (SEM) morphology and the small-angle X-ray scattering (SAXS) Guinier radius remain largely unchanged as does the cumulative pore volume. However, the BET surface area is decreased to 242 m(2)g(-1), but microporosity is considerably increased. The new material is shown to exhibit noticeable electrochemical features including two pH-dependent capacitance domains switching from ca. 33 Fg(-1) (when oxidized) to ca. 147 Fg(-1) (when reduced), a low electron transfer reactivity toward oxygen and hydrogen peroxide, and a four-point-probe resistivity (dry) of approximately 40 MΩ/square for a 1-2 μm thick film.

Stability of nanoclusters in 14YWT oxide dispersion strengthened steel under heavy ion-irradiation by atom probe tomography

14YWT oxide dispersion strengthened (ODS) ferritic steel was irradiated with of 5MeV Ni2+ ions, at 300°C, 450°C, and 600°C to a damage level of 100dpa. The stability of Ti–Y–O nanoclusters was investigated by applying atom probe tomography (APT) in voltage mode, of the samples before and after irradiations. The average size and number density of the nanoclusters was determined using the maximum separation method. These techniques allowed for the imaging of nanoclusters to sizes well below the resolution limit of conventional transmission electron microscopy techniques. The most significant changes were observed for samples irradiated at 300°C where the size (average Guinier radius) and number density of nanoclusters were observed to decrease from 1.1nm to 0.8nm and 12×1023 to 3.6×1023, respectively. In this study, the nanoclusters are more stable at higher temperature.

Investigation of Precipitate in Polygonal Ferrite in a Ti-Microalloyed Steel Using TEM and APT

Transmission electron micrograph and atom probe tomography were used to characterize the distribution, sizes, and compositions of precipitates in a Ti microalloyed steel. At 650 and 700°C with holding time 600 and 1800 s, respectively, the dispersion precipitates were obtained in all specimens, and the interphase precipitates were only observed at short holding time, but this interphase precipitation was unstable at long holding time. The kinetics of precipitates in ferrite depended on both coiling temperature and holding time. A lot of small precipitates were obtained at 650 °C with holding time 600 s, and these nano-precipitates can strengthen the ferrite matrix largely. The average Guinier radius of nano-precipitate was about 4.3 nm, and the large precipitates (Guinier radius ∼7–9 nm) with small precipitates (Guinier radius ∼3–5 nm) within an interphase sheet were also observed due to the growth of some precipitates at the cost of small precipitates. The nano-precipitates were mainly titanium carbide, and the atomic ratio of Ti/C was about 0.55, and this value was changed regularly in one precipitate.

Analysis of strengthening in AA6111 during the early stages of aging: Atom probe tomography and yield stress modelling

In this work, a series of aging treatments has been conducted on AA6111 alloy samples for various times at ambient temperature (so-called natural aging) and at temperatures between 60 and 180°C (artificially aged). The time at artificial ageing was chosen such that samples with approximately the same yield stress were produced. The microstructures of these alloy samples have been carefully characterized using atom probe tomography together with advanced cluster-finding techniques in order to obtain quantitative information about the changes in distribution of both the solute clusters and early-stage precipitates that are formed. The size distribution of clusters has been mapped onto the glide plane and then the stress necessary for a dislocation to pass through the range of obstacles has been estimated using an areal glide model where the dislocation–obstacle interaction strength has been assumed to be related to the obstacle size on the glide plane. It is demonstrated that the contribution of cluster strengthening during artificial aging at higher temperatures is dominated by the high number density of small clusters (Guinier radius <1nm), whereas the situation during room temperature natural aging is more complex.

Three-dimensional atom probe microscopy study of interphase precipitation and nanoclusters in thermomechanically treated titanium–molybdenum steels

Atom probe microscopy was used to generate tomographic analyses of solute clustering and precipitation reactions in a Ti–Mo added microalloyed steel under simulated strip-rolling conditions. It was observed that the interphase row spacing of precipitates was reduced with the application of a pre-strain. The atom probe data also revealed the coexistence of nanoclusters and precipitate particles, even after isothermal holding for 3600s. These microstructural features occurred both within 3-D interphase precipitate sheets, and in randomly selected fields of view. A bimodal distribution of larger (∼8–10nm) precipitates coexisted with smaller nanoclusters (∼3nm) within the interphase sheets/rows. Both the nanoclusters and the precipitates possessed a disc morphology, although nanoclusters with less than ∼30 atoms were more irregular in shape. The size of the nanoclusters and the precipitates was expressed as a Guinier radius, and this varied between 0.5 and 8nm for both strain conditions, with the average size ∼1.8nm. The composition of the nanoclusters varied over a wide range, yet was mostly rich in C. All of the nanoclusters and precipitates consisted of a mixture of Ti, Mo and C and the average precipitate composition was close to that of MC carbide stoichiometry, where M represents a mixture of Ti and Mo. In the majority of cases, the Ti/Mo ratio in the MC carbides was>1. As the Guinier radius increased above 2.5nm, the composition range became narrower, towards the MC carbide stoichiometry, with a small amount of Fe (∼3–12at.%).

Structural and morphological characterization of chloride salt of conducting poly(o-methoxyaniline) obtained at different time synthesis

Emeraldine-salt poly(o-methoxyaniline) form (ES-POMA) was chemically synthesized at time synthesis ranging from 0.5 to 72h and characterized by X-ray Diffraction (XRD), LeBail fit, Small-angle X-ray Diffraction (SAXD), Small-angle X-ray Scattering (SAXS) and Scanning Electron Microscopy (SEM). Crystallinity and crystal data (for 3h of synthesis, a=7.0073Å, b=10.6078Å, c=22.5234Å, α=83.3783°, β=84.7231° and γ=89.0455°) were obtained by XRD and showed that the percentage of crystallinity increased from 48% to 63%. LeBail fit showed that the crystallites have lost their globular shape to give rise to twinned crystallites shape ranging from 26 to 56Å. By SAXS it was obtained the particle Guinier Radius of Giration (Rg) of (310±1)Å. The maximum particle size (Dmax) of synthesized polymers was obtained from the pair-distance distribution function (p(r)) and ranged from 1000 to 830Å. SEM images showed a globular vesicular morphology with micrometric sizes. It was observed that increasing time synthesis promotes the size reduction of these structures with the electrical conductivity of the samples increasing from 5.18×10−7 to 8.89×10−7S/cm.

Small-angle X-ray scattering investigation of aging behavior of Al-Cu-Mg-Ag alloys using synchrotron radiation

The aging behavior of Al-Cu-Mg-Ag alloys with high Cu/Mg was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) using synchrotron radiation. TEM study reveals that the major strengthening phases of the alloy after aging at 160 °C for 10 h are Ω and less θ′. SAXS study shows that the scattering patterns are composed of several concentric circles at the beginning of aging process, which is replaced by the butterfly-wings scattering patterns with the increase of aging time. The butterfly-wings scattering patterns are composed of several branches. The angles between the branches are roughly equal to that between the habit planes of precipitates. The evolution of Guinier radius with aging time indicates the good coarsening resistance of the precipitates. The evolution of integrated intensity is consistent with the classical two-step precipitation process.

Formfactors of Hollow and Massive Rectangular Parallelepipeds at Variable Degree of Anisometry

AbstractThe present work is a comparative study on the scattering behaviour of hollow and filled rectangular parallelepipeds. Comparison is based on the model formfactors of rectangular parallelepipeds, which cover the entire regime of variable wall thickness. The entire regime of wall thicknesses has been made available by the present work, which completed the set of formulas by calculating the formfactor for the limit of hollow parallelepipeds with infinitely thin walls, which was still lacking. The formfactors are expressed as a function of the momentum transferq. Discrimination between massive and hollow structures by means of theq-dependent scattering dataSF(q)gets possible once the Guinier radius and the particle volume can be established at the lower limit ofqor a power law ofSF(q)∼qαcan be extracted towards largeq. Whereas the former requires extrapolation of the scattering data toq= 0 with high accuracy, the latter needs experiments over a very broadq-regime. If experimental data is restricted to aq-regime which includes only the first peak in a Kratky representation ofq2SF(q)vs.qwithout giving way to an accurate extrapolation toq= 0 nor to a clear power law inq, discrimination between a hollow and a massive structure gets extremely difficult. Yet, the effect of anisometry is striking and enables extraction of a crude guess of the degree of anisometry already from the first Kratky peak. This could be achieved by introducing a dimensionless parameter established from the width and location of the first Kratky peak.

Cavitation during deformation of polymers on the example of polypropylene

AbstractCavitation during uniaxial deformation of isotactic polypropylene (PP) was studied in samples having different amounts of α and β crystals. It has been shown that deformation is always accompanied by neck formation. Because the very beginning the plastic deformation is accompanied by cavitation. The scale of cavitation, determined with the use of X‐ray scattering and volume measurements increases with an increase of the content of β phase in the examined samples. Cavities change their shape with deformation—at first they are elongated perpendicularly to the direction of stretching, next, at the strain of 1.5, they reorient in the direction of deformation, which is connected with changes in the surrounding lamellar structure. The calculations of Guinier's radius showed that two populations of voids are present in deformed PP samples, characterized by the gyration radii of 5 and 13 nm for small deformations. Estimations based on the volume increase and sizes of cavities indicate that typically more than one cavity are present in amorphous layers adhering to lamella surfaces. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

On the validity of simple precipitate size measurements by small-angle scattering in metallic systems

This paper assesses how simple small-angle scattering particle size evaluation models, such as Porod or Guinier radii, which have a normally limited validity range, may see this range extended to largerqvalues. This is shown to be particularly true for metallic systems, where the dispersion in particle size is always large. Because of the size dispersion, the relationship between the average particle size and the Guinier radius is shown to change. For systems with relatively large size dispersion, the paper shows that the Porod and Guinier radii, and simple extensions thereof, give valuable information on particle size and particle size distribution. This is demonstrated to be valid for particles with moderate aspect ratios. These simple evaluations are quick and very well adapted to large data sets, such as those originating from time-resolved or scanning small-angle experiments.

Small-angle X-ray scattering study of the early stages of precipitation in a Mg–Nd–Gd (EV31) alloy

A quantitative description of the Mg-rare earth EV31 alloy during the first stages of the precipitation sequence using in situ small-angle X-ray scattering (SAXS) is presented. In situ evolutions of the size, volume fraction and number density of precipitates formed at 150 °C and 200 °C were obtained. A kinetic mechanism suggests that the precursor nanoparticles are nucleated at the beginning of the artificial ageing and, at 200 °C, these particles grow mainly by accretion of the solute from the matrix without further nucleation. The particles grow within two regimes: (i) at the beginning of ageing, the growth is associated with solute diffusion with an apparent activation energies of 0.78 eV (diffusion assisted by vacancies); (ii) further growth is associated with solute diffusion with an apparent activation energies of 1.16 eV (bare solute diffusion). After about 2 h at 200 °C, corresponding to the condition of maximum hardness for this alloy, the present results indicate a volume fraction of about 1.5% occupied by particles with an average Guinier radius of 2 nm. The evolution of the volume fraction at 150 °C, studied for a similar time interval, is weaker than the one found at 200 °C.

Delineating the First Few Seconds of Supramolecular Self-Assembly of Mesostructured Titanium Oxide Thin Films through Time-Resolved Small Angle X-ray Scattering

The early stages of evaporation induced self-assembly of titanium oxide mesophases from a precursor solution containing TiCl4 and the Pluronic triblock copolymer F-127 in HCl-water-ethanol solution have been studied using time-resolved SAXS techniques. Two experimental protocols were used to conduct these experiments. In one of these, the precursor solution was pumped around a closed loop as solvent was allowed to evaporate at a constant humidity-controlled rate. In the second protocol, a film of precursor solution was measured periodically as it dried completely to a residue under a stream of dry air. This permitted the detailed monitoring of changes in solution chemistry as a function of the elimination of volatile components followed by the actual drying process itself. The SAXS data were modeled in terms of two Guinier radii for soft nanoparticles while a broad Gaussian feature in the scatter profiles was accounted for by particle-article scattering interference due to close packing. For the initial precursor solution, one Guinier radius was found to be about 17 angstroms while the other ranged from 4 to 11 angstroms. Changing the rate of evaporation affected the two radii differently with a more pronounced effect on the smaller particle size range. Analysis gave an interparticle distance in the range 55-80 angstroms for the initial precursor solution which decreased steadily at both of the humidities investigated as evaporation proceeded and the particle packing increased. These results represent the first attempts to monitor in a precise fashion the growth of nano building blocks during the initial stages of the self-assembly process of a titanium oxide mesophase.