ASAXS study of CaF2 nanoparticles embedded in a silicate glass matrix

The formation and growth of nanosized CaF2 crystallites by heat treatment of an oxyfluoride glass of composition 7.65Na2O–7.69K2O–10.58CaO–12.5CaF2– 5.77Al2O3–55.8SiO2 (wt%) was investigated using anomalous small-angle X-ray scattering (ASAXS). A recently developed vacuum version of the hybrid pixel detector Pilatus 1M was used for the ASAXS measurements below the Ca K-edge of 4038 eV down to 3800 eV. ASAXS investigation allows the determination of structural parameters such as size and size distribution of nanoparticles and characterizes the spatial distribution of the resonant element, Ca. The method reveals quantitatively that the growing CaF2 crystallites are surrounded by a shell of lower electron density. This depletion shell of growing thickness hinders and finally limits the growth of CaF2 crystallites. Moreover, in samples that were annealed for 10h and more, additional very small heterogeneities (1.6 nm diameter) were found

Anomale Röntgenkleinwinkelstreuungs(ASAXS)Untersuchungen von Nanokristallen in Glaskeramiken:Struktur und Zusammensetzung

Das Ziel der vorliegenden Arbeit ist eine quantitative Analyse von Nanokristallen in Bezug auf deren Struktur und Zusammensetzung. Diese Analyse wird von allen beteiligten Phasen (kristallin und amorph) von zwei verschiedenen Nano-Glaskeramiken mit Hilfe der anomalen Röntgenkleinwinkelstreuung (ASAXS) als wichtigste Methode durchgeführt. Die Eigenschaften der Glaskeramiken sind von der Größe, der Größenverteilung, der Volumenverteilung und der Zusammensetzung der gebildeten Nanokristalle sowie der restlichen Glasmatrix abhängig. Glaskeramiken, die magnetische Kristalle im Nanometerbereich enthalten, und damit spezielle magnetische Eigenschaften haben, versprechen viele zukünftige Anwendungen. Die ASAXS-Untersuchungen dieser Glaskeramiken mit magnetischen Nanopartikeln weisen die Bildung einer kristallinen Phase (MnxFe3-XO4) bei der Wärmebehandlung nach. Diese Nanopartikel sind durch eine dünne Schicht die mit SiO2 angereichert ist umgeben. Ferner wird das Verhältnis von Fe- zu Mn-Atomen in den nanometergroßen Kristallen durch ASAXS bestimmt. Die Untersuchungen zeigen, dass sich die Kristallstruktur ändert und die Zusammensetzung sich von Magnetit (Fe3O4) in Richtung der Jacobsite Phase (MnFe2O4) mit zunehmender Wärmebehandlungszeit ändert. SANS Untersuchungen mit polarisierten Neutronen weisen nach, dass sich eine Kern-Schale-Struktur gebildet hat, Weiterhin weist SANS nach, dass die Nanopartikel magnetisch sind sowie deren oberflächennahe Schicht magnetisch gestört ist, d.h. eine sogenannte dünne magnetische Totschicht wird ausgebildet. Umgeben ist solch ein Nanokristall von einer nichtmagnetischen Hüllenregion. Nanokristalle, wie BaF2 in Silikat-Gläsern in Anwesenheit von seltenen Erden, sind potenzielle Materialien für verschiedene photonische Anwendungen wie optische Verstärker oder Faserlaser. TEM-Studien mit Energie-Filterung implizieren, dass in einer Glaskeramik, die nanometergroße Kristalle aus BaF2 enthält, sich eine Region rund um die Kristalle bildet, die mit SiO2 angereichert ist. ASAXS Untersuchungen an diesen Proben bestätigen die Bildung einer solchen Schicht, die mit SiO2 angereichert ist. Darüber hinaus bieten diese Untersuchungen quantitative Informationen über die Zusammensetzung der Hüllen-Schicht und der Restglasmatrix sowie deren temperaturabhängigen Zusammensetzungsänderungen. In dieser Arbeit wird gezeigt wie ASAXS in Kombination mit anderen hier verwendeten Untersuchungsmethoden in der Lage ist, quantitative Informationen über Struktur und Zusammensetzung von Nanopartikeln in mehrphasigen Systemen zu liefern. Die beiden hier untersuchten Glaskeramiken gehören zu diesen mehrphasigen Systemen.The aim of the present work is a quantitative analysis of nanocrystallites with respect to their structures and compositions. This analysis will be done for all involved phases (crystalline and amorphous) of two different nanoglass ceramics by using anomalous small angle X-ray scattering (ASAXS) as a main method. Properties of glass ceramics depend on size, size distribution, volume fraction and on the composition of the formed nanocrystals and the remaining glass matrix. Glass ceramics that contain nano-scale magnetic crystals showing special magnetic properties have many future applications. ASAXS investigations on these glass ceramics containing magnetic nanoparticles show the formation of a MnxFe3-xO4 crystalline phase during heat treatment. The nanoparticles are surrounded by a thin layer enriched with SiO2. Furthermore, the ratio of Fe and Mn atoms in the nanosized crystals is determined by ASAXS. The investigations show that the crystal composition changes from magnetite (Fe3O4) towards the Jacobsite phase (MnFe2O4) with increasing annealing time. SANS investigations with polarized neutrons prove the existence of spherical core-shell like structures. SANS also demonstrates that the nanoparticles are magnetic and the surface near region is magnetically disturbed. A so called magnetic dead layer is formed. Such a nanocrystal is surrounded by a nonmagnetic shell region. Barium fluoride (BaF2) based nanocrystals doped with rare earth elements in silicate glasses are potential materials for various photonic applications such as optical amplifiers or fiber lasers. Energy filtering TEM studies imply that in glass ceramic containing nanosized crystals of BaF2 a shell like region surrounding the crystals exists that is enriched with SiO2. ASAXS investigations on these samples confirm the formation of such layers enriched with SiO2. Furthermore, these investigations provide quantitative information about the composition of the layer and the residual glass matrix and their temperature dependent composition changes. In the present work, it will be shown how ASAXS combined with other investigation methods is able to provide quantitative information on structure and compositions of nanoparticles in multiphase systems. The two investigated glass ceramics belong to this group of multiphase systems

Functionality of Immunoglobulin G and Immunoglobulin M Antibody Physisorbed on Cellulosic Films

The functionality and aging mechanism of antibodies physisorbed onto cellulosic films was investigated. Blood grouping antibodies immunoglobulin G (IgG) and immunoglobulin M (IgM) were adsorbed onto smooth cellulose acetate (CAF) and regenerated cellulose (RCF) films. Cellulose films and adsorbed IgG layers were characterized at the air and liquid interface by X-ray and neutron reflectivity (NR), respectively. Cellulose film 208 Å thick (in air) swell to 386 Å once equilibrated in water. IgG adsorbs from solution onto cellulose as a partial layer 62 Å thick. IgG and IgM antibodies were adsorbed onto cellulose and cellulose acetate films, air dried, and aged at room temperature for periods up to 20 days. Antibody functionality and surface hydrophobicity were measured everyday with the size of red blood cell (RBC) agglutinates (using RBC specific to IgG/IgM) and the water droplet contact angle, respectively. The functionality of the aged IgG/IgM decreases faster if physisorbed on cellulose than on cellulose acetate and correlates to surface hydrophobicity. IgG physisorbed on RCF or CAF age better and remain functional longer than physisorbed IgM. We found a correlation between antibody stability and hydrogen bond formation ability of the system, evaluated from antibody carbonyl concentration and cellulosic surface hydroxyl concentration. Antibody physisorbs on cellulose by weak dipole forces and hydrogen bonds. Strong hydrogen bonding contributes to the physisorption of antibody on cellulose into a non-functional configuration in which the molecule relaxes by rotation of hydophobic groups toward the air interface

Deuterated Bacterial Cellulose Dissolution in Ionic Liquids

Understanding the dissolution mechanism of deuterated bacterial cellulose (DBC) is important to engineer advanced material applications such as in quantifying and visualizing biomolecules at the cellulose interface for diagnostics. Small-angle neutron scattering (SANS) is applied to evaluate the distribution and volume fraction of dissolved DBC chains in 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) ionic liquid (IL-h) solvent in three different ways: (i) DBC in IL-h, (ii) DBC in a mixture of N,N-dimethylformamide (DMF) with IL-h (IL-h/DMF), and (iii) modified DBC by dissolution in IL-h with dichloromethane (DCM), (DCM-DBC). EMIM-Ac is a highly viscous solvent, and the incorporation of DMF reduces its viscosity. DCM incorporation into EMIM-Ac leads to partial acetylation of the cellulose chains. The DBC dissolves differently in all the modified solvents studied. The DBC and DCM-DBC dissolution in IL-h shows the presence of surface fractals (power law relation of intensity to a scattering vector, q, of q-3.4) indicating compact aggregated DBC structures. The DBC structure is more open in the DMF/IL-h solvent, which is reflected in the SANS curve mass fractal analysis with a power law of q-2.5. At intermediate values of the scattering vector, a q-1 power law is observed, indicative of rigid segments of dissolved DBC chains. Analysis of the intensity in this range provides insights as to the dissolution mechanism. The observed higher intensity measured in the solutions of DBC and DCM-DBC in IL-h can be attributed to the tight binding adsorption of the acetate ions on the DBC surface. Moreover, the unique aspect of this experiment, using deuterated cellulose in a mixture of deuterated DMF with protiated EMINM-Ac, provides direct proof for formation of a shell layer of IL-h surrounding the DBC surface. The results obtained shed light on the dissolution mechanism of cellulose in EMIM-Ac, highlighting its potential application in engineering biosensors and bio-diagnostics

Deep Eutectic Solvents for the Self-Assembly of Gold Nanoparticles: A SAXS, UV–Vis, and TEM Investigation

In this work, we report the formation and growth mechanisms of gold nanoparticles (AuNPs) in eco-friendly deep eutectic solvents (DES; choline chloride and urea). AuNPs are synthesized on the DES surface via a low-energy sputter deposition method. Detailed small angle X-ray scattering (SAXS), UV–Vis, and cryogenic transmission electron microscopy (cryo-TEM) investigations show the formation of AuNPs of 5 nm diameter. Data analysis reveals that for a prolonged gold-sputtering time there is no change in the size of the particles. Only the concentration of AuNPs increases linearly in time. More surprisingly, the self-assembly of AuNPs into a first and second shell ordered system is observed directly by in situ SAXS for prolonged gold-sputtering times. The self-assembly mechanism is explained by the templating nature of DES combined with the equilibrium between specific physical interaction forces between the AuNPs. A disulfide-based stabilizer, bis­((2-mercaptoethyl)­trimethylammonium) disulfide dichloride, was applied to suppress the self-assembly. Moreover, the stabilizer even reverses the self-assembled or agglomerated AuNPs back to stable 5 nm individual particles as directly evidenced by UV–Vis. The template behavior of DES is compared to that of nontemplating solvent castor oil. Our results will also pave the way to understand and control the self-assembly of metallic and bimetallic nanoparticles

Visualization and Quantification of IgG Antibody Adsorbed at the Cellulose–Liquid Interface

Quantification of adsorbed biomolecules (enzymes, proteins) at the cellulose interface is a major challenge in developing eco-friendly biodiagnostics. Here, a novel methodology is developed to visualize and quantify the adsorption of antibody from solution to the cellulose–liquid interface. The concept is to deuterate cellulose by replacing all nonexchangeable hydrogens from the glucose rings with deuterium in order to enhance the scattering contrast between the cellulose film surface and adsorbed antibody molecules. Deuterated cellulose (DC) was obtained from bacterial (Gluconacetobacter xylinus strain) cellulose, which was grown in heavy water (D₂O) media with a deuterated glycerol as a carbon source. For comparison, hydrogenated cellulose (HC) was obtained from cellulose acetate. Both HC and DC thin films were prepared on silicon substrate by spin coating. X-ray reflectivity (XR) shows the formation of homogeneous and smooth film. Neutron reflectivity (NR) at the liquid/film interface reveals swelling of the cellulose film by a factor of 2–3× its initial thickness. An Immunoglobulin G (IgG), used as a model antibody, was adsorbed at the liquid–solid interface of cellulose (HC) and deuterated cellulose (DC) films under equilibrium and surface saturation conditions. NR measurements of the IgG antibody layer adsorbed onto the DC film can clearly be visualized, in sharp contrast in comparison to the HC film. The average thickness of the IgG adsorbed layer onto cellulose films is 127 ± 5 Å and a partial monolayer is formed. Visualization and quantification of adsorbed IgG is shown by large difference in scattering length density (SLD) between DC (7.1 × 10^–6 Å^–2) and IgG (4.1 × 10^–6 Å^–2) in D₂O, which enhanced the scattering contrast in NR. Quartz crystal measurements (QCM-D) were used as a complementary method to NR to quantify the adsorbed IgG over the cellulose interface