Guilherme A. Calligaris

Theoretical and experimental developments for accurate determination of crystallinity of cellulose I materials

This work defines the crystallinity of cellulose I materials on a dry-weight basis. Theoretical and experimental developments in X-ray diffraction lead to a crystallinity determination method that is estimated to reach 1σ accuracies of better than 0.05 (crystallinity defined between 0 and 1). The method is based on Rietveld modelling, to resolve cellulose I Bragg peaks, and a standard truncated invariant integral. Corrections are derived to account for incoherent scattering, moisture content and other compositional deviations from pure cellulose. The experimental development uses X-ray diffraction in transmission fibre geometry with two-dimensional pattern Rietveld modelling, including a crystal-orientation distribution function. The crystallinities of a few commercial cellulose I materials were determined with the aim of illustrating the applicability of the method.

Delaying fat bloom formation in dark chocolate by adding sorbitan monostearate or cocoa butter stearin

Two formulations of dark chocolate were developed by adding cocoa butter stearin (CBSt) or sorbitan monostearate (SMS) and compared to a standard formulation in order to investigate fat bloom formation over time. Fat bloom was monitored by Whiteness Index (WI), melting behavior and polymorphism determinations, in bars stored during 90 days at 20 °C and under oscillating temperature between 20 and 32 °C. All samples stored at 20 °C did not develop fat bloom and the required β(V) form was maintained. Under oscillating storage condition, samples with CBSt (6.0%, w/w) and SMS (0.15%, w/w) delayed the surface fat bloom formation by at least 45 and 15 days, respectively, compared to standard chocolate, observed visually and through WI increments. The β(V) to β(VI) polymorphic transition correlated well with the WI, and also with changes in DSC thermograms, confirming the higher effectiveness of specific triacylglycerol (mainly StOSt) in delaying bloom formation.

X-ray dynamical diffraction in amino acid crystals: a step towards improving structural resolution of biological molecules via physical phase measurements

X-ray phase measurements have been applied to study hydrogen bonds and radiation damage in amino acid crystals.

Experimental evidence of transition between dynamical and kinematical diffraction regimes in ion-implanted Si observed through X-ray multiple-beam diffraction mappings

In this paper, the dependence of a Laue diffraction streak on the crystalline perfection of Xe-implanted Si(001) substrates is presented, based on the observation in the X-ray multiple diffraction (XRMD) mappings, as an experimental evidence of the transition between dynamical and kinematical diffraction regimes. A direct observation of the implanted region by transmission electron microscopy revealed an amorphous Si layer, which recrystallizes into a heavily twinned and faulted microstructure after thermal treatment at 800 °C. Besides the lattice damages, the annealing induces the formation of Xe bubbles. Both singularly affect the XRMD pattern, primarily the four-fold streaks profile of the (000)(002)(11¯1¯)(11¯3) four-beam simultaneous case when compared with the pristine Si pattern, highlighting the intra- and inter-block diffractions and the role played by the primary extinction effect. Such features provide information on the dominant diffraction regime. The findings are also discussed and compared ...

On the effect of Au2+ ion irradiation in an amorphous Fe–Si thin layer synthesized by ion implantation: a high resolution X-ray diffraction study

High resolution X-ray diffraction and synchrotron radiation multiple diffraction were used to investigate the structural effects induced by 5 MeV Au2+ ion irradiation into amorphous Fe–Si thin layers synthesized by Fe+ ion implantation in a Si(001) substrate. The concentration–depth profile and damage distribution induced by the Fe and Au ions were estimated by Monte-Carlo calculations (TRIM code) and were used to support the obtained experimental results. Grazing incidence X-ray diffraction and reflectivity measurements show the amorphous feature and interface quality of the as-implanted and Au-irradiated samples. Matrix and a distinct Si-distorted region contributions were detected by high resolution (004) rocking curves, as well as by Si(113) asymmetrical reciprocal space mapping patterns, for just the Au-irradiated samples. They have also shown defect distribution on the Si-distorted region interface plane. The exact multiple diffraction condition of the (1)(13) four-beam case was tailored and showed in a single ω:phi mapping, through the (1-13) coherent hybrid reflection, all previously detected effects of the Au-irradiation in the Si lattice. It is the first observation of this kind of hybrid reflection in an ion implanted and irradiated Si substrate. From the incidence (ω) and azimuthal (ϕ) angular positions measured, the Si-distorted region lattice parameters were determined along the in-plane and out-of-plane directions.

Rietveld Method Applied for Triacylglycerol Polymorphism Analysis

The characterization of the fat components becomes very useful in the formulation of shortening, margarines and fatty products due to their unique properties of plasticity, texture, solubility and aeration. The qualitative analysis obtained by X-ray diffraction (XRD) can be further improved in order to fulfill the lack of information on the triacylglycerol (TAG) in the hardfat systems aiming a complete polymorph characterization. In this work, as an attempt to quantify the distinct β and β’ TAG polymorphs, XRD was combined with Rietveld refinement method and applied to two types of samples: mixtures (M) and blended hardfats (B) samples involving fully hydrogenated of soybean (FHSO) and palm (FHPO) oils. M-samples were prepared with linear concentrations of FHSO (β) and FHPO (β’) and their Rietveld analysis have provided the expected content trend through the involved polymorphic phases with a very good agreement (~5%). This result validates the Rietveld method applicability on this kind of materials. The Rietveld method applied for Bsamples has shown that β’ polymorphic form prevails over the β-form, even for samples originally prepared with FHSO (β)/FHPO (β’) = 60/40 ratio (see figure). This result indicates the influence of the seeding process (earlier crystallization of β’ phase). This first quantitative approach for blended samples represents a very useful contribution towards the full characterization of fats.

X-ray n-beam diffraction to study nanodefects of Xe+ implantation in Si(001)

Investigations about the nanocavities/bubbles formation by inert gas ion implantation in Si matrix and its properties have constituted an ongoing challenge in material science. Dislocation/extended defects (likely the {113} defects) are produced by post-implant annealing, which affect directly the nanocavities/bubbles structural evolution. In this work, the formation of defects induced by Xenon gas ion implantation in a Si sample (#Si-pristine) was studied by high-resolution reciprocal space mappings (RSM) and nonconventional X-ray Multiple Diffraction (XRMD) using synchrotron radiation. For this, Xe+ ions (80 keV; 5x1015 cm-2) were implanted in Si(001) at room temperature. Subsequently, the as-implanted samples were thermally annealed in air atmosphere at 600, 700 and 800 oC for 30 min in order to nucleate Xe nanobubbles that were detected in annealed samples by TEM images. Differences in the diffracted intensity pattern, along the crystal truncation rod, were detected in the Si (113) asymmetrical RSM for as-implanted and annealed samples, in comparison to pristine Si, indicating defect contribution along in-plane an out-of-plane directions. The ω(incident):φ(azimuthal) coupled scans of two XRMD cases: 3-beam Bragg-Surface-Diffraction (BSD) (000)(002)(1-11) and the 4-beam (000)(002)(1-1-1)(1-13) have shown expected broader peaks (as-implanted sample) in comparison to the pristine sample, besides the ω-axis intensity asymmetry (c-axis strain induced). Furthermore, the analysis of all BSD mappings has provided: i) the annealing effect of reducing the lattice strain (600 and 700 oC samples), and ii) a huge surface effect through the diffuse scattering (800 oC-sample). As to the 4-beam case, a strong streak (diffraction condition trace) was observed for annealed sample patterns. This remarkable effect can be associated to the {113} defects, which are in the same direction of the secondary/coupling diffracting planes (XRMD phenomenon). It is believed that these defects break the spatial coherence, increasing the streak intensity. On the other hand, the streak is suppressed by the primary extinction effect in the pristine-Si and as-implanted samples. Financial support by Brazilian Synchrotron Light Laboratory (LNLS), CAPES, CNPq and FAPEMA.