Time-resolved Synchrotron SAXS Research Articles

Kinetic Pathways for Polyelectrolyte Coacervate Micelle Formation Revealed by Time-Resolved Synchrotron SAXS

The kinetic pathways for coacervation and micelle formation are still not fully understood. Driven by electrostatic interactions and entropically driven counterion release, complexation of opposite...

Conformational influence of fluorinated building blocks on the physical properties of polyesters

The interplay of the relative configuration of diastereomeric vicinal difluoride groups on the conformational properties of polyesters has been investigated and compared to their non-fluorinated and per-fluorinated counterparts. The incorporation of syn and meso vicinal difluoride units in the polymer backbone was expected to influence the rigidity and stacking behaviour of the polymers in a significant way, and therefore to result in different thermal properties, such as melting point and melting enthalpy. Both syn and meso-2,3-difluoro butanediol have been reacted with the diester dimethyl succinate, leading to the formation of polyesters that have been characterized with 1H, 13C and 19F NMR. The polyesters showed molar masses up to 20 kg/mol (SEC). Surprisingly, the syn and meso-polymers displayed identical crystallization and melting behaviour. In contrast, differences were observed in the crystallization kinetics and melting points of syn and meso oligomers. Relying on time-resolved synchrotron SAXS and WAXD experiments, the complex multiple melting behaviour of these oligomers was explained in terms of crystal size and surface effects. The slower crystallization kinetics for the meso oligomers was tentatively associated with a stronger tendency to adopt gauche configurations. Apparently, such effects no longer affect the crystallization kinetics when larger polymers crystallize. It was also found that the syn and meso-polymers have identical equilibrium melting points and melting enthalpies notwithstanding molecular and crystallographic differences.

Lamellar structure change of waxy corn starch during gelatinization by time-resolved synchrotron SAXS

In situ experiment of synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS) was used to study the lamellar structure change of starch during gelatinization. Waxy corn starch was used as a model material to exclude the effect of amylose. The thicknesses of crystalline (dc), amorphous (da) regions of the lamella and the long period distance (dac) were obtained based on a 1D linear correlation function. The SAXS and WAXS results reveal the multi-stage of gelatinization. Firstly, a preferable increase in the thickness of crystalline lamellae occurs because of the water penetration into the crystalline region. Then, the thickness of amorphous lamellae has a significant increase while that of crystalline lamellae decreases. Next, the thickness of amorphous lamellae starts to decrease probably due to the out-phasing of starch molecules from the lamellae. Finally, the thickness of amorphous lamellae decreases rapidly, with the formation of fractal gel on a larger scale (than that of the lamellae), which gradually decreases as the temperature further increases and is related to the concentration of starch molecular chains. This work system reveals the gelatinization mechanism of waxy corn starch and would be useful in starch amorphous materials processing.

In situ observations of particle size evolution during the hydrothermal crystallization of TiO2: A time-resolved synchrotron SAXS and WAXS study

We have monitored the homogeneous crystallization of TiO2 phases from aqueous TiCl4 solutions at 100°C using both time-resolved small-angle X-ray scattering (TR-SAXS) and time-resolved wide-angle X-ray scattering (TR-WAXS). The WAXS data revealed that metastable anatase was the first phase to crystallize, but it began transforming to rutile within the first hour of reaction. Scherrer analysis of WAXS peak widths indicated that anatase particles grew to an average size near 7nm on a time scale of minutes, after which their size remained static, while rutile grew rapidly from <3nm to ∼10nm within 1h, followed by slower growth at a rate of ∼0.15nm/h.Using a novel sample cell designed to withstand temperatures up to 150°C and hydrothermal vapor pressure, we collected in situ SAXS data for the same conditions as the WAXS experiments. Fourier analyses of the SAXS images revealed the rapid emergence of a broad, Gaussian-type particle size distribution ranging in diameter from 1 to ∼20nm with a mean near 7nm, in excellent agreement with our WAXS analysis. At 0.5h, a second population of <3nm particles emerged, and these crystals grew to ∼9nm after 7.5h, which we interpret as the nucleation and growth of rutile (as was also observed in the WAXS patterns). In contrast to studies that presume a solid-state transformation from anatase to rutile during growth, our results suggest that anatase and rutile co-precipitate during the early stages of crystallization, but once anatase crystals grow to a critical size of 7nm, they dissolve and the solution species re-precipitate onto primary rutile nanocrystals.

Multistep Crystallization Process Involving Sequential Formations of Density Fluctuations, “Intermediate Structures”, and Lamellar Crystallites: Poly(3-hydroxybutyrate) As Investigated by Time-Resolved Synchrotron SAXS and WAXD

We explored the isothermal crystallization process of poly(3-hydroxybutyrate) by means of simultaneous measurements of time-resolved wide-angle X-ray diffraction (tr-WAXD) and small-angle X-ray scattering (tr-SAXS) methods. The tr-WAXD analyses involve not only (1) a precise analysis of the integral widths but also the analyses such as (2) two-dimensional correlation spectroscopy (2D-COS) and (3) multivariate curve resolution–alternating least squares (MCR-ALS). The tr-SAXS analyses involve not only (4) the conventional one-dimensional correlation function analysis but also the analyses such as (5) 2D-COS between tr-SAXS and tr-WAXD profiles and (6) 2D-COS of tr-SAXS profiles themselves. These analyses elucidated a multistep crystallization process as classified by region I to III in order of the increasing time. In region I, the density fluctuations are first built up in the amorphous matrix, and then the density-rich regions locally develop “intermediate structures” having the mesomorphic orders between pure amorphous melts and pure crystals [lamellar crystallites (LC)], which then grow into layers of the intermediate structures [defined as mesomorphic layers (ML)] with the long spacings. These results were elucidated by analysis (5) and (6). In region II, LC start to be created from ML, which was elucidated by analysis (1) to (4), and both of the weight fractions of ML (Xinter) and LC (Xcrys) increase with time [analysis (3)]. In region III, Xinter and Xcrys decreases and increases with time, respectively [analysis (3)], because the transformation form ML to LC dominates the transformation from the density fluctuations to ML. The WAXD profiles due to ML in region I was identified by analysis (1), while those in regions II and III were identified by analysis (3).

In situ characterization of lipidic bupivacaine-loaded formulations

This work details the in situ dynamical behaviour of local anaesthetic bupivacaine (BUP)-loaded L2 and H2 phase precursors (preformulations of BUP) upon rapid exposure to phosphate buffer under physiological conditions (pH 7.4, 37 °C). The hydration-induced structural transitions are characterized by time-resolved synchrotron SAXS.

Synchrotron SAXS study of the microphase separation transition in diblock copolymers

The microphase separation transition (MST) in a nearly symmetric diblock copolymer is studied using time-resolved synchrotron SAXS. The transitions from the lamellar microphase to the isotropic melt and vice versa appear in the form of pronounced singularities in height and width of the main scattering maximum as a function of the temperature. The plot of the reciprocal scattering minimum S -1 (q * ) vs the reciprocal absolute temperature T -1 can be fitted to the corresponding theoretical function in the Hartree approximation although the present degree of polymerization N is much lower than the usually given limit of N>10 4