Bernd U. Komanschek

Imaging the Assembly Process of the Organic-Mediated Synthesis of a Zeolite

The formation and consumption of precursors during zeolite crystallisation has been followed by small-angle X-ray scattering techniques. The nanometer-scale precursors are specific for the zeolite topology formed, and their aggregation is an essential step in the nucleation process shown here.

Density fluctuations: The nucleation event in isotactic polypropylene crystallization

The present study was undertaken tc investigate the mechanism for primary nucleation in polymer crystallization. Previous studies in this area have not been conclusive. Experiments on polypropylene with long induction times, studied by small- and wide-angle X-ray scattering (SAXS and WAXS), reveal the onset of long-range ordering prior to crystal growth. Rapid crystallizations studied by melt extrusion indicate the development of well-resolved oriented SAXS patterns associated with long-range order before the development of crystalline peaks in the WAXS region. The experimental results suggest pre-nucleation density fluctuations play an integral role in nucleation of polymer crystallizaticn.

Simultaneous studies of reaction kinetics and structure development in polymer processing.

The simultaneous time-resolved study of structure development and reaction kinetics during polymer processing is an experimental method that has great potential in developing a deeper understanding of the parameters that govern the formation of structure and therefore polymer properties. A combination of synchrotron radiation small-angle x-ray scattering and Fourier-transform infrared spectroscopy experiments have been performed on a series of model segmented block copolyurethanes. These studies confirm that the driving force for structure development in polyurethanes is the thermodynamics of phase separation rather than hydrogen bonding.

Nanometer scale precursors in the crystallization of Si-TPA-MFI

Abstract The crystallization of Si-TPA-MFI from a clear synthesis mixture has been studied in situ using X-ray scattering. Utilizing a combination of scattering techniques and high brilliance synchrotron X-ray radiation, we were able to study a unique range of length scales (four decades), which covers the scattering from all species present in the synthesis mixture. Combined small- and wide-angle X-ray scattering (SAXS-WAXS) results show that for cases with relatively high alkalinity the crystallization occurs while only 2.5 nm sized particles are present in the solution. In case of a lower alkalinity, additional 10 nm sized precursors are present, which act as a gel phase. These 10 nm sized particles probably play a role in the nucleation process, although their presence is not indispensable, as is shown by their absence in the high alkalinity synthesis. Applying in situ ultra-small-angle X-ray scattering (USAXS), the size of the crystals could be monitored, and when their linear growth has finished, aggregation of the discrete crystals to structures larger than 6 urn was found.

A synchrotron SAXS study of structure development in a copoly(isocyanurate-urea) formed by RIM

Abstract Structure development during reaction injection moulding of a copoly(isocyanurate-urea) was studied using time-resolved, synchrotron SAXS. During the rapid copolymerization of liquid reactants, incipient microphase separation was shown to occur at a critical conversion of isocyanate groups and to proceed via the kinetics associated with spinodal decomposition. Microphase separation was halted prematurely by vitrification of the polyisocyanurate phase, thus producing a copoly(isocyanurate-urea) with a non-equilibrium, co-continuous morphology with a size scale of ≈ 100 A.

SAXS/WAXS Investigations into the Self-Assembly of Zeolites

Zeolites are materials with monodisperse pores and well-defined active sites, and are therefore especially suitable for tailor-made applications such as selective catalysts or adsorbents for specific systems. Knowledge of the fundamental processes during the preparation of zeolites is still extremely scarce. This is mainly due to experimental difficulties, which we have solved by performing simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) during the in-situ preparation of zeolites in a dedicated, rotating heating cell at Station 8.2 of the SRS at Daresbury Laboratory. Using in-situ SAXS/WAXS, for the first time the nanometer-scale precursors during a zeolite synthesis have been identified, and their formation and consumption have been monitored during the complete course of the crystallization process, covering extended length scales. Based on a broad range of zeolite crystallizations, an assembly mechanism has been proposed which is probably general for organic-mediated zeolite synthesis.