Molecular and Morphological Aspects of Annealing-Induced Stabilization of Starch Crystallites

in Biomacromolecules (2012), 13

A unique series of potato (mutant) starches with highly different amylopectin/amylose (AP/AM) ratios was annealed in excess water at stepwise increasing temperatures to increase the starch melting (or ... [more ▼]

A unique series of potato (mutant) starches with highly different amylopectin/amylose (AP/AM) ratios was annealed in excess water at stepwise increasing temperatures to increase the starch melting (or gelatinization) temperatures in aqueous suspensions. Small-angle X-ray scattering (SAXS) experiments revealed that the lamellar starch crystals gain stability upon annealing via thickening for high-AM starch, whereas the crystal surface energy decreases for AM-free starch. In starches with intermediate AP/AM ratio, both mechanisms occur, but the surface energy reduction mechanism prevails. Crystal thickening seems to be associated with the cocrystallization of AM with AP, leading to very disordered nanomorphologies for which a new SAXS data interpretation scheme needed to be developed. Annealing affects neither the crystal internal structure nor the spherulitic morphology on a micrometer length scale. [less ▲]

Modeling the morphology and mechanical behavior of shape memory polyurethanes based on solid-state NMR and synchrotron SAXS/WAXD

in Journal of Materials Chemistry (2010), 20

A combination of solid-state proton Wide-line Nuclear Magnetic Resonance (NMR) relaxometry and synchrotron Small-angle (SAXS) and Wide-angle (WAXD) X-ray scattering was used to elucidate the microphase ... [more ▼]

A combination of solid-state proton Wide-line Nuclear Magnetic Resonance (NMR) relaxometry and synchrotron Small-angle (SAXS) and Wide-angle (WAXD) X-ray scattering was used to elucidate the microphase morphology of shape memory thermoplastic multi-block polyurethanes based on poly(3-caprolactone), as switching segment and polyurethane based permanent or hard segments (HS). The polyurethanes are produced from the condensation of 1,4-butanediol (BDO) with hexamethylenediisocyanate (HDI). The morphology – induced by the hard-segment crystallization – converts from dispersed randomly placed hard-segment domains into progressively more periodic, but interconnected HS nanophases with increasing HS content. Irrespective of the actual morphology, the SAXS data could be described satisfactorily by using a clipped Gaussian random field (GRF) model. The NMR data demonstrate that the HS domain fraction corresponds to the chemical feed, pointing at a complete phase separation. The material mechanical behavior during repeated deformation cycles can be explained on morphological grounds and involves a spatially heterogeneous plastic deformation of the hard domains. [less ▲]

Sulfonated silica/carbon nanocomposites as novel catalysts for hydrolysis of cellulose to glucose

in Green Chemistry (2010), 12

Sulfonated silica/carbon nanocomposites were successfully developed as reusable, solid acid catalysts for the hydrolytic degradation of cellulose into high yields of glucose.

SAXS Data Analysis of Ordered and Disordered Morphologies With Gaussian Random Field Models

Conference (2009, September)

Critical opalescence points to thermodynamic instability:relevance to small-angle X-ray scattering of resorcinol–formaldehyde gel formation at low pH

in Journal of Applied Crystallography (2008), 41(4), 663-668

During the formation at low pH of resorcinol–formaldehyde gels with a structure in the micrometre range, small-angle X-ray scattering exhibits a nonmonotonic intensity variation as a function of reaction ... [more ▼]

During the formation at low pH of resorcinol–formaldehyde gels with a structure in the micrometre range, small-angle X-ray scattering exhibits a nonmonotonic intensity variation as a function of reaction time. The data are analyzed in terms of scattering by statistical fluctuations of polymer concentration, the amplitude of which is maximal close to the critical point for phase separation between polymer and solvent. The data do not carry any morphological information, but they unambiguously show that the driving force of the gel formation is a thermodynamic instability of the polymerizing solution. [less ▲]

Relevance of Spinodal Decomposition for Support Formation and Metal Dispersion in Cogelled Pd/SiO2 Catalysts

in Journal of Physical Chemistry C (2007), 111

The structure formation of cogelled Pd/SiO2 catalysts is followed in situ at the nanometer scale using timeresolved small-angle X-ray scattering (SAXS). The SAXS patterns are analyzed in terms of a ... [more ▼]

The structure formation of cogelled Pd/SiO2 catalysts is followed in situ at the nanometer scale using timeresolved small-angle X-ray scattering (SAXS). The SAXS patterns are analyzed in terms of a reaction-induced spinodal decomposition that is responsible for the formation of the silica support and most likely for the metal dispersion as well. The results are discussed in the light of recent electron tomography characterizations of the catalysts. The latter technique reveals regularity in the metal dispersion, the origin of which is likely to be the very occurrence of a spinodal phase separation. [less ▲]

Phase separation during silica gel formation followed by time-resolved SAXS

in Nuclear Instruments & Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2005), 238(1-4), 141-145

Time-resolved small angle X-ray scattering data are collected during the formation of silica gels from the base catalyzed polymerization of tetraethoxysilane in ethanol with 3-(2-aminoethylamino ... [more ▼]

Time-resolved small angle X-ray scattering data are collected during the formation of silica gels from the base catalyzed polymerization of tetraethoxysilane in ethanol with 3-(2-aminoethylamino)propyltrimethoxysilane and 3-aminopropyltriethoxysilane as additives. It is shown that a polymerization-induced spinodal demixing occurs during the gel formation. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

Time-resolved SAXS measurements of phase separations during silica gel formation

Poster (2003, October)