Curing kinetics and morphology of a nanovesicular epoxy/stearyl-block-poly(ethylene oxide) surfactant system.

Brittle epoxy based thermosets can be made tougher by introducing structural inhomogeneities at the micro- or nanoscale. In that respect, nano vesicles and worm-like micelles from self-assembling blockcopolymers have been shown to be very effective. This paper describes the curing kinetics and morphology of an epoxy composed of diglycidyl ether of bisphenol A (DGEBA) and 4,4'-methylenedianiline (MDA), modified by 20% of the surfactant stearyl-block-poly(ethylene oxide). Time resolved, synchrotron small-angle X-ray scattering demonstrates that at any time during the epoxy curing process, the surfactant predominantly adopts a bilayer vesicular nano-morphology. Transmission electron microscopy on fully cured systems reveals the coexistence of spherical and worm-like micelles. Differential scanning calorimetry experiments prove that the presence of surfactant reduces the epoxy curing rate but that ultimately full curing is accomplished. The material glass transition temperature falls below that of the pure resin due to plasticization. It is suggested that favorable secondary interactions between the PEO segments and the epoxy resin are responsible for the observed phenomena.

Encapsulation of the antioxidant ascorbyl palmitate in V-type granular cold-water swelling starch affects the properties of both.

This study reports on the functionality of V-type crystalline granular cold-water swelling starch (GCWSS) in complex with lipid (functionalized) molecules. Maize and potato GCWSS contain (empty) single helical amylose (AM) crystals which can serve as lipid complexing matrices. Different concentrations of ascorbyl palmitate (AscP) were inserted in the hydrophobic cavities of the GCWSS AM helices by a low temperature infusion method. Volumetric particle size distributions of the ensuing products in water were determined using laser light scattering. Upon contact with water, the parent maize GCWSS formed lumps more than did the parent potato GCWSS. It is hypothesized that variations in the spatial distribution of cold-water soluble V-type crystals are at the origin of this difference. In contrast, GCWSS-AscP inclusion complexes formed homogenous dispersions in water. Furthermore, the impact of inclusion complex formation on cold-water swelling properties was investigated. The close packing concentration increased and the swelling power and carbohydrate leaching decreased when the level of encapsulated AscP increased. Finally, in a Trolox equivalent antioxidant capacity test, encapsulated AscP still had up to 70% of the antioxidant capacity of free AscP.

Development of an infusion method for encapsulating ascorbyl palmitate in V-type granular cold-water swelling starch.

Certain lipophilic components can be inserted very efficiently as guest molecule in the existing single helical amylose cavities in VH-type crystalline granular cold-water swelling starch (GCWSS). In the present study, ascorbyl palmitate (AscP) was used as a model guest compound. The impacts of temperature (20 and 60°C) and ethanol [48 and 68% (v/v)] and AscP [1.0, 2.5, 5.0, 10.0% (w/w)] concentrations on encapsulation performance were investigated. First, native maize and potato starches were converted into VH-type GCWSS by aqueous ethanol [48% (v/v)] treatment at 95°C. Exposing GCWSS to AscP induced the formation of inclusion complexes when a particular solvent (and temperature) environment was met. In 48% (v/v) ethanol, raising the treatment temperature to 60°C did not significantly impact on the encapsulation performance. Maximum degrees of AscP encapsulation were 2.9 and 1.5% (w/w) for maize and potato starch, respectively, as determined by proton nuclear magnetic resonance measurements. As maize GCWSS contained more 'parent' VH-type crystals, it was capable of entrapping more AscP than potato GCWSS.

Structural and thermal transitions during the conversion from native to granular cold-water swelling maize starch.

Native maize starch was gradually converted into granular cold-water swelling starch (GCWSS) by aqueous ethanol treatments at elevated temperatures. At a treatment temperature of 95°C, decreasing ethanol concentrations from 68 to 48% (v/v) led to decreased post-treatment gelatinization enthalpies in excess water, reflecting remaining original A-type crystals. Concomitantly to native A-type crystal melting, VH-type crystals appeared. At an ethanol concentration of 48%, a granular cold-water swelling maize starch was successfully produced. All crystals in its intact granules were of the VH-type and appeared birefringent when studied in ethanol under polarized light. Removal of all residual solvent by high temperature drying did not influence swelling power, proving that a high temperature drying step is not necessary to induce cold-water swelling capacity. Based on in situ calorimetric measurements, the thermal requirements to produce GCWSS from different ethanol:water mixtures were elucidated. This work is the first to demonstrate that the amylose fraction contributes almost exclusively to VH-type crystal formation in GCWSS.

Characterization of nanoparticles in diluted clear solutions for Silicalite-1 zeolite synthesis using liquid 29Si NMR, SAXS and DLS.

Clear solutions for colloidal Silicalite-1 synthesis were prepared by reacting tetraethylorthosilicate in aqueous tetrapropylammonium hydroxide solution. A dilution series with water resulting in clear solutions with a TEOS ratio TPAOH ratio H2O molar ratio of 25 : 9 : 152 up to 25 : 9 : 15,000 was analysed using liquid 29Si nuclear magnetic resonance (NMR), synchrotron small angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Particle sizes were derived independently from DLS and from the combination of SAXS and NMR. NMR allowed quantitative characterization of silicon distributed over nanoparticles and dissolved oligomeric silicate polyanions. In all samples studied, the majority of silicon (78-90%) was incorporated in the nanoparticle fraction. In concentrated suspensions, silicate oligomers were mostly double-ring species (D3R, D4R, D5R, D6R). Dilution with water caused their depolymerisation. Contrarily, the internal condensation and size of nanoparticles increased with increasing dilution. SAXS revealed a decrease of effective nanoparticle surface charge upon dilution, reducing the effective particle interactions. With DLS, the reduction of nanoparticle interactions could be confirmed monitoring the collective diffusion mode. The observed evolution of nanoparticle characteristics provides insight in the acceleration of the Silicalite-1 crystallization upon dilution, in view of different crystallization models proposed in the literature.