Condensation-Induced Decrease of Small-Angle X-ray Scattering Intensity in Gelling Silica Solutions

Gommes, Cédric; Pirard, Jean‐Paul; Goderis, Bart

doi:10.1021/jp104541z

Cited by 5 publications

(5 citation statements)

References 24 publications

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“…The estimates are based on the macroscopic loading of 0.18 g Cu / g SiO2 . The electron densities of the various materials are calculated in the usual way from the mass density ρ̃, the molar mass M , and the number of electrons Ne – in one mole of material . The electron density of the silica that forms the support is ρ SiO2 = 1.1 F·cm –3 (Faraday per cubic centimeter).…”

Section: The Case Of Copper-loaded Sba-15mentioning

confidence: 99%

“…The electron densities of the various materials are calculated in the usual way from the mass density ρ, the molar mass M, and the number of electrons Ne − in one mole of material. 59 The electron density of the silica that forms the support is ρ SiO2 = 1.1 F•cm −3 (Faraday per cubic centimeter). In the case of Cu/S, several crystallographic forms are possible for the nitrate, with different electron densities.…”

Section: ■ the Case Of Empty Sba-15 Silicamentioning

confidence: 99%

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Small-Angle Scattering Analysis of Empty or Loaded Hierarchical Porous Materials

2016

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Small-angle scattering of X-rays (SAXS) or neutrons (SANS) is one of the few experimental methods that can in principle be used for the in situ study at the mesoscopic scale of physicochemical phenomena occurring inside nanoporous solids. However, the potential of the method is often limited by the lack of suitable data analysis methods to convert scattering data into real-space structural information. This is notably the case for most porous materials of practical interest, which exhibit a hierarchical structure with micro, meso, and macropores, with often a secondary material confined in the pores, such as in supported catalysts, as well as fuel-cell and battery materials. In the present paper, we propose a general analysis of X-ray scattering by this type of material. Assuming that each structural level is statistically independent from the others and has a distinct characteristic length scale, compact mathematical expressions are derived for the scattering of the entire hierarchical structure. The results are particularized to the SAXS analysis of SBA-15-ordered mesoporous silica loaded with copper nitrate as well as of supported catalysts obtained after heat treatment of that material. The SAXS data analysis shows that the nitrate fills both the micro- and mesopores of the material, while the metallic copper obtained after heat treatment is found only in the mesopores. Moreover, the mesoscopic-scale spatial distribution of the metal depends on the heat treatment, in line with earlier electron tomography studies. The main ideas underlying the SAXS data analysis were presented in a recent communication (Gommes Angew. Chem., Int. Ed. 2015, 54, 11804−11808). Here, we generalize the approach and provide a comprehensive discussion of how any level in a hierarchical structure contributes to its overall scattering pattern. The results, as well as the general modeling methodology, will be of interest to anyone interested in the quantitative analysis of small-angle scattering data of empty or loaded porous solids and more generally of any type of hierarchical material

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Section: The Case Of Copper-loaded Sba-15mentioning

confidence: 99%

Section: ■ the Case Of Empty Sba-15 Silicamentioning

confidence: 99%

Small-Angle Scattering Analysis of Empty or Loaded Hierarchical Porous Materials

2016

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“…Common capillary-force-directed assembly could be excluded because the self-assembly occurs in aging but not drying process. , There are no any liquid–gas interface and accompanying capillary force existing in aging process. Furthermore, the aged gel does not exhibit apparent shrinkage but just becomes turbid (microstructure shrinkage), which is the typical phenomenon of microsyneresis. − However, microsyneresis is commonly caused by “phase separation in which the polymers cluster together, creating” microscopic “regions of free liquid; the driving force is the greater affinity of the polymer for itself than for the pore liquid” . Here neither inorganic polymer nor solvent is changed.…”

Section: Resultsmentioning

confidence: 99%

“…Thus, it is relatively facile and low-cost for inorganic-based NAs to achieve a high-level SA in comparison with novel metal NPs. However, the microsyneresis was observed rarely in inorganic-based gels but often in organic gels. − Instead of microsyneresis, macroscopic syneresis commonly occurs probably because the inorganic skeletons are usually rigid and inflexible.…”

Section: Introductionmentioning

confidence: 99%

Reaction-Induced Microsyneresis in Oxide-Based Gels: The Assembly of Hierarchical Microsphere Networks

Zhou

et al. 2013

Langmuir

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Rigid and stable networks composed of litchi-shaped microspheres were formed via hierarchical self-assembly (SA) of oxide-based nanoparticles (NPs). The phenomenon of the apparent changes from NPs networks to microspheres networks after the gelation was similar to normal microsyneresis. However, in-situ composition evolution results indicate that the SA is driven by interparticle dehydration, but not affinity difference between the network for itself and for the solvent. In-situ small-angle X-ray scattering (SAXS), UV-vis-NIR, and electric conductivity were used to study the microsyneresis process. To further demonstrate the mechanism, extra complexant was added and successfully restrained the NPs-microsphere transition by inactivating the surface hydroxyl of the NPs. Considering the structural similarity, this work may provide a new approach to control the assemblies of diverse oxide-based NPs.

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“…To a first approximation, the contribution to the SAXS signal of each copolymers subgroup is proportional to the square of β, the number of extra electrons in those groups compared to an identical volume of solvent. − Assuming that any subgroup of the copolymers contributes additively to the volume, it is shown in the Supporting Information that the values of β for the fluorinated blocks are more than 10 times larger than for the PEO blocks for the first three copolymers and about 80% larger for the thermoresponsive copolymer. Therefore, the contribution of the fluorinated sequence is always much larger than the rest of the copolymer, which will only contribute to a few percent of the SAXS signal.…”

Section: Experimental Methodsmentioning

confidence: 99%

Small-Angle X-ray Scattering Insights into the Architecture-Dependent Emulsifying Properties of Amphiphilic Copolymers in Supercritical Carbon Dioxide

et al. 2015

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The supramolecular assembly of a series of copolymers combining poly(ethylene oxide)-rich hydrophilic and fluorinated CO2-philic sequences is analyzed by synchrotron small-angle X-ray scattering (SAXS) in supercritical CO2, as well as in water/CO2 emulsions. These copolymers were designed to have the same molecular weight and composition and to differ only by their macromolecular architecture. The investigated copolymers have random, block, and palm-tree architectures. Besides, thermoresponsive copolymer is also analyzed, having a hydrophilic sequence becoming water-insoluble around 41 °C, i.e., just above the critical point of CO2. At the length scale investigated by SAXS, only the random copolymer appears to self-assemble in pure CO2, in the form of a disordered microgel-like network. The random, block, and thermoresponsive copolymers are all able to stabilize water/CO2 emulsions but not the copolymer with the palm-tree architecture, pointing at the importance of macromolecular architecture for the emulsifying properties. A modeling of the SAXS data shows that the block and the thermoresponsive copolymers form spherical micelle-like structures containing about 70% water and 30% polymer.

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Condensation-Induced Decrease of Small-Angle X-ray Scattering Intensity in Gelling Silica Solutions

Cited by 5 publications

References 24 publications

Small-Angle Scattering Analysis of Empty or Loaded Hierarchical Porous Materials

Small-Angle Scattering Analysis of Empty or Loaded Hierarchical Porous Materials

Reaction-Induced Microsyneresis in Oxide-Based Gels: The Assembly of Hierarchical Microsphere Networks

Small-Angle X-ray Scattering Insights into the Architecture-Dependent Emulsifying Properties of Amphiphilic Copolymers in Supercritical Carbon Dioxide

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