Porosity of silica Stöber particles determined by spin-echo small angle neutron scattering

Parnell, Steven R.; Washington, A. L.; Parnell, Andrew J.; Walsh, A.; Dalgliesh, Robert M.; Li, F.; Hamilton, W. A.; Prévost, Sylvain; Fairclough, J. Patrick A.; Pynn, R.

doi:10.1039/c5sm02772a

Cited by 40 publications

(34 citation statements)

References 30 publications

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“…0.23 cm 3 /g from CO 2 isotherms 54 and 0.32 cm 3 /g from spin-echo small-angle neutron scattering. 77 Such large micropore volumes seems to be overestimated, since they 16 would correspond to spheres with an empty volume of > 40% (mass density < 1.3 g/ cm 3 ), a fact hardly reconcilable with the densities usually measured (> 1.8 g/ cm 3 ). Also, by considering the porosity effect on the mechanical robustness, 78 the high Young modulus of Stöber spheres (about half of the silica bulk value), 50 agrees with the porosity we estimate, while a drastic decrease in a factor of ten would be expected for 40% porosity.…”

Section: Water Adsorption Isothermsmentioning

confidence: 94%

Direct Measurement of Microporosity and Molecular Accessibility in Stöber Spheres by Adsorption Isotherms

et al. 2018

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The microporous nature of monodisperse Stöber silica spheres is demonstrated in the literature, although usually via indirect evidence. Contradictorily, there also exist numerous reports of nonporosity based on conventional N 2 adsorption isotherms, leading to a confusing scenario and questioning the evaluation methodology. Thus, there is the strong need of straight measure of microporosity in Stöber spheres, at best by available adsorption techniques, which must be further directly confronted with the standard nitrogen method. Here, for the first time, microporosity detection by N 2 and CO 2 adsorption are compared in Stöber spheres. We demonstrate that CO 2 isotherms at 273 K allows direct detection and quantification of the microporosity (about 0.1 cm 3 /g in our samples), while N 2 at 77 K cannot probe adequately the internal volume. We also show that a large amount of water fills the micropores under usual ambient conditions, also revealing the presence of small mesoporosity. Thus, the porous nature of Stöber spheres is investigated by a simple combination of adsorption isotherms, and the different accessibility of N 2 , CO 2 and H 2 O molecules are discussed. We emphasize the inadequacy of standard N 2 isotherms for micropore detection in Stöber silica, as the access of nitrogen molecules at cryogenic temperatures is kinetically restricted and may lead to erroneous 2 conclusions. Instead, we propose CO 2 isotherms as a simple and direct means for evaluation of microporosity.

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Section: Water Adsorption Isothermsmentioning

confidence: 94%

Direct Measurement of Microporosity and Molecular Accessibility in Stöber Spheres by Adsorption Isotherms

et al. 2018

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“…The 0.7% discrepancy between n 0 and the refractive index of fused silica may be ascribed in part to the well-documented difference in density between emulsion-polymerized silica and fused silica. [28][29][30][31] The discrepancy also is likely to depend on the molecules' sizes and their affinity for silica, both of which affect their ability to access the particles' pores. Pores that are inaccessible to the high-index species in solution will tend to reduce a sphere's apparent porosity.…”

Section: Effective-sphere Characterization Of Mesoporous Silica Spheresmentioning

confidence: 99%

The role of the medium in the effective-sphere interpretation of holographic particle characterization data

et al. 2020

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“…Spin-echo small-angle neutron-scattering measurements on particles synthesized via the Stöber have found an open-pore volume fraction of 32% and an inaccessiblepore volume fraction of 10% for particles with radius of approximately 80 nm [42]. It is distinctly possible that MSs in solution absorb a nontrivial amount of water or other solvent, and that under low-to high-vacuum conditions, the liquid is removed, effectively lowering the mass and density.…”

Section: Effectmentioning

confidence: 99%

Precision Mass and Density Measurement of Individual Optically Levitated Microspheres

et al. 2019

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We report an in situ mass measurement of approximately-4.7-µm-diameter, optically levitated microspheres with an electrostatic co-levitation technique. The mass of a trapped, charged microsphere is measured by holding its axial (vertical) position fixed with an optical feedback force, under the influence of a known electrostatic force. A mass measurement with 1.8% systematic uncertainty is obtained by extrapolating to the electrostatic force required to support the microsphere against gravity in the absence of optical power. In three cases, the microspheres are recovered from the trap on a polymer-coated silicon beam and imaged with an electron microscope to measure their radii. The simultaneous precision characterization of the mass and radius of individual microspheres implies a density of 1.55 ± 0.08 g/cm 3 . The ability to recover individual microspheres from an optical trap opens the door to further diagnostics.

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Porosity of silica Stöber particles determined by spin-echo small angle neutron scattering

Cited by 40 publications

References 30 publications

Direct Measurement of Microporosity and Molecular Accessibility in Stöber Spheres by Adsorption Isotherms

Direct Measurement of Microporosity and Molecular Accessibility in Stöber Spheres by Adsorption Isotherms

The role of the medium in the effective-sphere interpretation of holographic particle characterization data

Precision Mass and Density Measurement of Individual Optically Levitated Microspheres

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