In situ small-angle neutron scattering study of nitrogen adsorption and condensation in mesoporous silica glass CPG-10-75

Hoinkis, E.; Röhl-Kuhn, B.

doi:10.1016/j.jcis.2005.08.044

Cited by 18 publications

(12 citation statements)

References 33 publications

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“…Capillary condensation and evaporation take place gradually. An increase of the pore size for the disordered mesoporous silicas often causes an alteration in the hysteresis loop of type H2 to type H1 for the adsorption isotherm of nitrogen at 77 K, ,, as is the case for the present study. For the CPG sample with the average pore diameter of 13.3 nm, however, no changes in the mechanisms for capillary condensation and for capillary evaporation have been observed by neutron scattering measurements .…”

Section: Resultssupporting

confidence: 64%

Hysteresis Critical Point of Nitrogen in Porous Glass: Occurrence of Sample Spanning Transition in Capillary Condensation

Morishige

2009

Langmuir

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To examine the mechanisms for capillary condensation and for capillary evaporation in porous glass, we measured the hysteresis critical points and desorption scanning curves of nitrogen in four kinds of porous glasses with different pore sizes (Vycor, CPG75A, CPG120A, and CPG170A). The shapes of the hysteresis loop in the adsorption isotherm of nitrogen for the Vycor and the CPG75A changed with temperature, whereas those for the CPG120A and the CPG170A remained almost unchanged with temperature. The hysteresis critical points for the Vycor and the CPG75A fell on the common line observed previously for ordered mesoporous silicas. On the other hand, the hysteresis critical points for the CPG120A and the CPG170A deviated appreciably from the common line. This strongly suggests that capillary evaporation of nitrogen in the interconnected and disordered pores of both the Vycor and the CPG75A follows a cavitation process at least in the vicinity of their hysteresis critical temperatures in the same way as that in the cagelike pores of the ordered silicas, whereas the hysteresis critical points in the CPG120A and the CPG170A have origin different from that in the cagelike pores. The desorption scanning curves for the CPG75A indicated the nonindependence of the porous domains. On the other hand, for both the CPG120A and the CPG170A, we obtained the scanning curves that are expected from the independent domain theory. All these results suggest that sample spanning transitions in capillary condensation and evaporation take place inside the interconnected pores of both the CPG120A and the CPG170A.

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Section: Resultssupporting

confidence: 64%

Hysteresis Critical Point of Nitrogen in Porous Glass: Occurrence of Sample Spanning Transition in Capillary Condensation

Morishige

2009

Langmuir

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“…The second mechanism is related to the differences in the microscopic distribution of the liquid phase within the porous solid. [192][193][194] In our case, the PFG NMR data indicate that, on the micrometer length scale, such a distribution is homogeneous. The origin of different distributions on adsorption and desorption is, thus, attributed to an interplay between cavitation and pore-blocking effects, leading to the formation of more extended mesoscale regions of the capillary-condensed and gaseous phase during adsorption.…”

Section: Phase State and Transportsupporting

confidence: 50%

Correlating phase behaviour and diffusion in mesopores: perspectives revealed by pulsed field gradient NMR

Valiullin

Kärger

Gläser

2009

Phys. Chem. Chem. Phys.

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Porous solids represent an important class of materials widely used in different applications in the field of chemical engineering. In particular, mesoporous hosts attract special attention due to their fascinating match of transport, geometrical and chemical properties. Not only a very high specific surface area, accessible for adsorption and heterogeneous catalysis, but also their efficient transport properties are the key factors determining optimal use of these materials. Therefore, a fundamental understanding of the correlations between the phase state of confined fluids, their transport properties and the geometrical features of confinement are of particular importance. Among the different analytical techniques, nuclear magnetic resonance (NMR) is especially suited to cover various crucial aspects of the highlighted issues. In this work, we provide a short overview of recent advances related to the interrelations of phase behaviour and diffusion in mesoporous materials studied using various NMR techniques.

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“…Several suggestions had already been made with regards to the initial step of self‐ assembly process, such as the coating of rodlike micelles, or initial formation of a gel phase in analogy to the formation of polyelectrolyte‐surfactant complexes 9–11. Time resolved in situ study with fluorescence probing, SAXS/SAXRD/SANS, NMR, and TEM were also used in this investigation so as to give some experimental verification on the above‐mentioned suppositions 12–15. Subsequently, Flodström et al16 explained the phase transformation of P123‐TEOS through the analysis of SAXRD reflection.…”

Section: Introductionmentioning

confidence: 93%

In situ SAXRD study of sol–gel induced well‐ordered mesoporous bioglasses for drug delivery

Loo

Chen

Boey

et al. 2007

J Biomedical Materials Res

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In this work, two systems of mesoporous bioglasses (MBGs) were sol-gel derived using block copolymer pluronic F127 and P123, respectively, as templates. A two-dimensional hexagonal (P6mm) mesoporous structure was obtained for the two systems, with d-spacing in (100) reflection of 8.49 nm for P123-templated MBG (P123-MBG) and 10.26 nm for F127-templated MBG (F127-MBG). The phase transformation behavior for the systems was elucidated using an in situ synchrotron small angle X-ray diffraction approach, with the corresponding mechanisms proposed. It was indicated that both systems go through a complicated phase transformation, from a disordered to a finely ordered hexagonal structure during the self-evaporation process. The surfactants not only acted as templates for the ordered structure, but also enhanced the rigidity of Si-O network, which prevented disruption to the ordered Si-O arrangement by the Ca(2+) and P-O group. In vitro bioactivity study showed similar bioactivity for both the P123-MBG and F127-MBG systems. Drug loading and release studies using a model metoclopramide drug showed that both MBGs presented better loading and release compared to normal bioglass (BG). The significantly higher loading and better sustained release for P123-MBG, compared to F127-MBG, is attributed to its higher pore volume and surface area.

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In situ small-angle neutron scattering study of nitrogen adsorption and condensation in mesoporous silica glass CPG-10-75

Cited by 18 publications

References 33 publications

Hysteresis Critical Point of Nitrogen in Porous Glass: Occurrence of Sample Spanning Transition in Capillary Condensation

Hysteresis Critical Point of Nitrogen in Porous Glass: Occurrence of Sample Spanning Transition in Capillary Condensation

Correlating phase behaviour and diffusion in mesopores: perspectives revealed by pulsed field gradient NMR

In situ SAXRD study of sol–gel induced well‐ordered mesoporous bioglasses for drug delivery

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