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Pore morphology and interconnectivity in a mesoporous/macroporous polyhedral silica foam material
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.ORCID iD: 0000-0002-0231-3970
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 9, 4827-4832 p.Article in journal (Other academic) Published
Abstract [en]

The pore system of a highly swollen, block-copolymer-templated, polyhedral silica foam material is investigated by a combination of transmission electron microscopy, nitrogen sorption, and NMR cryoporometry. The adsorption-desorption hysteresis and melting-freezing hysteresis data recorded by the respective methods provide pore Volume and access channel sizes that virtually coincide for the two used methods. This provides a consistent picture where polyhedral foam cells of 60-70 nm diameter are interconnected by cylindrical access channels with several characteristic sizes for the latter.

Place, publisher, year, edition, pages
2008. Vol. 24, no 9, 4827-4832 p.
Keyword [en]
nitrogen sorption, porous solids, mercury porosimetry, mesoporous materials, nmr cryoporometry, adsorption branch, size distribution, intrusion, probe, thermoporometry
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-6456DOI: 10.1021/la702318yISI: 000255432000062Scopus ID: 2-s2.0-44249112883OAI: oai:DiVA.org:kth-6456DiVA: diva2:11174
Note
Uppdaterad från manuskript till artikel: 20100927. Tidigare titel: Pore morphology and interconnectivity in a surfactant-templated mesoporous silica material. QC 20100927Available from: 2006-11-29 Created: 2006-11-29 Last updated: 2010-09-27Bibliographically approved
In thesis
1. Phase transitions in porous media studied by NMR
Open this publication in new window or tab >>Phase transitions in porous media studied by NMR
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This Thesis presents studies of phase transitions ocurring in porous media. The investigated phase transitions include melting/crystallization, surface pre-melting and liquid-liquid phase separation of binary mixtures. A combination of NMR techniques, already existing and newly developed and ranging from cryoporometry to elaborate self-diffusion and spin-relaxation experiments, was applied in order to detect and quantify the effect of finite size constraints on those phase transitions. By relating the results to physico-chemical models, the difference in behaviour with respect to that of bulk was exploited and related to pore morphology and surface properties in diverse porous systems.

NMR cryoporometry is based on the detection of the melting/freezing temperature shifts with respect to those in the bulk state to obtain mean pore size and pore size distribution. We extended the size range in which this can be done in porous matrices of both hydrophilic and hydrophobic nature to a 1 μm-600 nm upper limit. This was achieved by introducing two new probe liquids namely octamethylcyclotetrasiloxane (OMCTS) and zinc nitrate hexahydrate Zn(NO)3•H2O.

The thickness of the pre-molten surface layer that appears at the interface of frozen octamethylcyclotetrasiloxane (OMCTS) to the matrix in controlled porous glasses was quantified and modeled including its temperature and wall-curvature dependence. The results reveal that the layer thickness depends logarithmically on the deviation from the pore melting point, while for the largest pore investigated this turns into a power law with the exponent of –1/2. Diverse NMR techniques were used not only to detect solely the surface layer and the evolution of the surface melting, but also to distinguish the latter from the volume melting transition within the pores.

The morphologies of two nanostructured materials, sintered films of TiO2 nanoparticles and a mesoporous foam obtained by surfactant-templated synthesis, were investigated. These two porous matrices have very different structures but fall into the size range accessible by NMR cryopormetry and their characterization plays an important role in their future applications. They were studied by exploiting the difference between melting and freezing temperature shifts ΔTm and ΔTf, respectively, with respect to that of bulk. NMR cryoporometry was shown to be a suitable alternative and an excellent complement to other porosimetry techniques, namely mercury intrusion and gas sorption porosimetries to analyze the pore structure and pore size distribution because of the unique and model-independent access to information about pore shape. By combining NMR cryoporometry with NMR diffusion experiments holds great potential for accessing information about pore interconnectivity.

By diverse NMR techniques we provided experimental evidence that corroborate that liquid-liquid phase separation of a binary mixture imbibed in porous media actually occurs within the individual pores. The size distribution of the phase-separated domains was measured.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. x, 50 p.
Series
Trita-FYK, 0603
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-4197 (URN)987-91-7178-526-8 (ISBN)
Public defence
2006-12-08, Sal D3, KTh, Lindstedtsvägen 5, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20100927Available from: 2006-11-29 Created: 2006-11-29 Last updated: 2010-09-27Bibliographically approved

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