| Self-diffusion of poly(propylene glycol) in nanoporous glasses studied by pulsed field gradient NMR: A study of molecular dynamics and surface interactions. | |
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MedLine Citation:
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PMID: 20831334 Owner: NLM Status: PubMed-not-MEDLINE |
Abstract/OtherAbstract:
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Pulsed field gradient NMR is applied to investigate the self-diffusion of poly(proypylene glycol) in nanoporous glasses (nominal pore sizes of 2.5-7.5 nm). In general, the diffusion is slowed down by the confinement compared to the bulk. For native pore surfaces covered by hydroxyl groups the spin echo attenuation Ψ displays a bimodal behavior versus q(2)t (q-norm of a generalized scattering vector). This was explained assuming spatial regions of different diffusivities in a two-phase model. The slow component is assigned to segments forming a surface layer close to the pore walls in which the segments have a lower mobility than those located in the center of the pores. By variation of observation time it was concluded that time constant for the dynamic exchange of segments between these two regions is around 100 ms at room temperature. For silanized pores, the bimodal behavior in the spin echo attenuation Ψ shows a stretched exponential decay versus q(2)t. The estimated diffusion coefficients decrease strongly with decreasing pore size. The temperature dependence of the diffusion coefficient can be approximated by an Arrhenius law where the activation energy increases with decreasing pore size. The observed pore size dependence for the diffusion of poly(propylene glycol) in silanized nanoporous glasses can be discussed assuming interaction and confining size effects. |
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Authors:
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A Schönhals; F Rittig; J Kärger |
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Publication Detail:
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Type: Journal Article |
Journal Detail:
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Title: The Journal of chemical physics Volume: 133 ISSN: 1089-7690 ISO Abbreviation: J Chem Phys Publication Date: 2010 Sep |
Date Detail:
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Created Date: 2010-09-13 Completed Date: 2011-01-11 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 0375360 Medline TA: J Chem Phys Country: United States |
Other Details:
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Languages: eng Pagination: 094903 Citation Subset: - |
Affiliation:
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BAM Bundesanstalt für Materialforschung und-prüfung, Unter den Eichen 87, 12205 Berlin, Germany. andreas.schoenhals@bam.de |
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