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Generalized regular singular-point description of low-frequency dielectric responses
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences.
2004 In: Phys. Rev. B, Vol. 70, 012506:1-4 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2004. Vol. 70, 012506:1-4 p.
URN: urn:nbn:se:uu:diva-94367OAI: oai:DiVA.org:uu-94367DiVA: diva2:168193
Available from: 2006-04-21 Created: 2006-04-21Bibliographically approved
In thesis
1. Water-Induced Charge Transport in Microcrystalline Cellulose
Open this publication in new window or tab >>Water-Induced Charge Transport in Microcrystalline Cellulose
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Vatteninducerad laddningstransport i mikrokristallin cellulosa
Abstract [en]

Microcrystalline cellulose (MCC) is the most frequently used excipient for direct compaction of tablets within the pharmaceutical industry. It has earlier been indicated that the interactions between the hydration shell – surrounding the drug molecules in an MCC tablet – and the cellulose regulate the speed of the drug release process. These interactions, and the charge transport governed by moisture, are therefore important to analyze and understand to be able to tailor make new functional drug delivery systems.

In this thesis the physical parameters affecting the water-induced ionic transport have been studied with impedance spectroscopy, transient current measurements, nitrogen adsorption and scanning electron microscopy. Dielectric relaxation processes, pertaining to other processes, have also been assessed and analysed, and a generalized regular singular point model has been shown to be able to describe all features of the dielectric spectrum.

It has been shown that the ionic charge transport mechanism in humid MCC most likely is governed by two parallel processes: One involving water constituent ions diffusing between adjacent lowest energy sites (free OH- groups) in disordered regions of the cellulose and the other caused by impurity ions, such as Na+, and protons or H3O+ ions, jumping between neighboring cellulose OH- groups to which primary water molecules are attached. At relative humidities of ~ 37 % (representing monolayer coverage) and higher, the latter process is totally dominating the charge transport.

At a given moisture content, there are two parameters determining the magnitude of the water-induced ionic conductivity in MCC: The connectedness of the interparticulate bonds and the connectedness of pores with a diameter in the 5-20 nm size range.

The presented findings emphasize the importance of analysing and being able to control the nanostructure of a pharmaceutical cellulose-based system in order to tailor the drug transport properties. The presented results should also be significant for other areas where cellulose-water interactions are of key issue; such as for paper and sanitary product research and for food industries using cellulose-based gels.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 53 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 170
Materials science, Materialvetenskap
urn:nbn:se:uu:diva-6815 (URN)91-554-6541-2 (ISBN)
Public defence
2006-05-12, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30
Available from: 2006-04-21 Created: 2006-04-21Bibliographically approved

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