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Charged Particle Transport: As Information Source about Ion Conductors, Dielectric Materials, and Drug Delivery Systems
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Materials Science.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis treats charged particle transport, mostly in solid materials but also, to some extent, in aqueous media. Three major types of materials have been investigated; dielectric materials, ion conductors, and drug-delivery systems.

The frequency-dependent dielectric permittivity of sputtered amorphous thin film tantalum oxide (Ta2O5) has been determined by using impedance spectroscopy. A new interpolation formula has been derived, that interpolates between the two power-law regions at low and high frequencies usually observed in the dielectric spectrum. This formula is based on a regular-singular-point (RSP) analysis of the conduction process, and the power-laws in the dielectric spectrum are interpreted in terms of RSPs of the underlying rate equation for the corresponding polarization-current response function.

Lithium transport properties of Ta2O5 have been analyzed by using the galvanostatic intermittent titration technique and by isothermal transient ionic current measurements. Chemical and component diffusion coefficients for intercalated lithium have been extracted. Moreover, the ion conduction process has been analyzed theoretically, and expressions for transient ionic currents derived, both for single ion-conducting layers and for three-layered structures of ion conductors.

Electrical measurement techniques have also been applied to pharmaceutical systems. The alternating ionic current technique has been developed as a tool for determining the release of electrically charged drug substances in aqueous media. Tablets made of agglomerated micronized cellulose have been investigated, and sodium chloride has been used as a model drug. An attempt has been made to describe the combined drug dissolution and drug release processes in mathematical terms.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2002. , p. 82
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 725
Keywords [en]
Materials science
Keywords [sv]
Materialvetenskap
National Category
Materials Engineering
Research subject
Engineering Science
Identifiers
URN: urn:nbn:se:uu:diva-2103ISBN: 91-554-5347-3 (print)OAI: oai:DiVA.org:uu-2103DiVA, id: diva2:161760
Public defence
2002-06-07, the Hägg Lecture Hall at the Ångström Laboratory, Uppsala, 09:30
Opponent
Available from: 2002-05-15 Created: 2002-05-15Bibliographically approved
List of papers
1. Li conduction in sputtered amorphous Ta2O5
Open this publication in new window or tab >>Li conduction in sputtered amorphous Ta2O5
2001 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 148, no 5, p. A418-A421Article in journal (Refereed) Published
Abstract [en]

Electron and Li ion conducting properties of room temperature sputtered amorphous tantalum oxide (a-Ta2O5) films were studied in order to evaluate the feasibility of using a-Ta2O5 in electrochromic device applications. The films were investigated using the galvanostatic intermittent titration technique, impedance spectroscopy, and isothermal transient ionic current measurements. It was found that the a-Ta2O5 met two out of three requirements posed on a Li ion conductor in a WO3 based electrochromic device. There was a negligible intercalation in the potential window used in WO3-based electrochromic devices (above 2.4-2.5 V vs. Li/Li+). Furthermore, in this potential region, the chemical diffusion coefficient for Li was larger than the corresponding quantity in WO3. However, there was a nonzero electron conductivity in the a-Ta2O5 films, not observed in the chemical vapor deposition-made β-Ta2O5 investigated earlier. Still, the ionic conductivity was approximately one order of magnitude larger than the electronic one.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-89902 (URN)10.1149/1.1359196 (DOI)2-s2.0-0009639725 (Scopus ID)
Available from: 2002-05-15 Created: 2002-05-15 Last updated: 2017-12-14Bibliographically approved
2. Dielectric and Li transport properties of electron conducting and non-conducting sputtered amorphous Ta2O5 films
Open this publication in new window or tab >>Dielectric and Li transport properties of electron conducting and non-conducting sputtered amorphous Ta2O5 films
Show others...
2001 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 46, no 13-14, p. 2041-2046Article in journal (Refereed) Published
Abstract [en]

Two types of sputtered thin film amorphous tantalum oxide (Ta2O5) were studied: one electron conducting Ta2O5 (ec-Ta2O5) and the other non-conducting Ta2O5 (nc-Ta2O5). The as-deposited films were characterized by impedance spectroscopy (IS) and isothermal transient ionic current (ITIC) measurements. From IS, the dc conductivity 2×10−14 S/cm was obtained for the ec-Ta2O5 film at an applied ac potential of 50 mV whereas a value ≤1×10−17 S/cm was obtained for the nc-Ta2O5 film. Li conducting properties were studied using the galvanostatic intermittent titration technique and ITIC measurements on the intercalated samples. Despite the very dissimilar dc conductivities of the as-deposited films, the two Ta2O5 samples showed surprisingly similar Li ion conducting properties for small Li/Ta2O5 ratios. The Li ion mobility was in the range 1.1×10−9–3.0×10−9 cm2/V s for both films. However, the Li storage behaviour as well as the chemical diffusion coefficient differed. For the nc-Ta2O5 film a plateau was observed in the equilibrium potential vs. composition curve for Li/Ta2O5 ratios between 7×10−5 and 2×10−3. This plateau was likely to have been caused by attractive interactions between the intercalated ions, possibly large enough to cause phase separation. The attractive interactions were shown to suppress the chemical diffusion coefficient in this composition range.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-89903 (URN)10.1016/S0013-4686(01)00412-1 (DOI)
Available from: 2002-05-15 Created: 2002-05-15 Last updated: 2017-12-14Bibliographically approved
3. Dielectric study of thin films of Ta2O5 and ZrO2
Open this publication in new window or tab >>Dielectric study of thin films of Ta2O5 and ZrO2
Show others...
2001 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 8, no 4, p. 648-651Article in journal (Refereed) Published
Abstract [en]

Electronic conduction in sputtered Ta2O5 and ZrO2 thin films have been studied using impedance spectroscopy, isothermal transient ionic current, and current-voltage measurements. The dielectric properties of Ta2O5 were shown to be sensitively dependent on deposition parameters with two different frequency responses: a flat loss behavior with very low DC conductivity, or a relaxation peak together with a somewhat higher DC conductivity. ZrO2 has different dielectric properties when fresh, i.e. newly deposited, or aged. A fresh sample arbitrarily can show two different behaviors, consisting of a DC conductivity with a relaxation peak superimposed on it. The DC conductivity shows either of two different values. The aged sample has a lower permittivity and DC conductivity, and the relaxation peak is found at much lower frequencies. Fresh samples of ZrO2 also show switching behavior

National Category
Medical and Health Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-89904 (URN)10.1109/94.946718 (DOI)
Available from: 2002-05-15 Created: 2002-05-15 Last updated: 2017-12-14Bibliographically approved
4. The dielectric response function determined by regular-singular-point analysis
Open this publication in new window or tab >>The dielectric response function determined by regular-singular-point analysis
In: Phys. Rev. BArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-89905 (URN)
Available from: 2002-05-15 Created: 2002-05-15Bibliographically approved
5. Theoretical derivation of the isothermal transient ionic current in an ion conductor: Migration, diffusion, and space-charge effects
Open this publication in new window or tab >>Theoretical derivation of the isothermal transient ionic current in an ion conductor: Migration, diffusion, and space-charge effects
2001 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 90, no 11, p. 5570-5575Article in journal (Refereed) Published
Abstract [en]

The Green’s function technique was used to determine the isothermal transient ionic current (ITIC) caused by the application of a constant potential across an ion conductor which initially contained the ions under consideration. The analysis included migration, diffusion, and space-charge effects as contributions to the ionic motion. Furthermore, the relative importance of diffusion and space-charge effects as currentlimiters was investigated. It was found that ion concentrations as low as ∼1016–1017 cm−3 are sufficient to make space-charge effects the dominant contribution to the decay of the ITIC at low applied electric fields(∼104 V/cm). Hence such effects should be taken into consideration when the ITIC method is used to determine conduction parameters.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-89906 (URN)10.1063/1.1412585 (DOI)
Available from: 2002-05-15 Created: 2002-05-15 Last updated: 2017-12-14Bibliographically approved
6. Characterization of solid-state ion-shuttling devices by isothermal transient ionic current measurements
Open this publication in new window or tab >>Characterization of solid-state ion-shuttling devices by isothermal transient ionic current measurements
In: Phys. Rev. BArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-89907 (URN)
Available from: 2002-05-15 Created: 2002-05-15Bibliographically approved
7. A new method for characterizing the release of drugs from tablets in low liquid surroundings
Open this publication in new window or tab >>A new method for characterizing the release of drugs from tablets in low liquid surroundings
2002 (English)In: Journal of Pharmaceutical Sciences, ISSN 0022-3549, E-ISSN 1520-6017, Vol. 91, no 3, p. 776-784Article in journal (Refereed) Published
Abstract [en]

The purpose of this article is to introduce a method capable of determining early drug dissolution in small amounts of liquid. The method is based on the measurement of the alternating ionic current through a cell containing the dissolution medium and the substance to be dissolved. Both the initial and more prolonged absorption of liquid into tablets can also be determined by using the same technique. The method has been tested on two tablet formulations containing agglomerated micronized cellulose and NaCl as a model drug. Release of NaCl was delayed from both formulations; the extent of the delay was strongly formulation-dependent only when the surrounding liquid was in short supply. This finding shows that new drug dissolution phenomena may be encountered in small liquid volumes; these phenomena would not have been seen with the large volume methods normally used in in vitro dissolution tests. Hence, for formulations intended for sublingual, buccal, or rectal administration, i.e., in areas where liquid is scarce, in vitro dissolution tests should be performed in small volumes of dissolution medium.

National Category
Medical and Health Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-89908 (URN)10.1002/jps.10077 (DOI)11920763 (PubMedID)
Available from: 2002-05-15 Created: 2002-05-15 Last updated: 2017-12-14Bibliographically approved
8. Drug release modeled by dissolution, diffusion, and immobilization
Open this publication in new window or tab >>Drug release modeled by dissolution, diffusion, and immobilization
2003 (English)In: International Journal of Pharmaceutics, ISSN 0378-5173, E-ISSN 1873-3476, Vol. 250, no 1, p. 137-145Article in journal (Refereed) Published
Abstract [en]

This article presents a novel drug release model that combines drug dissolution, diffusion, and immobilization caused by adsorption of the drug to the tablet constituents. Drug dissolution is described by the well-known Noyes–Whitney equation and drug adsorption by a Langmuir–Freundlich adsorption isotherm, and these two processes are included as source and sink terms in the diffusion equation. The model is applicable to tablets that disintegrate into a number of approximately spherical fragments. In order to simplify the analysis it is assumed that liquid absorption, matrix swelling, and tablet disintegration are much faster than drug dissolution and subsequent drug release. The resulting model is shown to yield release characteristics in good agreement with those observed experimentally.

National Category
Medical and Health Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-89909 (URN)10.1016/S0378-5173(02)00539-2 (DOI)
Available from: 2002-05-15 Created: 2002-05-15 Last updated: 2017-12-14Bibliographically approved

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