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Thermal conductivity, heat capacity, and cross-linking of polyisoprene/single-wall carbon nanotube composites under high pressure
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
2009 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 42, no 23, 9295-9301 p.Article in journal (Refereed) Published
Abstract [en]

Polyisoprene (PI)/single-wall carbon nanotube (SWCNT) composites and pure PI have been cross-linked by high-pressure treatment to yield densified elastomeric states. Simultaneously, the SWCNT and cross-linked-induced changes of the thermal conductivity, heat capacity per unit volume, and glass transition were investigated by in situ measurements. The thermal conductivity of both the elastomeric and liquid PI improves ≈120% by the addition of 5 wt % SWCNT filler. The SWCNT filler (5 wt %) increases the glass-transition temperature of liquid PI by ≈7 K and that of the elastomeric state by as much as 12 K, which is due to a filler-induced increase in the cross-link density. Moreover, the 5 wt% filler yields a heat capacity decrease by ≈30% in both the glassy and liquid/elastomeric states, which indicates that SWCNTs cause a remarkably large reduction of both the vibrational and configurational heat capacity of PI. Finally, the consequences of high-pressure densification and the possibilities this provides to help elucidating the nature of the heat conduction in polymer/carbon nanotube composites are discussed.

Place, publisher, year, edition, pages
American Chemical Society , 2009. Vol. 42, no 23, 9295-9301 p.
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-30449DOI: 10.1021/ma902122uOAI: oai:DiVA.org:umu-30449DiVA: diva2:283409
Available from: 2009-12-25 Created: 2009-12-25 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Thermal and mechanical studies of carbon nanotube-polymer composites synthesized at high pressure and high temperature
Open this publication in new window or tab >>Thermal and mechanical studies of carbon nanotube-polymer composites synthesized at high pressure and high temperature
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, thermal and mechanical properties of polymers and carbon nanotubes-polymer composites, which were modified and studied under high pressure, are presented. The results concern the thermal conductivity κ and heat capacity per unit volume ρcp of pure polymers: polyisoprene (PI), polybutadiene (PB), and nylon-6, and their multi-wall and single-wall carbon nanotube (MWCNT and SWCNT) composites both before (untreated) and after high pressure treatments. As shown here, a suitable high pressure high temperature (HP&HT) treatment induces either cross-links in the polymers (PI and PB), i.e. transforms these into elastomers, or increases the crystallinity (nylon-6).

The experiments were done, in situ, in the temperature range 100-520 K for pressures up to 1.5 GPa, and the results show that cross-linking under high pressure can be monitored in data for κ and ρcp. Moreover, κ for a well cross-linked (ebonite-like) polymer near ambient conditions can be up to 50% higher than the untreated states, whereas ρcp becomes similar as the glassy state of the untreated polymer. The glass transition of the cross-linked states becomes broader and shifts to higher temperatures with increasing degree of cross-linking. In the case of nylon-6, the HP&HT treatment causes microstructural changes, viz. increased crystallinity and crystals with a preferred orientation and increased size, which enhances κ and improves the thermal stability.

The thermal property studies of the CNT polymer composite show that k of the composites increases significantly, e.g. 120% for 5wt% SWCNTs in PI, which is attributed to the very high k of CNTs. Moreover, MWCNTs also improve k, but not as much as SWCNTs. This is accounted for by their lower aspect ratio (length/diameter), whereas their lower k is less important. Adding CNTs normally raise the glass transition temperatures of the polymers. More specifically, SWCNTs in PB raise the glass transition temperature slightly more than MWCNTs and, in particular, under the most densified conditions and for a high molecular weight PB, which may be due to more favorable conditions for coating/wrapping of the CNTs.

The mechanical studies of the HP&HT treated polymers and composites show that CNTs strongly enhances the tensile strength and Young’s modulus, e.g. 5 wt% SWCNT in PI synthesized at 1 GPa and 513 K showed 2 times higher tensile strength and 2.3 times higher Young’s modulus than that of similarly treated pure PI. The results indicate that the treatment improves the poor interfacial contact between the CNTs and polymer, which is one of the obstacles for achieving stronger CNT composites

Place, publisher, year, edition, pages
Umeå: Institutionen för fysik, Umeå Universitet, 2011. 52 p.
Identifiers
urn:nbn:se:umu:diva-43477 (URN)978-91-7459-223-8 (ISBN)
Public defence
2011-06-03, Naturvetarhuset, N300, Umeå universitet, Umeå, 10:15 (English)
Opponent
Supervisors
Available from: 2011-05-06 Created: 2011-05-02 Last updated: 2011-05-04Bibliographically approved
2. Studies of novel phases and states produced by means of high pressure: Polymer and polymer based carbon nanocomposites
Open this publication in new window or tab >>Studies of novel phases and states produced by means of high pressure: Polymer and polymer based carbon nanocomposites
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Umeå: Institutionen för fysik, Umeå universitet, 2011
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:umu:diva-49817 (URN)978-91-7459-315-0 (ISBN)
Public defence
2011-12-15, Naturvetarhuset, N200, Umeå universitet, Umeå, 13:30
Opponent
Supervisors
Available from: 2011-11-24 Created: 2011-11-18 Last updated: 2011-11-21Bibliographically approved

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