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Name (Title):
Bando Yoshio (PI, Chief Operating Officer and NIMS Fellow)
Affiliation:
International Center for Materials Nanoarchitectonics
(MANA), NIMS
Address:
1-1 Namiki, Tsukuba. Ibaraki 305-0044, Japan
Email: Bando.Yoshio@nims.go.jp
Home Page: http://www.nims.go.jp/mana/members/principal_investigator/y_bando/index.html
Presentation Title:
Towards thermo-conductive electrically insulating polymeric composites using BN nanotubes as
fillers
Abstract:
Boron nitride nanotubes (BNNTs) are electrically insulating counterparts of CNTs due to a
constant and wide band gap of ~5.5 eV. Similar to CNTs they possess high thermal conductivity.
Theoretical predictions have indicated that the thermal conductivity of a single-walled BNNT may
even surpass that of CNT (3000 W/mK). Experimentally, it was found that the thermal
conductivity of nanotubes decreased with increasing diameters. The BNNTs with diameters of ~40
nm may have thermal conductivity of 200-300 W/mK along the axis direction, which is notably
higher than the numbers for the standard AlN, Al2O3 and BN powders. A principal advantage of
one-dimensional nanosize filler utilization can be simply explained as follows. As shown in Figure
1, a conventional BN powder can be considered as a small h-BN crystal which possesses high
thermal conductivity in the (002) plane, but a poor thermal transfer along the [002] direction. This
gives an overall thermal conductivity of ~30 W/mK even though the thermal conductivity inside
the (002) plane can be much higher. However, a BN tubular structure makes it is possible to solely
utilize high thermal conductivity of the (002) planes while minimizing the effect of other crystal
faces especially in well-aligned tubular layers. Moreover, BNNTs are chemical inert, oxidationproof
and structurally stable. These features make a BNNT a highly attractive material for
increasing thermal conductivity and reducing CTE of advanced insulating polymers.
Utilizing boron nitride nanotubes (BNNTs) as fillers polymethyl methacrylate (PMMA),
polystyrene (PS), polyvinyl butyral (PVB) and polyethylene vinyl alcohol (PEVA) composites were
fabricated and their thermal, electrical and mechanical properties were evaluated. More than 20-fold
thermal conductivity improvement in BNNT-containing polymers was obtained (Table I), and such
composites keep good electrical insulation. The coefficient of thermal expansion (CTE) of BNNT
loaded polymers was dramatically reduced due to interactions between polymer chains and the
nanotubes. Moreover, the composites possess good mechanical properties, as revealed by micro-
Vickers hardness tests. This detailed study indicates that BNNTs are very promising nanofillers for
polymeric composites which allow one to simultaneously achieve high thermal conductivity, low
CTE and high electrical resistance required for novel and efficient heat releasing materials.
Figure 1. Schematics displaying the anisotropy of thermal
conductivity in micro-sized BN particles and BNNTs.
References :
1. C. Y. Zhi, Y. Bando et al, J. Mater. Chem. 18, 3900 (2008)
2. C. Y. Zhi, Y. Bando et al, Adv. Func. Mater. In press (2009)
Poster Session PM-1
Table I. Thermal conductivity values of PVB, PS, PMMA,
PEVA and their BNNT-containing composites.
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