buletinul institutului politehnic din iaşi - Universitatea Tehnică ...

60 Răzvan Florin Barzic et al.
Current interest to improve the thermal conductivity of polymers is focused on
the selective addition of nanofillers with high thermal conductivity. Unusually
high thermal conductivity makes carbon nanotubes (CNT) the best promising
candidate material for thermally conductive composites (Han & Fina, 2011).
For an enhanced thermal conductivity the CNT must be well dispersed and
oriented in the polymer matrix (Ke et al., 2007 and Riggs et al., 2000).
The aim of the present study is to prepare some nanocomposites from
commercial polymer (polystyrene) and CNT, the latter being dispersed by
ultrasonication. The orientation of the used nanofillers was achieved by a new
method which implies a shear field. The morphology of resulted
nanocomposites is evaluated by atomic force microscopy. Thermal conductivity
of these materials is estimated by considering it as an additive function of the
PS and CNT compositions. All these aspects are presented in the context of the
current state of research on thermal and morphological characterization of
polymer composites in heat engineering-oriented applications, marking the own
research and future directions.
2. Experimental
2.1. Materials
Polystyrene (PS) was purchased from Sigma Aldrich having a molecular
weight of 40 000 g/mol. Also, carbon nanotubes (CNT) were achieved from SC
ICEFS COM SRL Savinesti having a diameter of 8…15 nm. To get a better
dispersion and orientation of carbon nanotubes into the matrix of polystyrene
(PS) a new method has been employed, which consists in shearing the
composite starting from the solution phase. For this purpose, we used a solvent
with high diffusion rate, i.e. methylene chloride, to maintain the organization
imposed shear.
Thus, the solution is deposited onto a device similar to that illustrated in
Fig. 1, which has a moving blade, inducing shear controlled orientation of
macromolecular chains and implicitly the carbon nanotubes. To investigate to
what extent this technique leads to the desired result morphological studies were
made on the nanocomposite films prepared as described previously.
2.2. Characterization
Atomic force microscopy (AFM) data were recorded with a camera Pro-
M SPM Solver tool. Peak use is the type NSG10/Au Silicon, having a radius of
curvature of 10 nm and an average oscillation frequency of 255 kHz. The
images were scanned in semi-contact, their resolution is 256 × 256.
The glass transition temperature of PS was determined with a Mettler
differential scanning calorimeter.