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Fabrication of polypyrrole-polyimide core-shell nanoparticles and

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Fabrication of polypyrrole-polyimide core-shell nanoparticles and Powered By Docstoc
					      Fabrication of polypyrrole-polyimide core-shell nanoparticles and
                       application to high-K materials

     Hyun-Yool Woo, Mincheol Chang, Jae Buem Oh, Hyun Min Jung, Jae Heung Lee,
                                 Jong Chan Won*

                             P.O. Box 107, Sinseongno 19
                 KRICT(Korea Research Institute of Chemical Technology)
                          Yuseong, Daejeon 305-600, Korea
                                  (jcwon@krict.re.kr)

Introduction
Recently, Polypyrrole(PPy) is estimated as one of the most important conducting polymers
due to its high conductivity and a large variety of application1-3. So many approaches such as
loading of PPy into polymer matrix for increased conductivity and for high capacitance have
been attempted. However, conducting polymers have some of the drawbacks to the
application such as their poor mechanical properties, low environmental stability and poor
processability. To overcome these drawbacks, various research groups studied by formulating
composites of the conducting polymer and organic/inorganic materials4-6. Although these
various efforts have produced high capacitance materials, they have high conductivity which
is major problem for use as high dielectric insulators and capacitors.
Because of the needs of high k dielectric and insulator materials, we devised a new high k
dielectric material using a core-shell nanoparticles structure with conducting polymer as the
high capacitance core, and polyimide as the shell. These core-shell particles are expected a
low conductivity and dissipation factor because PI shells take a role of insulating layer and
prevent from physical contact of PPy particles to restrict the electron transfer between PPy
nanoparticles. These fabricated PPy@PI core-shell nanoparticles can be applied to all-
polymer nanocomposites for high dielectric materials.

Experimental
Fabrication of PPy:
PPy nanoparticles were obtained the following typical synthesis; As a surfactant, DTAB was
added to mixture containing DI-water and decyl alcohol at 3oC. And then pyrrole was added
to the surfactant solution, and ferric chloride was introduced into the surfactant solution. The
chemical oxidation of the pyrrole monomer was conducted for 2 h at 3oC. The fabricated
product was washed with ethanol to remove the excess surfactant and dried at room
temperature7.
Fabrication of PI-coated PPy nanoparticles:
Polyamic acid(PAA) are added to PPy solution. And then these solutions were well dispersed
via ultrasonication, PPy/PAA solution was dropped into the non-solvent under the vigorous
stirring. After 6h, PAA on the PPy core particles were imidized by chemical imidization
which proceeded with acetic anhydride and pyridine. The resulting product was washed and
dried at room temperature. The characterizations of resulting particles were carried out by
some techniques such as SEM, TEM, FT-IR, UV-Vis, zeta-potential and dielectric constant
measurement.
                 Figure 1: Schematic illustration of PI coated PPy nanoparticle fabrication

Results and Discussion
        PPy@PI core-shell nanoparticles were successfully fabricated through the interfacial
precipitation method. The morphology of the core-shell particle structure was confirmed by
the SEM and TEM. The diameter of PPy@PI core-shell nanoparticles were between 150 and
200 nm and the morphology of resulting product had a spherical shape. Its structural change
was confirmed by IR and UV-visible spectra. It indicates that considerable imidization has
occurred by showing the changes in the characteristic PAA peaks at: 1410 cm-1, 1513 cm-1
(1560 cm-1), 1660 cm-1 (1680 cm-1) and corresponding increase in the imide peaks at: 1770
cm-1, 1380 cm-1 and 720 cm-1, respectively.
        The dielectric constant values of the resulting product were measured at 10KHz. The
prepared PPy@PI core-shell particles showed improved k values from 37 (PPy@PI=3:7) to
1545 (PPy@PI=7:3) with the increase of PPy loading contents. Moreover, the relatively low
conductivity value (< 10-7 S/cm) and dielectric loss tangent of the PPy@PI particles were
obtained. These results are suggesting that fabricated core-shell nanoparticles are able to be
applicable as effective high k and insulating materials.

Conclusions
        Polypyrrole (PPy)-polyimide (PI) core-shell nanoparticles (150 ~ 200 nm in diameter)
have been successfully prepared using PPy nanoparticles (~ 100 nm in diameter); PPy
nanoparticles were encapsulated with polyamic acid (PAA) owing to their electrostatic
attraction. Thereafter, coated PAA on the PPy core was imidized by chemical imidization.
PPy@PI core-shell nanoparticles were revealed high k dielectric property because its
structure consists of conducting polymer core as the high capacitance and polyimide shell as
insulator. As-prepared nanomaterials can be applied to all-polymer nanocomposites for high
dielectric performance as well dispersed fillers below percolative composition.

References
1
  Ramanavicius, A; Ramanaviciene, A; Malinauskas, A Electrochimica Acta 2006, 51, 6025-6037.
2
  Janata. J; Josowics, M Nature Materials 2003, 2, 19-24.
3
  Gangopadhyay, R; De, A Chem. Mater. 2000, 12, 608-622.
4
  Maliakai, A; Katz, H; Cotts, P.M; Subramoney, S; Mirau, P J.A.C.S 2005, 127, 14655-14662.
5
  Zhang, Q. M; Li, H; Poh, M; Xia, F; Cheng, Z-Y; Xu, H; Huang, C Nature 2002, 419, 284-287.
6
  Lu, J; Moon, K-Y; Kim B-K; Wong, C.P Polymer 2007, 48, 1510-1516.
7
  Jang, J; Yoon, H Small 2005, 1, 1195-1199.

				
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