Carbon Nanotubes / polymer nanocomposites
The objectives of our research on Carbon Nanotubes / polymer nanocomposites are :
- To use Carbon Nanotubes (CNT) at the macroscopic scale by embedding them into a polymer matrix
- To transfer the physical properties of the nanotubes to a polymer matrix by controlling the CNT/polymer interaction
- Basic studies
- Possible applications as transparent electrodes, injection polymer layers…
CNT/PMMA Nanocomposites :
The PhD thesis of C. Stéphan (2000), J.M. Benoit (2001) and P. Bonnet (2005) were at the origin of our investigations on this kind of nanocomposites. Single walled nanotubes (SWNT) / polymethylmetacrylate (PMMA) nanocomposites may benefit from the electrical conductivity of the CNT and from the optical transparency of PMMA. It is of interest for applications as transparent electrodes, injection layers or antistatic layers…
We have shown that the electrical properties of the composite are due to the percolation of the SWNT network. The charge transport occurs through hopping. The Coulomb mesoscopic charge effect influences the low temperature conduction properties. Magnetotransport and non linear conduction properties suggest that the charge transport is balistic at the nanotube scale.
The thermal conductivity of the nanocomposites has been studied in collaboration with B. Garnier from Lab Thermocinetique .The thermal conductivity of the polymer is enhanced by 50% when adding 8% of CNT. Despite its small magnitude, this effect is due to the percolation of the SWNT.
|Figure 1: SWNT/PMMA micrograph||Figure 2: Room temperature electrical
conductivity of SWNT/PMMA composites
versus the SWNT amount.
|Figure 3: Low temperature non linear
electrical conductivity of a 0.4%
SWNT/PMMA composite film. .
CNT/Polyaniline Nanocomposites :
SWNT or Multiwalled nanotubes (MWNT) / Polyaniline nanocomposites were prepared in collaboration with W. Maser (CSIC Zaragossa) or M. Baibarac and I. Baltog (NIMP, Bucharest) by in situ or ex situ polymerisation in different conditions. They have been studied by Raman scattering spectroscopy, atomic force or transmission electron microscopies or by measuring their transport properties. We are interest in the specific interaction between the polymer and the CNT due to the conjugated nature of polyaniline.
Depending on the preparation route, charge transfer, covalent interaction of simple physisorption have been observed. Raman spectroscopy is a very useful tool in these studies since it allows to survey what is going on both from the polymer of from the CNT point of view.
The electrical properties of the composites can be described as arising from two parallel conduction path ways or from a doping of the polyaniline according to the CNT/polymer interaction. There is no evidence of electrical percolation in this kind of composite.
|Figure 4: Low temperature magnetoresistance
of a 8% SWNT/PMMA composite film.
|Figure 5: Room temperature thermal conductivity of
SWNT/PMMA composite films versus the SWNT amount.
Inset : contribution of the SWNT network.
SWNT / PPV Nanocomposites :
Polyparaphenylene vinylene (PPV) and derivatives are photoluminescent conjugated polymers which are widely studied and used for optoelectronic (OLED) applications. Our works in this field focus mainly on the relationship between the structure and the electronic properties of the polymer that we probe through the vibrations or the excitons dynamics.
SWNT/PPV composite thin films have been prepared by mixing CNT (from 0 to 64 wt % ) and a precursor of PPV. The dispersion is deposited on silica or on a silicium subtsrate and heated at 300°C in order to polymerise the PPV.
Optical absorption and photoluminescence of the films show that the polymerisation is delayed when the SWNT amount x increases. It results in shorter conjugation length chains in the composites than in pure PPV.
The presence of shorter conjugation length is also evidenced from Raman scattering and IR absorption spectroscopies. Raman spectroscopy suggests also that the SWNT bundles are bigger in the composites than in pure SWNT samples.
The SWNT/PPV composite films exhibit a photoconductivity response. The photocurrent is increasing with the SWNT content following a percolation behaviour with a 2 wt % threshold. The excitons may diffuse along the SWNT percolation network. It inhibits the radiative decay of the excitons which in turn enhances the photocurrent. The presence of nanotubes in the polymer has thus two main effects: a shortening of the conjugation length and a quenching of the luminescence.
In collaboration with E. Mulazzi (Milano), we have developed a model of the polymer in the composites which allows to describe the optical absorption, the Raman and the photoluminescence spectra. This model assumes that the PPV chains can be divided in two families (a bimodal distribution is used): oligomers with short conjugation length and oligomers with long conjugation length. This model gives a very good quantitative and qualitative agreement with the lineshapes that are observed in optical spectroscopies and with their evolution. It shows that the excitons are blocked on the short chains because of the chain defects and thus the energy is not easily transferred from a short to a long chain. We propose thus a new interpretation of the photoluminescence spectra. The two main peaks are attributed to distinct transitions arising from short or long chains. The increase of the intensity of the peak at high energy is associated to an increase of the disorder.
This model suggests that the PPV or SWNT/PPV composites films have an heterogeneous morphology with two different regions: (i) amorphous regions with short (conjugation length) chains where the excitons are not free to move (ii) quasi-cristalline regions with long (conjugation length) chains where the excitons can migrate and dissociate. Complementary X ray diffraction and optical absorption studies support our model. Time resolved photoluminescence studies are on going from which we expect additional informations.Beyond the basic studies, our work shows that adding SWNT to PPV may be a way to control the blue emission of the polymer.
Au delà de l'aspect fondamental, ces différentes études montrent que les composites PPV/NTC ont des propriétés optoélectriques intéressantes et il est possible de contrôler l'émission dans le bleu des échantillons par un choix correct du pourcentage des NTC dans les films.
Figure 8: Room temperature normalized photoluminescence ( E exc= 2.8 eV.) spectra of a pure PPV film with different dilution rates of the precursor: (a) dilution 1/4; (b) dilution 1/10 et (c) dilution 1/20.
Team of research
person in charge : Olivier Chauvet (PR), Jany Wery (DR)
- Jean-Pierre. Buisson (CR)
- Eric Faulques (CR)
- Christine Godon (MC)
- Serge Lefrant (PR)
- Jean-Yves Mevellec (IR)
Student : Florian Massuyeau (Th)
Collaborations : M. Baibarac, I. Baltog, L. Mihut, E. Mulazzi, W. Maser, B. Garnier, V. Ivanov
Contrats, programmes : PAI Brancusi (2005-2006)
- Thermal properties and percolation in carbon nanotubes polymer composites
P. Bonnet, D. Sireude, B. Garnier, O. Chauvet
Applied Physics Letters, 91, 201910 ( 2007)
also in Virtual Journal f Nanoscale Science & Technology, 26 Nov 2007
- Evidence of charge migration on conjugated segments from Photoluminescence spectra of:poly(paraphenylene vinylene) and poly(paraphenylene vinylene) single-walled carbon nanotubes composite films
F. Massuyeau, ,H. Aarab, L. Mihut, S. Lefrant and E. Faulques E. Mulazzi, R. Perego and Wéry J
J. Chem. Phys., 125(1), 014703 (2006)
- A soluble and highly functionnal polyaniline-carbon nanotube composite
R. Sainz, AM. Benito, MT Martinez, J.F. Galindo, J. Sotres, AM. Baro, B. Corraze, O. Chauvet, AB. Dalton, RH Baughman; WK. Maser
Nanotechnology 16, S150 (2005) http://www.iop.org/EJ/abstract/0957-4484/16/5/003
- Soluble self aligned carbon- nanotube/ polyaniline composites
R. Sainz, AM. Benito, MT Martinez, J.F. Galindo, J. Sotres, AM. Baro, B. Corraze, O. Chauvet, WK. Maser
Advanced Materials 17, 278 (2005) http://www3.interscience.wiley.com/cgi-bin/abstract/109895960/ABSTRACT
- Electrical and optical properties of poly(paraphenylene vinylene) and single-walled carbon nanotubes composite films
H. Aarab, M. Baïtoul, J. Wéry, S. Lefrant, E. Faulques, J.L. Duvail and M. Hamedoun
Synth. Met., 115, 63-67, (2005).
- Optical properties of carbon nanotubes-PPV composites: influence of the PPV conversion temperature and nanotubes concentration
Mulazzi E, Perego R, Aarab H, L. Mihut, S. Lefrant, E. Faulques and J. Wéry
Synth. Met., 154 (1-3): 221-224 Sp. Iss. (2005)
- Photoconductivity and optical properties in composites of polyparaphenylene vinylene and single called carbon nanotubes
E. Mulazzi, R. Perego, H. Aarab, S. Lefrant, E. Faulques, J. Wery
Phys. Rev B 70, 155206 (2004) http://link.aps.org/abstract/PRB/v70/e155206
- Covalent functionnalization of single-walled carbon nanotubes with polyaniline evidenced by Raman and FTIR spectroscopy
M. Baibarac, I. Baltog, C. Godon, S. Lefrant, O. Chauvet
Carbon 42, 3143(2004) http://dx.doi.org/10.1016/j.carbon.2004.07.030
- Electrical, magneto-transport and localization of charge carriers in nanocomposites based on carbon nanotubes
O. Chauvet, J.M.Benoit, B. Corraze
Carbon, 42, 949 (2004) http://dx.doi.org/10.1016/j.carbon.2003.12.020
- Photoexcitations in composites of polyparaphenylene vinylene and single walled carbon nanotubes
J. Wery H. Aarab, S. Lefrant, E. Faulques, E. Mulazzi, R. Perego
Phys. Rev. B 67, 115202 (2003) http://link.aps.org/abstract/PRB/v67/e115202
- Polyaniline and carbon nanotubes based composites containing units and fragments of nanotubes
M. Baibarac, I. Baltog, S. Lefrant, J.Y. Mevellec, O. Chauvet
Chem. Mat, 15, 4149(2003) http://dx.doi.org/10.1021/cm021287x
- "Localization, Coulomb interactions and electrical heating in single-wall carbon nanotubes/polymer composites"
J.M. Benoit, B. Corraze, O. Chauvet
Phys. Rev. B, 65 241405(R) (2002) http://link.aps.org/abstract/PRB/v65/e241405
- "Raman spectroscopy and conductivity measurements in polymer-multiwalled carbon nanotubes composites"
C. Stéphan, T.P.Nguyen, B. Lahr, W. Blau, S. Lefrant, O. Chauvet
J. Mater. Res, 17. 396 (2002)
- « Synthesis of a new polyaniline/nanotube composite : in situ polymerisation and charge transfer through site-selective interaction »
M. Cochet, W.K. Maser, A.M. Benito, M. A. Callejas, M. T. Martinez, J.M. Benoit, J. Schreiber, O. Chauvet
Chem. Com. (16) 1450 (2001) http://www.rsc.org/Publishing/Journals/CC/article.asp?doi=b104009j